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Pinbout
Postmaster
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Reged: 02/22/10

Loc: nj
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
Carpal Tunnel
*****

Reged: 02/18/11

Loc: Rancho Cucamonga, CA
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
Carpal Tunnel
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Reged: 02/18/11

Loc: Rancho Cucamonga, CA
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
Carpal Tunnel
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Reged: 02/18/11

Loc: Rancho Cucamonga, CA
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
sage


Reged: 10/20/09

Loc: San Diego, CA
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
Carpal Tunnel
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Reged: 02/18/11

Loc: Rancho Cucamonga, CA
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
Carpal Tunnel
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Reged: 02/18/11

Loc: Rancho Cucamonga, CA
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
sage


Reged: 10/20/09

Loc: San Diego, CA
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
super member


Reged: 11/13/10

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
sage


Reged: 10/20/09

Loc: San Diego, CA
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
member


Reged: 12/16/12

Loc: South Fla
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
Carpal Tunnel


Reged: 12/10/07

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
Vendor
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Reged: 09/05/05

Loc: Northeast USA
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
super member


Reged: 09/26/12

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
member


Reged: 12/16/12

Loc: South Fla
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
Vendor
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Reged: 09/05/05

Loc: Northeast USA
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
professor emeritus


Reged: 03/28/10

Loc: New Zealand
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
super member


Reged: 09/28/10

Loc: leicester england
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
professor emeritus


Reged: 03/28/10

Loc: New Zealand
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
member


Reged: 01/18/11

Loc: Townsend, DE
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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