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Old 05-01-2019, 06:18 PM
James Burts James Burts is offline
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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.


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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