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Tom Fuhrman
03-25-2012, 09:13 AM
Old guy here looking for new answers: How do you check a 12" cube of cast glass for proper annealing? Especially if it is a deep color and you can't get any light to pass thru it. MY polariscopes don't accomodate this. I know all the annealing schedules for items like this but does that really make it foolproof?

Pete VanderLaan
03-25-2012, 12:38 PM
Answer. "No". It has to be made with a witness piece in clear.

George Tessman
03-25-2012, 12:43 PM
sphygmomanometer usually works for checking my stresses

David Patchen
03-25-2012, 01:09 PM
There are no gaurantees since a clear block won't be exactly the same anyway. Why not take the most conservative schedule and add an extra week if you wanna be super cautious?

Steve Stadelman
03-25-2012, 01:54 PM
With a 12" cube the margin of error will be more like adding a month or two ;)

Ben Solwitz
03-25-2012, 03:18 PM
The clear block is just supposed to give you a lower bound David. You keep lengthening the annealing until a clear block comes out ok, and then you know that your color piece needs at least that long, and quite possibly longer. If it doesn't work for clear, it's not going to work when you complicate it with color. Much cheaper to have the first few fail in clear while you make adjustments.

Allan Gott
03-25-2012, 04:26 PM
sphygmomanometer

....OK.......I'll bite.........a WHAT???

George Tessman
03-25-2012, 04:29 PM
....OK.......I'll bite.........a WHAT???

a blood pressure cuff...lololo

Pete VanderLaan
03-25-2012, 05:57 PM
George is showing post gluteal sting.

The clear witness won't be exactly the same but if the formulation is similar you will not do better than that method.

David Patchen
03-25-2012, 06:01 PM
The clear block is just supposed to give you a lower bound David. You keep lengthening the annealing until a clear block comes out ok, and then you know that your color piece needs at least that long, and quite possibly longer. If it doesn't work for clear, it's not going to work when you complicate it with color. Much cheaper to have the first few fail in clear while you make adjustments.

I understand this but who would bother when there are great resources for annealing schedules available--especially considering each clear test would take forever

Pete VanderLaan
03-25-2012, 06:18 PM
Remember the question was whether an annealing schedule would make it foolproof. Virtually all annealing sources make assumptions about the viscosity of the glass involved which in turn tells the story of the strain. . There are virtually thousands of glasses. I think the best stuff out there is Graham Stone's "The Schedules" but it is not a book in wide circulation. Joe Peiffer does have it for sale and it is well worth owning. I guard my copy carefully. Assuming any of these publications will always be out there is not a good plan. I said elsewhere that books printed ten years ago are unavailable. Volf, arguably the best book on the chemistry of glass ever written was only in print for about three years in 1981. Joe brought it back and it's expensive. It's also priceless. When it's gone you will not see it again. When Henry goes, as will we all, I don't know what will become of Glassnotes. I am going back and working on my book and hope to have it ready for editing by the time my color class happens next year, which by the way is full!

Tom Fuhrman
03-25-2012, 07:47 PM
[I] wasn't asking so much for my own production but have had collectors/friends ask me about pieces that are on the secondary market. I question if some of the big castings that have been produced over the last 30 years have a lot more stress in them than they should. I know I saw a lot of stuf go thru a very short anneal schedule when I was at the Int'l Glass Symposium many years ago in the Czech Rep. that was very thick and done by some of the biggest names in the glass world. I wonder how many other times this happens. Howard Ben Tre, David Ruth, Susan Gott, and many others come to mind that have been doing some huge stuff for many years.I've also seen demos at other conferences where large castings were produced and offered less than 36 hours later at their fund raising auctions. I hope they've stayed together./I]

Eric Hansen
03-25-2012, 09:51 PM
Throw it in a deep freezer for a few days. If it makes it....:)

Rick Wilton
03-26-2012, 10:12 AM
they are selling Stones book on warm glass if anyone is looking.

http://www.warmglass.org/servlet/the-1553/Firing-Schedules-for-Glass/Detail

Pete VanderLaan
03-26-2012, 11:11 AM
Throw it in a deep freezer for a few days. If it makes it....:)
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That's the catastrophic approach and you don't learn anything about the piece beyond breaking it.

Pete VanderLaan
03-26-2012, 11:16 AM
they are selling Stones book on warm glass if anyone is looking.

http://www.warmglass.org/servlet/the-1553/Firing-Schedules-for-Glass/Detail
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The site of Joe Pfifer's in "Schools and books" hawking Volf has the book as well. Joe in fact got the reprint rights to it and is why it is on warmglass. He took the risk. Reward Joe.

Ted Trower
03-27-2012, 07:36 PM
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That's the catastrophic approach and you don't learn anything about the piece beyond breaking it.


So my question here is why should this last 60 degrees F make so much difference?

Pete VanderLaan
03-27-2012, 07:48 PM
well, the thought isn't really complete Ted. Nick Labino would indeed put stuff in the freezer but then brought it out and ran warm water over it. Nick was pretty tough on things. I think that just running hot water over it will make a lot of stuff let go. Solids are pretty resistant to change though. The bigger the weirder. Ben Tre just regularly sold the stuff cracked which I have always thought to be pretty lame.

Tom Fuhrman
03-28-2012, 09:00 AM
well, the thought isn't really complete Ted. Nick Labino would indeed put stuff in the freezer but then brought it out and ran warm water over it. Nick was pretty tough on things. I think that just running hot water over it will make a lot of stuff let go. Solids are pretty resistant to change though. The bigger the weirder. Ben Tre just regularly sold the stuff cracked which I have always thought to be pretty lame.

and what kept it from cracking even more?
In answer to my original question, I guess there is no scientific device or procedure that is available to actually detect these problems. Prior to 1950, then I presume that most things over 4" thick were probably not adequately annealed as they had few controls to do a gradual turndown of the temps and have a real schedule for annealing. That makes some of the early 20th century large Italian stuff even trickier to have survived and with lots of colors as well.

Pete VanderLaan
03-28-2012, 09:58 AM
and what kept it from cracking even more?

**********
"when you can take the pebble from my hand it will be time for you to leave grasshopper."

David Patchen
03-28-2012, 10:23 AM
**********
"when you can take the pebble from my hand it will be time for you to leave grasshopper."

I'm a sucker, I'll bite.

When work cracks the internal stress is relieved. The crack will only travel to the degree that the stress exceeds the strength of the glass. Once the stress that is greater than the strength of the glass is relieved the piece will not continue to crack.

Gimme that pebble!

Pete VanderLaan
03-28-2012, 10:51 AM
I find that once glass starts a crack it just keeps on going. It just takes its sweet time. Can you say windshield?

Quote is from "Kung Fu" with David Carrradine back around 1970 from Master Po in dat ol' Shaolin temple.