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danjones
super member


Reged: 09/26/12

melting pyrex for blanks
      #5583465 - 12/22/12 12:48 AM Attachment (101 downloads)

I'm using a high fire ceramic kiln for making blanks. the set up is not finished, as I am making a ramp/soak controller to control the temp thru the stages of melting the glass and the annealing process, which is all worked out and in testing, but looking successful. In a trial run with plate glass, what i'm primarily using, the blank was not bad for a first attempt. useable as a tool. my question is about pyrex. I understand that pyrex cookware today is not exactly true pyrex, but does contain boron, which plays a big role in the thermal expansion, which is why it's used for baking. what about melting it down into a mirror blank. i can do up to 17" in my kiln and thick as i want. i see a ton of good clear "pyrex" cookware at garage sales all the time.

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alancygnusx2
professor emeritus


Reged: 11/25/08

Loc: CA
Re: melting pyrex for blanks new [Re: danjones]
      #5583471 - 12/22/12 12:54 AM

Very cool Dan, how hot does the kiln need to get for the melting?

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danjones
super member


Reged: 09/26/12

Re: melting pyrex for blanks new [Re: alancygnusx2]
      #5583503 - 12/22/12 01:43 AM

the kiln will reach just over the 2300 degree mark. plate plass will melt at just under 1800. so called pyrex will melt at just a bit higher, but well within what the kiln will do. the glass needs to heat thru certain stages, soaking along the way, then reheated for the annealing process. thats where the controller comes into play, to control all this. (thank goodness for ebay). my first test wasnt really to make a blank, but more for testing the heat capacity of the kiln, which is awesome. i thought since i'm going to fire it high, why not throw in a mold and some glass and see what happens. i for sure got a blank, little rough around the edges, and not annealed at all. just a test piece or use for a tool. controller will do it. i just read that the company that bought 'pyrex' hasn't changed its formula in like 45 years. it's a type of soda lime glass chemically enhanced to have the same properties of the very old borosilicate glass. the pyrex brand is everywhere. wondering if this stuff will work having a better thermal quality than ordinary plate.

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Mark Harry
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Re: melting pyrex for blanks new [Re: danjones]
      #5583670 - 12/22/12 08:00 AM

Just read about the soda-lime glass pyrex 'replacement'. and there have been quite a few more episodes of exploding bakeware. It shows that the expansion characteristics aren't as good as the old borosilicate stuff.
My 2 cents, the replacement may not quite be as easy to melt or slump into a blank??? You'll have to tell us how it works out.
I remember one of the names making that 'blue' pyrex is Anchor-Hocking or similar, but can't recall what the other was that is a major supplier.
M.


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Achernar
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Reged: 02/25/06

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Re: melting pyrex for blanks new [Re: danjones]
      #5583873 - 12/22/12 11:06 AM

Laboratory glassware is also made of Pyrex, if you can find some it would be borosilicate glass that would make an excellent mirror blank.

Taras


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kfrederick
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Reged: 02/01/08

Re: melting pyrex for blanks new [Re: Mark Harry]
      #5583874 - 12/22/12 11:06 AM

http://www.mdpub.com/scopeworks/index.html might be some use full info

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DAVIDG
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Reged: 12/02/04

Loc: Hockessin, De
Re: melting pyrex for blanks new [Re: kfrederick]
      #5584133 - 12/22/12 01:46 PM

Most modern "Pyrex" is not borosilicate glass at all. What is done is the glass is thermally stressed on the outer skin in the manufacturing processes to make it shatter resistance from thermal shock. This is why you hear of exploding cookware when it fails. The trade name of "Pyrex" has been licensed by Corning and no longer means one is buying borosilicate glass of the same chemical make up as true Pyrex.

- Dave


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KenScharf
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Reged: 12/16/12

Loc: South Fla
Re: melting pyrex for blanks new [Re: DAVIDG]
      #5584158 - 12/22/12 02:01 PM

In the sizes that you are thinking there is nothing really wrong with common "Plate" glass for mirrors. The 60" and 100" telescopes on Mt Wilson worked very well for years, they are both thick plate glass. True, those scopes do take time to adjust to a rapid change in temperature so sometimes they couldn't be put into service for several hours after sundown. But those mirrors are MUCH larger and THICKER than what are used in today's Dob's. The worst thing about plate glass is that you might need to wait several hours after a figuring session before you can get a good test "reading".

I saw Mike's web pages and want to look for a Kiln and try his method some day. BTW a while back I found some large candle holder glass at Bed Bath and Beyond. These are a bit larger than 8" in dia. and 3/4" thick in the middle, with a 1/2" high wall around the sides to hold the (large!) candle. I wondered if two of these could be melted to make a 9-10" mirror blank.


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seryddwr
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Reged: 02/19/10

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Re: melting pyrex for blanks new [Re: KenScharf]
      #5584177 - 12/22/12 02:16 PM

Do they make kilns large enough for a 30" blank? Preferably old and cheap ones? The controller would need to cool the kiln for much longer, but...

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KenScharf
member


Reged: 12/16/12

Loc: South Fla
Re: melting pyrex for blanks new [Re: seryddwr]
      #5584203 - 12/22/12 02:34 PM

Probably. Someone near me has a kiln for sale that has a chamber 2'wide by 40" tall. I've seen Kilns that are made for firing plates that are very wide but not very tall. That's what you'd want. I'll probably pass on the kiln since it's too big for what I want, and I'd have to re-wire the garage outlet from 20A to 30A to handle it. BTW, it's on Craig's list in Hollywood Fla if anyone is interested.

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seryddwr
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Reged: 02/19/10

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Re: melting pyrex for blanks new [Re: KenScharf]
      #5584313 - 12/22/12 04:03 PM

Well, it's a ways down on my list, but I've got the structure for a 30" telescope. That I wasn't able to get optics for. (I was cheated out of said optics.)

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Norm Meyer
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Reged: 02/08/09

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Re: melting pyrex for blanks new [Re: KenScharf]
      #5584342 - 12/22/12 04:36 PM

This topic is very interesting I'd like to try it some day.
One thing to consider is the economic feasibility. Would it
cost me more to make my own than it would be to buy one.Other
than the fun factor which you can't put a price on. Maybe as a
group project where you could make more than you could use yourself thus lowering the per unit cost. I like the possibility of making cellular mirrors making them lighter.
good plate glass is fairly plentiful at reasonable cost.
The price of the kiln wouldn't be as big a factor as the cost of the electricity to run it.
The 100" mirror was basically green wine bottles cause that's what St Gobain was making. They had to pour in
several batches cause they didn't have the capacity to melt
it all at once. It is full of bubbles and what looks like waves. In fact Ritchey wanted to refuse the blank but his
superior said no. In fact I don't think he showed up for first light because he was sure it wouldn't work, but it did
and very well at that.
That was probably more than 2 cents worth.
Norm


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KenScharf
member


Reged: 12/16/12

Loc: South Fla
Re: melting pyrex for blanks new [Re: Norm Meyer]
      #5584387 - 12/22/12 05:27 PM

I've read an estimate of the cost of fusing a mirror blank of about 10-12" at about $25 for the cost of the electric power. That will vary depending on what you pay for a KWH. The cost of the kiln? Well you can find used ones for about $100-500, new they are around $1000 but that depends on size. Most kilns don't have a suitable temperature controller for the slow ramp up/down needed for glass though you can babysit the thing and run it by hand if you have a good pyrometer in the thing. An automated temperature controller would add a few hundred to the cost. BUT the hw costs would be figured over making more than one mirror, otherwise the cost of buying a blank would be cheaper than making your own. If I were in the business of making telescope mirrors It's something I'd consider having in the shop (as well as an Aluminumizing chamber). I'm currently in the process of trying to make my own 7" mirror from thin plate glass. If the project comes out usable I would want to try making a slightly larger second mirror. The hobby could lend itself toward a nice retirement business for someone, who knows?

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orlyandico
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Re: melting pyrex for blanks new [Re: KenScharf]
      #5584743 - 12/22/12 09:31 PM

I saw this one and it's very interesting...

http://www.instructables.com/id/Casting-a-Large-Light-Weight-Telescope-Mirror...

Basically a cellular mirror (and not the glued-on-posts thing that Hubble Optics makes).

The labor of making all the little hexes must be substantial, but there's an almost 50% weight savings. Might be a business model there... since I don't know of anyone selling cellular blanks.


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danjones
super member


Reged: 09/26/12

Re: melting pyrex for blanks new [Re: orlyandico]
      #5584955 - 12/23/12 12:40 AM

thanks for all the comments. mike is exactly where i got the idea at mdpub.com. i even trepanned glass at 1" to start with, but it's so hard to come by. i have the kiln, got it cheap from an art studio, and can do up to 17" in it, needing an inch for the mold. trial was okay, but really just testing the kiln out. there's a ton of plate glass around here of all thicknesses, so easy to come by. as far as the cost of the kiln to run, shouldn't be too bad here. using the ramp/soak controller im building now to control the temp, ebay is keeping the cost to just a few dollars actually. the controller is in process now. the world kitchen site that bought out corning states it hasnt changed the formula in 45 years, so this is where the controversy begins. if one was buying pyrex 20 or so years ago, then it should be the same formula according to world kitchen. this is my question. i have no problem using plate, just was wondering about the pyrex if i could get better quality. i'm actually putting together a site for fun about the whole experience, from trepanning, to the kiln blanks, grinding, the aluminizing. I got my diffusion pump this week and also working on the vac chamber, which will have to be another thread, also viewable on my site. thanks for the feedback and let's come to a conclusion on the modern pyrex. Read it from the world kitchen site, quality or not?

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glennnnnnn
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Reged: 10/20/09

Loc: San Diego, CA
Re: melting pyrex for blanks new [Re: danjones]
      #5584987 - 12/23/12 01:11 AM

You'd probably have better luck making your own glass from scratch rather than trying to melt and recycle glass that may or may not be the exact, same formula. If it is, good. If it isn't, you produce an expensive paperweight that warps and bends with temperature variations.
The glass should be of a uniform type throughout the structure of the blank. The only way to guarantee this is to make the glass, which you won't be able to do with your kiln. You need large crucibles and furnaces for much higher temperatures. You have to melt and stir the mix(es) in the right proportions, and even though you might know the ingredients there might well be proprietary steps that are still trade secrets. This would be something that has "Caution, May Cause Death" written all over it.


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seryddwr
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Re: melting pyrex for blanks new [Re: glennnnnnn]
      #5585032 - 12/23/12 02:11 AM

That's why the guy on instructables recommended using a single tabletop for a single blank (At least on the hex blank), to try to achieve uniformity. The U of A mirror lab buys chunks of borosilicate glass, from O'Hara.

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Jon Isaacs
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Re: melting pyrex for blanks new [Re: glennnnnnn]
      #5585071 - 12/23/12 03:52 AM

Quote:

You'd probably have better luck making your own glass from scratch rather than trying to melt and recycle glass that may or may not be the exact, same formula. If it is, good. If it isn't, you produce an expensive paperweight that warps and bends with temperature variations.
The glass should be of a uniform type throughout the structure of the blank. The only way to guarantee this is to make the glass, which you won't be able to do with your kiln. You need large crucibles and furnaces for much higher temperatures. You have to melt and stir the mix(es) in the right proportions, and even though you might know the ingredients there might well be proprietary steps that are still trade secrets. This would be something that has "Caution, May Cause Death" written all over it.




The homogeneity/uniformity of glass made by remelting glass was what immediately came to my mind. In the remelting process, the glass is probably not well enough mixed that it is satisfactorily homogenized. If the glass is not uniform through out, then there will be small but meaningful variations in the coefficient of thermal expansion which result in unavoidable thermal stresses if the temperature changes. Annealing eliminates the thermal stresses in a uniform material but cannot address those in a inhomogeneous material.

If a batch consisted of 10 pieces of real pyrex and just one piece of fake pyrex, there would be serious variations in the composition throughout the mirror with resulting differences in the CTE, the differences in the CTEs of the two materials differ by a factor of about 2.5x. That would result in large thermal stresses. But I suspect even different between different glass within a type are sufficient to cause problems.

Given that real pyrex seems have been off the market for a good long time, it seems the best bet is to just make the mirror with some well annealed plate glass.

Jon


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Mirzam
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Re: melting pyrex for blanks new [Re: Jon Isaacs]
      #5585151 - 12/23/12 06:58 AM

Might be interesting to try and make some slumped meniscus mirror blanks, either from thin pyrex blanks or from plate glass.

JimC


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Pinbout
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Re: melting pyrex for blanks new [Re: Mirzam]
      #5585227 - 12/23/12 08:48 AM

Quote:

make some slumped meniscus mirror blanks, either from thin pyrex blanks




or take a 10"x1-3/4" and make a thin 12"


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glennnnnnn
sage


Reged: 10/20/09

Loc: San Diego, CA
Re: melting pyrex for blanks new [Re: Pinbout]
      #5585428 - 12/23/12 11:34 AM

I think that's a very good idea! Slumping plate glass is not a difficult project, and the generated curve would be a huge time-saver.
There's something about Pyrex that I don't quite understand: how could a product with such usefulness and value just be pulled out of production?
I think that the answer is more complicated than just business buying and selling, and may involve the EPA and other agencies.


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DAVIDG
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Re: melting pyrex for blanks new [Re: glennnnnnn]
      #5585463 - 12/23/12 11:56 AM

Quote:

I think that's a very good idea! Slumping plate glass is not a difficult project, and the generated curve would be a huge time-saver.





A group of 6 of us are doing exactly that with 16" x 3/4" blanks to make 16" f/3 newtonians. We will be grinding and polishing them at the next Delmarva Mirror Making class http://www.delmarvastargazers.org/archive/mw13/MMM13.html after they have been slumped in one of our members kiln.

- Dave


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ccaissie
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Reged: 09/13/10

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Re: melting pyrex for blanks new [Re: KenScharf]
      #5585466 - 12/23/12 11:58 AM

Quote:

BTW a while back I found some large candle holder glass at Bed Bath and Beyond. These are a bit larger than 8" in dia. and 3/4" thick in the middle, with a 1/2" high wall around the sides to hold the (large!) candle. I wondered if two of these could be melted to make a 9-10" mirror blank.




Or maybe they could be re-annealed to higher usable specs?


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KenScharf
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Reged: 12/16/12

Loc: South Fla
Re: melting pyrex for blanks new [Re: ccaissie]
      #5585773 - 12/23/12 03:04 PM

Quote:

Quote:

BTW a while back I found some large candle holder glass at Bed Bath and Beyond. These are a bit larger than 8" in dia. and 3/4" thick in the middle, with a 1/2" high wall around the sides to hold the (large!) candle. I wondered if two of these could be melted to make a 9-10" mirror blank.



Or maybe they could be re-annealed to higher usable specs?



The problem is that as these disks are right now they are useless for a mirror blank. One surface is a dish with a 1/2 inch wide, 1/2" high dam around the edge. The bottom is not flat with lots of concentric ridges in it. Remelting the glass into a flat disk would be better than trying to grind both sides flat (and wasting a lot of glass). It would also result in a thicker disk. If remelting is possible, I could make a 9-10" blank out of the two 8" candle holders. I don't see problems in melting pieces of glass to make a larger item if all the glass came from the same source (IE: a single large sheet or several sheets of the same type. Those candle holders are identical). As far as Pyrex goes, well the market is flooded with cheap *BLEEP* from China. That's where the problem glass comes from.

Edited by KenScharf (12/23/12 03:05 PM)


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Mirzam
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Re: melting pyrex for blanks new [Re: DAVIDG]
      #5585942 - 12/23/12 04:59 PM

Got any more blanks?

JimC


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danjones
super member


Reged: 09/26/12

Re: melting pyrex for blanks new [Re: Mirzam]
      #5586278 - 12/23/12 09:15 PM

Melting glass into blanks in a high fire kiln....I'm not reinventing the wheel here. I'm following in the foot steps of someone who is already currently successful at it. The steps can be seen at mdpub.com if interested. I'll be using peices of glass all from the same piece or item, like all from a big tabletop for example for one blank. The glass in one blank will be made with only glass thats from the tabletop, to prevent incompatibilities. This is already being successfully done. From what i've read on world kitchens site, the pyrex formula has not changed in 45 years. Interesting.

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davidpitre
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Re: melting pyrex for blanks new [Re: orlyandico]
      #5586321 - 12/23/12 09:48 PM

Quote:

Might be a business model there... since I don't know of anyone selling cellular blanks.




http://www.dreamcellularllc.com/40cm.htm


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danjones
super member


Reged: 09/26/12

Re: melting pyrex for blanks new [Re: Mirzam]
      #5586420 - 12/23/12 11:00 PM

i do have a couple of 6" x 1" tinted blanks mirzam. were you the one who emailed me about them?, if so, i emailed you back but then never heard again. I'm grinding a 10" now made from the same chunk of plate, so far so good. No issues about the glass. thanks.

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danjones
super member


Reged: 09/26/12

Re: melting pyrex for blanks new [Re: danjones]
      #5586435 - 12/23/12 11:16 PM

http://pyrexware.com/index.asp?pageId=30#TruthID6
This is the link where they talk about the coposition of pyrex cookware. and interesting read. Pyrex states here that they haven't used true borosilicate glass since the 1940's. They also imply that the current mix has similar properties to the original pyrex. I think of 2 questions after reading this: if the properties are so close, why couldn't a guy melt down a stack of clear 'pyrex' pie dishes in a kiln, anneal it thru a proven,successful firing stage and get a decent blank? (strain test included of course). And if true borosilicate glass hasn't been around for so long, and hard to find chunks of this glass, then where are the people who are selling 'pyrex' blanks getting the glass to make them? Interesting. Controversy is fun.


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danjones
super member


Reged: 09/26/12

Re: melting pyrex for blanks new [Re: danjones]
      #5586458 - 12/23/12 11:34 PM

Just being clear also, I'm not just guessing about how to fire the plate glass. I tested the kiln once, just really to test the heating capacity of the kiln, and went ahead and melted some plate in a mold i made and melted it down. I didn't anneal it all, that wasnt my test. now satisfied the heat is good, i'm building a controller to control the ramp/soak/cooling cycle of the kiln to a specific firing schedule created just for this purpose. I'm following already successful steps, not trying it out. Good stuff.

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Dave O
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Re: melting pyrex for blanks new [Re: danjones]
      #5586610 - 12/24/12 02:48 AM

Quote:

From what i've read on world kitchens site, the pyrex formula has not changed in 45 years. Interesting.




It is my understanding that the 'problem' is that not all glassware labeled "Pyrex" is MADE from that glass.


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Mirzam
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Re: melting pyrex for blanks new [Re: danjones]
      #5586651 - 12/24/12 04:52 AM

Hi Dan,
No, it was not I that emailed you about the 6" blanks. I was asking DaveG about the slumped 16" blanks that are being prepared for the next Delmarva workshop. Sorry to go OT.

JimC


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Mark Harry
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Re: melting pyrex for blanks new [Re: Dave O]
      #5586697 - 12/24/12 06:47 AM

Precisely
M.


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danjones
super member


Reged: 09/26/12

Re: melting pyrex for blanks new [Re: Mark Harry]
      #5587920 - 12/25/12 12:20 AM

I've been noticing all the wife's glass bakeware. On all of ours, it has brand 'pyrex' embedded into the glass along with the copywrite insignia. To me, this would mean it would have to be made from the copywrite owner, which would be world kitchen. They claim the formula for pyrex hasn't changed since the 1940's. If so, shouldn't the composition be just the same as it was all these years? I'm thinking that simply because it's not borosilicate, it wouldn't work for a blank. Pyrex hasn't been borosilicate since the late 30's. Thanks for all the feedback.

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glennnnnnn
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Reged: 10/20/09

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Re: melting pyrex for blanks new [Re: danjones]
      #5587949 - 12/25/12 12:55 AM

I had always assumed that Pyrex was borosilicate glass, and there was never any mention of the soda lime composition. There's got to be a reliable test to tell one from the other. Refractive Index? Abs/trans spectrum?

OF COURSE, Density! Thanks Jon!

Edited by glennnnnnn (12/25/12 11:11 AM)


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Jon Isaacs
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Re: melting pyrex for blanks new [Re: glennnnnnn]
      #5588149 - 12/25/12 07:08 AM

Quote:

I had always assumed that Pyrex was borosilicate glass, and there was never any mention of the soda lime composition. There's got to be a reliable test to tell one from the other. Refractive Index? Abs/trans spectrum?




The density of 7740 Pyrex is about 2.23 grams/cc where as the density of soda-lime about 2.44gm/cc. If one has a reasonably accurate scale one can use the Archimedes principle to determine the density with sufficient accuracy. In the lab at work, I have a digital scale with a capacity of 15Kg that measures to 0.1 gram, I have used this with mirrors up to 16 inches to measure the density of the glass.

Still, I think the homogeneity of the glass could still be a problem even if the glass is all Pyrex, it really should come from the same batch.

Jon


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KenScharf
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Reged: 12/16/12

Loc: South Fla
Re: melting pyrex for blanks new [Re: Jon Isaacs]
      #5588267 - 12/25/12 10:03 AM

Small diameter pyrex mirror blanks are still not that rare or expensive today. I've seen several for sale here on the classified page. It might be possible to melt several 6" or smaller blanks to make a larger and thicker one.

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Pinbout
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Re: melting pyrex for blanks new [Re: KenScharf]
      #5588271 - 12/25/12 10:08 AM

firsthand discovery sells supremax33 6in for $50 and 8in for $100.

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JohnH
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Re: melting pyrex for blanks new [Re: Pinbout]
      #5588345 - 12/25/12 11:22 AM

What about melting a 16" 3.25" inch thick one into a thinner one?

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TxStars
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Re: melting pyrex for blanks new [Re: Jon Isaacs]
      #5589171 - 12/26/12 02:20 AM

Isn't the old way of mixing glass to cast/break/re-cast several times?

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Pinbout
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Re: melting pyrex for blanks new [Re: JohnH]
      #5589318 - 12/26/12 08:46 AM

A 16 x 3.25 would make a 24 x 1.5?

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careysub
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Re: melting pyrex for blanks new [Re: danjones]
      #5589562 - 12/26/12 11:41 AM

You can buy authentic Corning Pyrex 1" rod for $8 a pound (a 4 foot 1" rod weighs 3 lb) from glass blowing supply places:

http://www.waleapparatus.com/catalog.asp?prodid=547940&showprevnext=1

It appears the Pyrex brand name was sold to World Kitchen just for the cookware product line.

http://www.corning.com/lifesciences/us_canada/en/technical_resources/product_...


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careysub
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Re: melting pyrex for blanks new [Re: danjones]
      #5589578 - 12/26/12 11:52 AM

Quote:

http://pyrexware.com/index.asp?pageId=30#TruthID6
This is the link where they talk about the coposition of pyrex cookware. and interesting read. Pyrex states here that they haven't used true borosilicate glass since the 1940's. They also imply that the current mix has similar properties to the original pyrex. I think of 2 questions after reading this: if the properties are so close, why couldn't a guy melt down a stack of clear 'pyrex' pie dishes in a kiln, anneal it thru a proven,successful firing stage and get a decent blank? (strain test included of course). And if true borosilicate glass hasn't been around for so long, and hard to find chunks of this glass, then where are the people who are selling 'pyrex' blanks getting the glass to make them? Interesting. Controversy is fun.




There is no company called Pyrex.

It is brand-name still used by Corning for its borosilicate scientific glass and glassware which it still makes:
http://www.corning.com/lifesciences/us_canada/en/technical_resources/product_...

Corning sold its use of Pyrex for cookware to World Kitchen in 1998 when it dropped its consumer cookware business. The pyrexware.com website is a World Kitchen website.

World Kitchen claims its tempered soda lime glass is functionally equivalent to borosilicate glass, not that it has the same composition.

I would not take World Kitchen's claim that Corning was making tempered soda lime glass for decades under the brand-name Pyrex as fact without independent confirmation of some sort, like a statement from Corning, or someone actually measuring the density of an old piece of cookware.

You can buy borosilicate glassware under the name Marinex produced in Brazil.


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careysub
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Re: melting pyrex for blanks new [Re: glennnnnnn]
      #5589587 - 12/26/12 11:57 AM

Quote:

... There's something about Pyrex that I don't quite understand: how could a product with such usefulness and value just be pulled out of production?




You never saw a product with an established brand-name be replaced with a cheaper substitute trading on the original's reputation?

This is extremely common, I would say the rule rather than the exception, when a brand-name is sold to another company that did not build up the brand's rep. This is what happened here when Corning sold off its consumer product line to World Kitchen.

Quote:

I think that the answer is more complicated than just business buying and selling, and may involve the EPA and other agencies.




Why would you think this?

Maximizing profit is more than sufficient explanation.

NB: Just within the realm of cookware I can cite several examples of former prestigious brands being debased with cheaper knock-offs.

World Kitchen not only did this (apparently) with Pyrex cookware, they also did it with Magnalite - a premium brand of cast magnesium cookware (hence its name) dating from 1934 now consisting only of cheaper and heavier cast aluminum.

Revere Ware once consisted of premium stainless steel pots clad to a disk of copper for rapid heat distribution. The pots today have the same appearance, but the "copper bottom" is now thin plating for show, which quickly wears off in an unsightly manner.

West Bend was once a brand of cookware that produced a very popular and nifty electric wok (famous for its red enamel exterior) with a thermostatic control. I used mine for decades until it finally wore out, and bought a new "West Bend" wok, to find that the "control" was now just a potentiometer and the "temperature" scale on it meant nothing. After burning the first dinner I tried to cook in it, and then have it shed screws and nuts into my garbage disposal, destroying it, I threw the worthless thing out.

Regal has been cheapening its own classic line of cast aluminum cookware, with ever thinner and more poorly cast products.

This is a very, very common practice. U.S. made real premium cookware is mostly a thing of the past it seems.

Edited by careysub (12/26/12 02:00 PM)


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glennnnnnn
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Re: melting pyrex for blanks new [Re: careysub]
      #5590274 - 12/26/12 08:40 PM

Oh. Corporate raiders of the worst kind.
I remember about 10 years ago when there was some rumbling about the impending Corning break-up and how Pyrex might become a thing of the past. But there was also mention of the process being too expensive and also environmentally less than friendly. The interpretation from this was that Corning divested itself of the product rather than upgrade and retool for the environmental issues.
As for the other examples, I agree. It seems the quality in mass-produced articles has gone. Exported to cheaper labor markets. What we can buy then is no bargain.
I have a bunch of excellent old Revere pots- the closest you can get quality-wise to those is pots imported from Europe that cost more than a hundred dollars each.
The moral of this is that the world changes and we need to change with it... But there's always the possibility that someone will come up with something better!


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careysub
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Re: melting pyrex for blanks new [Re: glennnnnnn]
      #5590403 - 12/26/12 10:17 PM

Quote:

...The interpretation from this was that Corning divested itself of the product rather than upgrade and retool for the environmental issues....




I have seen this same story (in my efforts to find replacements for my very faded and increasingly chipped Pyrex measuring pitchers). But I will note that it conflicts with World Kitchen's claim that Corning was making tempered soda-lime cookware for decades anyway, and one does wonder what sort of environmental issue would affect borosilicate and not soda lime manufacture. Corning still makes Pyrex for other markets.

Scapegoating other parties to excuse their business decisions is hardly an unheard of corporate practice.


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careysub
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Re: melting pyrex for blanks new [Re: Jon Isaacs]
      #5590411 - 12/26/12 10:22 PM

Quote:


The density of 7740 Pyrex is about 2.23 grams/cc where as the density of soda-lime about 2.44gm/cc. If one has a reasonably accurate scale one can use the Archimedes principle to determine the density with sufficient accuracy. In the lab at work, I have a digital scale with a capacity of 15Kg that measures to 0.1 gram, I have used this with mirrors up to 16 inches to measure the density of the glass.

Jon




I took a crack at this with my old, old Pyrex measuring pitchers (I have gram-accurate digital scales), but found that my attempts to measure displacement with kitchen equipment were less precise than required to distinguish the densities (I tried both measuring volume change, and the mass of overflow).

I have a digital luggage scale (suspension hook type) that I will break out to see if I can distinguish the weight change from immersion without trying to measure displacement. It may not be accurate enough though.


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glennnnnnn
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Re: melting pyrex for blanks new [Re: careysub]
      #5590964 - 12/27/12 10:45 AM

You would need to be very accurate just to get a "yes or no."
A more reliable method would be spectrographic analysis of the visible or UV absorption bands. There would be some characteristic of each glass type that would be easily identified if you happened to have a spectroscope.


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rcdk
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Re: melting pyrex for blanks new [Re: glennnnnnn]
      #5590982 - 12/27/12 10:59 AM

Quote:

Oh. Corporate raiders of the worst kind.




Your average consumer is always going to go for the product that is a few dollars cheaper and is oblivious of quality.

And I have seen glass cookware that actually just broke, not exploded, meaning it wasn't even tempered soda-lime.


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glennnnnnn
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Re: melting pyrex for blanks new [Re: rcdk]
      #5591400 - 12/27/12 03:50 PM Attachment (25 downloads)

You can bet that somebody always makes money!

There's been a sea-change in quality and the pride in making good things that are designed to last.
A hundred years ago the market was always growing, and there was an optomistic confidence. That was when someone saw your plow or ax or shotgun and knew that it was a quality product, and they wanted one just like it.
What we have now is cheap materials and advertising to convince and persuade you to buy what turns out to be a thing that breaks easily or wears out on a schedule of X number of cycles (planned obsolescence!)
The philosophy is that its good for business, because you're a repeat customer, and its also a way to keep those millions of production and assembly workers busy. DO YOUR PART! BUY SOMETHING!
There's something wrong with a business model where the company must always be expanding. Unlike the infinte Universe, here on this small planet everything is limited.

The bright side is that this is a very good time to be one of those people who can make things for yourself. Many ATM'ers are in this more self-sufficient group. When you build your telescope you build it to last, not to throw away in a few months or years.


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KenScharf
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Re: melting pyrex for blanks new [Re: glennnnnnn]
      #5591454 - 12/27/12 04:40 PM

I hope that some ATM'ers with kilns will make some extra blanks from surplus glass (either low expansion or just plan old plate), and see fit to sell them to others at a fair price. Not all of us want to make monster Dob's, and you really need to make a number of good small mirrors to hone your optical skills in order to make a good large mirror. I'd be happy if I could make a good mirror around 12" or so. That's about the largest scope I could use that would be portable and not require a ladder to use.

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dan_h
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Re: melting pyrex for blanks new [Re: careysub]
      #5591484 - 12/27/12 05:10 PM

Quote:

Quote:


The density of 7740 Pyrex is about 2.23 grams/cc where as the density of soda-lime about 2.44gm/cc. If one has a reasonably accurate scale one can use the Archimedes principle to determine the density with sufficient accuracy. In the lab at work, I have a digital scale with a capacity of 15Kg that measures to 0.1 gram, I have used this with mirrors up to 16 inches to measure the density of the glass.

Jon




I took a crack at this with my old, old Pyrex measuring pitchers (I have gram-accurate digital scales), but found that my attempts to measure displacement with kitchen equipment were less precise than required to distinguish the densities (I tried both measuring volume change, and the mass of overflow).

I have a digital luggage scale (suspension hook type) that I will break out to see if I can distinguish the weight change from immersion without trying to measure displacement. It may not be accurate enough though.




I have done this determination without the use of an accurate scale to measure the mass. I set up a balance arrangement where I could immerse the article of interest and measure the balance point along the beam with the article in air and in water. I used an accurate measuring ruler to determine the balance positions on the beam and was able to work out the densities needed. I could detect pyrex from BK7 pretty easily.

dan

dan


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Mark Harry
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Re: melting pyrex for blanks new [Re: dan_h]
      #5591600 - 12/27/12 06:46 PM

Instead of doing a displacement of volume, just calculate volume instead. I used this to identify a pyrex blank that was moulded in a KzFS4 mould with those initials on the glass. I came out to within 3 places of the decimal point of pyrex value---close enough.
M.


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danjones
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Re: melting pyrex for blanks new [Re: Mark Harry]
      #5592018 - 12/28/12 12:13 AM

i'm currently using plate glass in my kiln. its everywhere. i already got a list of ppl who just want me to come get their old tabletops out their basement. i tested the kiln just to see how hot it could get, since i was doing that, i went ahead and threw a mold together and some plate to see what happened. the kiln well exceeded what i need for temp, melting the glass easily along the way. while i did get a rough blank, i didnt anneal it at all so its no good, that wasnt my test. i'm building a ramp/soak controller now to control the firing/annealing stages. so until its done, just melting experiments. i was just wondering if 'pyrex' pie plates would work, but thinking not. thanks for all the feedback.

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KenScharf
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Re: melting pyrex for blanks new [Re: danjones]
      #5592454 - 12/28/12 10:59 AM

Even if those 'pyrex' pie plates are really 'soda' glass they might still make a good blank (as good as plate glass anyway). You just want a source of good quality glass. There is nothing wrong a well annealed plate glass disk for a mirror, at least up to 18" or so in diameter. Port holes are of this stuff and John Dobson has made countless telescopes from them.

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Mark Harry
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Re: melting pyrex for blanks new [Re: KenScharf]
      #5593157 - 12/28/12 07:08 PM

I think that's the key with plate glass- if the anneal is good, you're all set.
M.


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sopticals
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Re: melting pyrex for blanks new [Re: Mark Harry]
      #5593164 - 12/28/12 07:10 PM

Quote:

I think that's the key with plate glass- if the anneal is good, you're all set.
M.




Yup.


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astrobeast1
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Re: melting pyrex for blanks new [Re: sopticals]
      #5593215 - 12/28/12 07:40 PM

Wow ! that,s good new,s for me then . anneal it well, =excellent blank.anyone want a mirror ?

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sopticals
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Re: melting pyrex for blanks new [Re: astrobeast1]
      #5593547 - 12/28/12 11:25 PM

Quote:

Wow ! that,s good new,s for me then . anneal it well, =excellent blank.anyone want a mirror ?




Yup.


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Chuck Jennings
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Re: melting pyrex for blanks new [Re: sopticals]
      #5595610 - 12/30/12 06:22 AM

I'm a little late to the conversation, but a friend and I have successfully fused and annealed a 14" plate blank in our kiln, and figured the blank to F4.3 at the last Delmarva mirror making session. We used Mike's work as a starting point, and modified slightly. Although we have yet to try it, I don't see why borosilicate wouldn't work with an adjustment of the temps. There are some pictures of our project as well as our ramp/soak schedule in the following thread.

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/5138637/page...


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mark cowan
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Re: melting pyrex for blanks new [Re: Mark Harry]
      #5599024 - 01/01/13 01:20 AM

Quote:

Instead of doing a displacement of volume, just calculate volume instead. I used this to identify a pyrex blank that was moulded in a KzFS4 mould with those initials on the glass. I came out to within 3 places of the decimal point of pyrex value---close enough.
M.




Yup. I did this to ID a suspected Zerodur blank (oh, like the color isn't a giveaway - - but they've come in all shades). Measurement and an accurate scale gets to digits.

Best,
Mark


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FlorinAndrei
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Re: melting pyrex for blanks new [Re: danjones]
      #5600135 - 01/01/13 06:49 PM

Dan, how many watts (or amps) are required by the 17" kiln at peak temperature?

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John Carruthers
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Re: melting pyrex for blanks new [Re: mark cowan]
      #5602328 - 01/03/13 03:40 AM

or immerse the suspected Pyrex in vegetable oil, if it 'disappears' it's pyrex (or something with a similar RI).

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danjones
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Re: melting pyrex for blanks new [Re: FlorinAndrei]
      #5607519 - 01/05/13 11:24 PM

hi florin. thanks for the interest. i'd have to go out and look at the label of the kiln, but i'm sure it's requires 30 amps for peak temp topping out at near 2300 degrees. for melting plate glass, it can be just melted enough at 1700-1725 or so. melting broken chunks or strategically cut chunks in a stack, needs more 1800. other substrates like pyrex and others need more, but well within my kiln's max. it needs 230v to operate fully, but requires more technology than the onboard temp control. glass is finicky, and the temp needs to be controlled precisely. i'm working on a ramp/soak controller to exactly control the kiln's temp operation. the ramp up heat and soak times need to be controlled, especially to well anneal the glass and take out any strain, even in the thickest of blanks.

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Babaloo
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Re: melting pyrex for blanks new [Re: danjones]
      #6225748 - 11/30/13 07:18 PM

Boy, you can tell a lot of you guys haven't been doing much of the cooking! The new 'Pyrex' has a greenish tinge to the cookware edges, extremely noticeable. And it is just tempered glass. The real Pyrex cookware (which may be different from the Pyrex used in labware) has no tinge (termed colorless). I think one would be safe in scrounging up a lot of old colorless Pyrex cookware from garage sales and melting it all together (better yet, some old labware.) It would also be advisable to cast/slump a test piece from the molten batch, anneal it, and run it through some heat shock tests to make sure. But if the melt can be mixed thoroughly (stirred?), that might very well negate any slight differences in C.O.E.s of the constituents, if different.

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ccaissie
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Re: melting pyrex for blanks new [Re: Pinbout]
      #6226467 - 12/01/13 07:02 AM

Quote:

A 16 x 3.25 would make a 24 x 1.5?




Interesting. I've got a few of the old yellow monsters.


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ccaissie
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Re: melting pyrex for blanks new [Re: TxStars]
      #6226470 - 12/01/13 07:07 AM

Quote:

Isn't the old way of mixing glass to cast/break/re-cast several times?




I think they melt a raw batch, shatter it, select for homogeneity and correct dispersion, then remelt for greater quality as needed. I've got a 10" piece of BK7 that is "A/PK" and that must've been gone through several times to reach such quality.


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steveastrouk
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Re: melting pyrex for blanks new [Re: ccaissie]
      #6226594 - 12/01/13 09:42 AM

European 'PYREX' IS 100% borosilicate, I used to supply equipment to the UK factory, before it moved to France. I did negotiate a deal to buy broken returns, in ton lots, for around $2000, but when I punted the idea in forums like this, the silence was deafening. I have the actual glass formulation used written somewhere.

LCD monitors have boro glass faces too.


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Napersky
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Re: melting pyrex for blanks new [Re: steveastrouk]
      #6228643 - 12/02/13 09:27 AM

Awesome I hope making optical glass is the next trend for ATMs. The major glass companies have been gouging the community to the max!

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JohnH
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Re: melting pyrex for blanks new [Re: Napersky]
      #6228738 - 12/02/13 10:19 AM

I have a pair of these huge 16" X 3 /14" blanks and a better use of them would be to cut them into 2 1 1/2" blanks.

I found the cost of around $150 to cut without any other work (lapping or diamond generation) quite reasonable


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Napersky
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Re: melting pyrex for blanks new [Re: careysub]
      #6228755 - 12/02/13 10:25 AM

Quote:

You can buy authentic Corning Pyrex 1" rod for $8 a pound (a 4 foot 1" rod weighs 3 lb) from glass blowing supply places:

http://www.waleapparatus.com/catalog.asp?prodid=547940&showprevnext=1

It appears the Pyrex brand name was sold to World Kitchen just for the cookware product line.

http://www.corning.com/lifesciences/us_canada/en/technical_resources/product_...





I would guess that there is quite a difference between optical Pyrex and Kitchen glass which is still manufactured. Only the former was discontinued.


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Napersky
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Re: melting pyrex for blanks new [Re: Napersky]
      #6228778 - 12/02/13 10:34 AM

http://www.newportglass.com/pyrexmkt.htm

"From a distributor and a fabricator perspective, both Newport Glass Works, Ltd. and Newport Industrial Glass, Inc., will continue to offer “Pyrex” parts and sheets from equivalent replacement material. Newport will be stocking and distributing Schott’s Supremax 33 and Borofloat in lieu of “Pyrex”. They will also offer “Pyrex” replacement material in strip form made by other manufacturers."

http://www.matweb.com/search/datasheettext.aspx?matguid=5bb651ca58524e79a5030...


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Napersky
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Re: melting pyrex for blanks new [Re: Napersky]
      #6228790 - 12/02/13 10:41 AM

Apparently Corning sells a ULE that's better than Pyrex and in bulk.

http://www.pgo-online.com/intl/katalog/ule.html


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careysub
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Re: melting pyrex for blanks new [Re: Napersky]
      #6228808 - 12/02/13 10:49 AM

Quote:

Quote:

You can buy authentic Corning Pyrex 1" rod for $8 a pound (a 4 foot 1" rod weighs 3 lb) from glass blowing supply places:

http://www.waleapparatus.com/catalog.asp?prodid=547940&showprevnext=1

It appears the Pyrex brand name was sold to World Kitchen just for the cookware product line.

http://www.corning.com/lifesciences/us_canada/en/technical_resources/product_...





I would guess that there is quite a difference between optical Pyrex and Kitchen glass which is still manufactured. Only the former was discontinued.




Laboratory Pyrex is still manufactured, and actual Corning Pyrex rod would be this same material.

This is exactly the material wanted for mirror manufacture since it has the very low thermal expansion property (one does not want a beaker of acid shattering from thermal stress).

The discontinuation of the production of Pyrex mirror blanks would be a separate issue.

The original kitchenware borosilicate Pyrex with the same low thermal expansion was discontinued when the tradename for that product line was sold to World Kitchen in the late 1990s. World Kitchen sells cheap soda lime glass that has been tempered through a heat heating process under the name "Pyrex" (essentially the same as that produced by Anchor Hocking).

http://www.consumerreports.org/cro/magazine-archive/2011/january/home-garden/...

World Kitchen makes a business out of buying famous high quality kitchen brands, then selling cheap knock-offs under that old famous name.

They did this with Magnalite cookware also, replacing the original magnesium with cast aluminum; and with Revere Ware, replacing the clad copper disk which provided excellent heat distribution with thin copper plating which quickly comes off in a most unsightly manner.


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TxStars
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Re: melting pyrex for blanks new [Re: Napersky]
      #6228926 - 12/02/13 11:37 AM

One could also remelt Zerodur sheets.
http://www.capovani.com/iinfo.cfm?itemno=105019


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kfrederick
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Re: melting pyrex for blanks new [Re: TxStars]
      #6228931 - 12/02/13 11:40 AM

http://www.pottersweb.net/index.php?ad&cat=kilns

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Napersky
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Re: melting pyrex for blanks new [Re: careysub]
      #6229231 - 12/02/13 02:06 PM

Quote:

Quote:

... There's something about Pyrex that I don't quite understand: how could a product with such usefulness and value just be pulled out of production?




You never saw a product with an established brand-name be replaced with a cheaper substitute trading on the original's reputation?

This is extremely common, I would say the rule rather than the exception, when a brand-name is sold to another company that did not build up the brand's rep. This is what happened here when Corning sold off its consumer product line to World Kitchen.

Quote:

I think that the answer is more complicated than just business buying and selling, and may involve the EPA and other agencies.




Why would you think this?

Maximizing profit is more than sufficient explanation.

NB: Just within the realm of cookware I can cite several examples of former prestigious brands being debased with cheaper knock-offs.

World Kitchen not only did this (apparently) with Pyrex cookware, they also did it with Magnalite - a premium brand of cast magnesium cookware (hence its name) dating from 1934 now consisting only of cheaper and heavier cast aluminum.

Revere Ware once consisted of premium stainless steel pots clad to a disk of copper for rapid heat distribution. The pots today have the same appearance, but the "copper bottom" is now thin plating for show, which quickly wears off in an unsightly manner.

West Bend was once a brand of cookware that produced a very popular and nifty electric wok (famous for its red enamel exterior) with a thermostatic control. I used mine for decades until it finally wore out, and bought a new "West Bend" wok, to find that the "control" was now just a potentiometer and the "temperature" scale on it meant nothing. After burning the first dinner I tried to cook in it, and then have it shed screws and nuts into my garbage disposal, destroying it, I threw the worthless thing out.

Regal has been cheapening its own classic line of cast aluminum cookware, with ever thinner and more poorly cast products.

This is a very, very common practice. U.S. made real premium cookware is mostly a thing of the past it seems.





Corporate America seems today to be run by Frauds and Crooks. Executives without conscience who deceive the consumer.


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Napersky
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Re: melting pyrex for blanks new [Re: Napersky]
      #6229266 - 12/02/13 02:23 PM

World Kitchen, I've seen their junk, I believe their cutlery is made in China. It doesn't surprise me they would lie and say Corning swapped kitchen borosilicate Pyrex for *BLEEP* soda glass!

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careysub
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Re: melting pyrex for blanks new [Re: TxStars]
      #6229406 - 12/02/13 03:14 PM

Quote:

One could also remelt Zerodur sheets.
http://www.capovani.com/iinfo.cfm?itemno=105019




Are you sure that you can?

I'm not saying you can't, but Zerodur is a two-phase glass-ceramic composite and I have always supposed that special temperature cycles were necessary for production to produce the desired properties.


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kfrederick
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Re: melting pyrex for blanks new [Re: careysub]
      #6229839 - 12/02/13 06:07 PM

Those would make nice 10 inch blanks Get them water jet cut . And generated .

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kfrederick
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Re: melting pyrex for blanks new [Re: steveastrouk]
      #6232849 - 12/04/13 08:22 AM

Quote:

European 'PYREX' IS 100% borosilicate, I used to supply equipment to the UK factory, before it moved to France. I did negotiate a deal to buy broken returns, in ton lots, for around $2000, but when I punted the idea in forums like this, the silence was deafening. I have the actual glass formulation used written somewhere.

LCD monitors have boro glass faces too.


Sounds good A dollar a pound Any one interested I can store it and Steve can bring it over

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