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glennnnnnn
sage

Reged: 10/20/09

Loc: West Coast High Desert

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
Post Laureate

Reged: 12/02/04

Loc: Hockessin, De

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
sage

Reged: 09/13/10

Loc: Whitefield, Maine

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
member

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
Post Laureate

Reged: 04/01/08

Loc: Lovettsville, VA

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
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
Post Laureate

Reged: 05/10/05

Loc: Central Texas

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
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
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
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
sage

Reged: 12/21/11

Loc: Sri Lanka

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
Post Laureate

Reged: 04/01/08

Loc: Lovettsville, VA

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
Vendor

Reged: 09/05/05

Loc: Northeast USA

Re: melting pyrex for blanks new

[Re: Dave O]
#5586697 - 12/24/12 06:47 AM

Precisely
M.

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danjones
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
sage

Reged: 10/20/09

Loc: West Coast High Desert

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
Postmaster

Reged: 06/16/04

Loc: San Diego and Boulevard, CA

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
member

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
Post Laureate

Reged: 02/22/10

Loc: Montclair

Re: melting pyrex for blanks new