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-   -   John Croucher's class at Penland (http://talk.craftweb.com/showthread.php?t=12307)

Josh Bernbaum 04-30-2019 02:02 PM

John Croucher's class at Penland
 
2 Attachment(s)
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..

Pete VanderLaan 04-30-2019 02:25 PM

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.

Scott Novota 05-01-2019 10:43 AM

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.

Pete VanderLaan 05-01-2019 05:45 PM

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.

James Burts 05-01-2019 06:18 PM

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 (Post 143984)
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.


John Croucher 05-01-2019 07:33 PM

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.

Jordan Kube 05-01-2019 09:06 PM

The class was really wonderful. I've mostly had access to a polarimeter since I first learned how to make trident seals in your class, Pete, and I can't imagine making color without one. I think the point was to show the way with a pro tool. The ring test is easy enough to fool around with and make on your own in the studio. When I worked for Ed Skeels he had a nice cylinder mold and some dial calipers and knew quite a bit about what his glass was doing. It would have been hard to teach the class like that though. John and Mark did a really good job of teaching everyone how to be their own guide when making glasses. I can't imagine it being taught any other way. The class had glass makers of varying experience but the great thing about it was there was something for everyone.

Nice pics Josh. Look at those colors!

Pete VanderLaan 05-02-2019 07:09 AM

Initially, it appeared that Nick had called me to see if he could borrow my polarimeter which would have been fine but by the time we had connected, he told me he was being lent one by Strainoptics. I didn't realize that "Lent" meant "rent" and at the $1600 dollar loan for two months, that's really a lot of money. I would have rented him mine for that in a heartbeat.

Any and all of these methods for determining strain are valid in my mind and the pull test starts you down the road immediately to knowing whether your day is ruined BUT none of them in these existing scenarios is going to hand you a definitive "go- No Go".

When I was testing the Marko Blanko, i had work that was showing no signs of strain but broke up a few months later. That was discouraging. I've lost work to a variety of events, not the least of which was questionable annealing.

I tend to think that both John and I own that tool because we both made color rods. I don't think I would own one if I hadn't done that. Too much money. Even my crusher now runs $7,000 dollars.

It certainly is the case that the ring test rquires seeing more than a few ring tests but at the same time, normally, if the ring survives the saw, the fit is usually adequate right then, yet the gap will tell you what to do next in fine tuning. That's how I work in general.

Mark was the real curiosity in that he never measured anything to my knowledge. He just had this Yoda way of looking at the colors in the earlier days. Now, to the best of my knowledge, he never laminates color at all. It's all monolithic and what needs determining most is the annealing cycle. His big issue has long been durability.

I do think that a decent machinist could build the tool. The proof would certainly be in the pudding and I do think the tool is necessary to own if you're going to make and sell colored glass.

Jordan Kube 05-02-2019 07:55 PM

There were plenty of smart people in the class looking at that polarimeter thinking," I could probably build that". I hope they do.

Pete VanderLaan 05-02-2019 08:50 PM

Very nice tool and given how few people actually would really use one, It's understandable why it is as pricey as it is.

Again, I have all three tools. I use the ring test for my own work. Fast and immediate.

Pete VanderLaan 05-03-2019 03:58 PM

I talked to Nick today and it wasn't all that bad. The rental was $650 dollars for a shorter period. Nick wants to measure a bunch of different stuff that has been drifing around the shop. It also turns out that Tom Littleton owns one as well. I think that goes back to the color classes in New Mexico.

Greg Vriethoff 05-05-2019 01:43 PM

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A friend of mine that I met blowing glass in LA used to work for one of the large auction houses. Needless to say he managed to amass a large collection of knick-knacks, and detritus from estate sales, etc. When items wouldn't move at auction they'd offer first dibs to employees at a discount. I will be eternally jealous of the Fritz goblet he picked up for $50. He also has a Nick Labino.

He also ended-up with this. I took these pics while we were checking some small rondels he made for a stained glass artist.

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