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Old 04-30-2019, 01:02 PM
Josh Bernbaum Josh Bernbaum is offline
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John Croucher's class at Penland

It was a really fun time, great group of folks, and we did lots of small melts. Four of Pete's 7" pots in a sliding top-door gas furnace. Focus on phosphates, some cad sels, and some misc. other ionic colors. I brought down some of my gold sands and a bit of Pb and we did one phosphate gold pink in Nick Fruin's electric kiln with a clay pot from China. We thought it didn't work at first, was just white, then after someone reheated it a few times it struck really nicely to an opaline pink. John showed us how he is most fond of the trident-seal test and how to do those with an (expensive) polarimeter. Jordan and James and Eric were the other craftweb folks there, and Kenny stopped by once or twice too. No women unfortunately, a real sausage fest. Penland was a great place for a class like this. Heard it was the longest waiting-list for a class in Penland history, and to think I was concerned it wouldn't fill at first. I think John had a good experience and was fond of the group. Unfortunately his son Luke, who was supposed to be a co-teacher, couldn't get a visa approval to travel. So we got Mark Peiser to fill in instead, not too shabby of a replacement. Mark said he thought it might have been the best class he'd been a part of. We got to visit his studio on the last day which was a real treat. I'm motivated to fire up my color furnace again now..
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Last edited by Josh Bernbaum; 04-30-2019 at 01:20 PM.
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Old 04-30-2019, 01:25 PM
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Pete VanderLaan Pete VanderLaan is offline
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John Called me yesterday and we chewed the fat about the class and the different ways to approach it. He said he might be inclined to teach again in about 30 years. I know the feeling.
He is on his way back to Auckland now. I had thought he was going to move up here when Gaffer relocated in Portland but he indicated that he was really retiring. I know that feeling too. He might come back to the States if GAS gets held at Corning again. I also know that feeling. It's indeed too bad that Luke could not get the VISA. Under this administration it is not easy to do. I know Gaffer had real difficulties bringing some of their experienced people up here. John is still looking around for bar rollers.

You are all fortunate to have gotten to know him at all. He will really be known for his contributions to color in the future which is obviosuly true for Mark as well. Eric Truleson was in that class as well./ He spent a year here with me doing color and I will be most interested in his take on it. John also mentioned Jordan. I'm glad it went well.
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Old 05-01-2019, 09:43 AM
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Scott Novota Scott Novota is offline
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That was a bummer about Luke. I was planning on trying to put him up down here in pensacola when he came for an extended visit.

Maybe he can get to the states once we have an election.
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Old 05-01-2019, 04:45 PM
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Pete VanderLaan Pete VanderLaan is offline
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so, I've been asking myself a question all day and I've asked John and one of my students who took the class. It's pretty straight forward:

If we utilize the Hagy seal to make a sample indicator for differences in L.E.C., we need to recognize a few things: The seal is a sensitive sample that needs to be processed for interpretation in a really expensive tool, the Strainoptics Polarimeter, That tool cost me $2,000.00 dollars almost twenty years back. John has one and Penland borrowed one from the company for the class. It measures degrees of retardation very precisely and those variants can be converted into math differences in the expansion coefficient quite accurately.
So, John has it, I have it and I assume Penland is returning the borrowed one.

So what does the student do who wants to use hagy seals? What tool will accurately measure the retardation of light in the sample?

I taught the Hagy Seal and I taught the ring test and I taught the dilatometer. All of these tests are squishy but if one thinks about them, they should all be pointing in the same direction. Any time that mismatch tests are done, that should be the case.
What I want to know is that barring the possession of the Polarimeter, what are the other ways of using that seal? I can tell you that any sample, either Seal or ring is very far off that the sample will not survive.

I'm not trying to piss on the class at all. All accounts I've heard is that it was fabulous and John is a dear friend. I just want to know, since the Ring and pull tests were not pursued, how does one proceed? My belief is currently that the more methods, the better. No one method seals the deal.
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Old 05-01-2019, 05:18 PM
James Burts James Burts is offline
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Pete--
I think you're quite right. The Hagy seal is a great tool IF you possess the Strainoptics Polarimeter. Without that tool, the Hagy seal isn't much use.

There were several of us at the class that are interested in seeing if it would be possible to build our own version of the Strainoptics unit. From information available online, it seems like it should be possible. The difficult bit will be getting the thing reasonably accurately set and calibrated. If that doesn't work out, then what I heard is that the going rate for a new unit from Strainoptics is $3,600.

Apparently, Strainoptics allowed Penland to rent one for a month, but it's costing them quite a bit (I think I heard the number $700 tossed around as the cost to rent a unit for a month.)

We did discuss the ring test in the class, but you are correct that the class didn't actually perform a ring test on any of the glasses we melted. If this class were to be taught again, perhaps the students might be encouraged to make some ring test samples as well as the Hagy seals--- since the ring test doesn't require specialized tools that shouldn't already be in a glass shop.

I understand John's reasoning to prefer the Hagy seal for his environment. It's the most expedient means to ensure the product Gaffer is producing is all compatible and that mistakes weren't made in batching. However, his needs and pressures are different than that of many glass studios. Being comfortable with a compatibility test that doesn't require an expensive uni-tasking tool is certainly important for most studios. The ring test certainly has it's issues (but everything does--- no free lunch and all), but I think has its place.

--James--


Quote:
Originally Posted by Pete VanderLaan View Post
so, I've been asking myself a question all day and I've asked John and one of my students who took the class. It's pretty straight forward:

If we utilize the Hagy seal to make a sample indicator for differences in L.E.C., we need to recognize a few things: The seal is a sensitive sample that needs to be processed for interpretation in a really expensive tool, the Strainoptics Polarimeter, That tool cost me $2,000.00 dollars almost twenty years back. John has one and Penland borrowed one from the company for the class. It measures degrees of retardation very precisely and those variants can be converted into math differences in the expansion coefficient quite accurately.
So, John has it, I have it and I assume Penland is returning the borrowed one.

So what does the student do who wants to use hagy seals? What tool will accurately measure the retardation of light in the sample?

I taught the Hagy Seal and I taught the ring test and I taught the dilatometer. All of these tests are squishy but if one thinks about them, they should all be pointing in the same direction. Any time that mismatch tests are done, that should be the case.
What I want to know is that barring the possession of the Polarimeter, what are the other ways of using that seal? I can tell you that any sample, either Seal or ring is very far off that the sample will not survive.

I'm not trying to piss on the class at all. All accounts I've heard is that it was fabulous. I just want to know, since the Ring and pull tests were not pursued, how does one proceed? My belief is currently that the more methods, the better. No one method seals the deal.
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Old 05-01-2019, 06:33 PM
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John Croucher John Croucher is offline
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I think what I would do first with a trident seal test, if I only had a polariscope, is make a seal using all three canes out of the same master glass clear, anneal those and then see what zero strain looked like. Then I would compare that trident seal to a mismatch test using two outer canes of whatever you were testing, against the same clear master glass in the center. If the center cane was showing the same shade of light grey as the first test then there is no strain, no mismatch. If the center cane is much lighter, whiter, brighter and not at all the same shade of pale grey, then strain is showing up. To find out how much and whether it is showing tension or compression, then there is the ring test, thread test or chip test on a strip of sheet glass (made out of your master clear).

The chip test can indicate which way the strain is going by bending the master clear sheet strip either way. Stretching or compressing the chip indicates the extinguishing of the brightness.

This is what Bullseye uses. It objectively gives you a handle on how much strain but only by a lot of comparative experience. The same goes for the ring test. The ring test is good for indicating tension or compression, but not good giving an objective assessment of the degree of strain without a good deal of experience. Furthermore, getting the two glasses to be of equal thickness in the ring test is not easy and that is very important to achieve an accurate assessment.

The thread test is only indicative if comparing glasses from the same family, with similar viscosities, Young's modulii, surface tension, emissivity etc. and again, thickness of the respective glasses.

Unfortunately the dilatometer doesn't provide you with comparative strain points, although, granted, it does yield deformation and Tg temps. It does give objective LEC's though, up to the deformation temp, although even the most expensive dilatometer (upwards of $30,000) doesn't give outputs any more accurate than +/-1 points at best. The bottom line though, is that the dilatometer doesn't reveal helpful mismatch viscosity data.

If you were melting your own color and wanting to get glasses compatible, then repeated melts would eventually yield you a trident seal that showed no strain under your polariscope, as you adjust the chemistry. If you were repeatedly doing this for lots of color then a Strainoptic polariscope cuts lots of corners and starts to look like good value.

Last edited by John Croucher; 05-01-2019 at 06:37 PM.
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