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Old 10-09-2019, 11:47 AM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 21,490
Pete VanderLaan is on a distinguished road
I have read both SP87 and my own clear on a dilatomoter and SP87 has really been remarkably consistent over the decdes. I engineered my clear to match SP87 at Tom's initial request and it sits dead on. Using the clear cane from SP87, which I've harversted over the years and kept each harvest with notation, that was applied to Hagy seal testing of other glasses. Both John C and I took the same approaches and found the retardation of light to indicate a 94.1 on the Sys 96. That was coupled up to a ring test done using the SP87 and the glass in question. In that case, I could not achieve any result without breaking the sample using a saw and had to do a live ring test getting the sample off a hot blowpipe which is a good trick but it works. Even the Hagy seal is dicey given the mismatch. In no event could I get the ring test to survive on the saw which is a major criterion for reading the mismatch. Anything over about 1.8 has issues.
So, I like my indicators all pointing in the same direction and they did, the dilatometer being the one that does not compare, it just measures. I normally run a dilatometer three times in testing with a fresh 4.000 sample in each run. I do that from 19-300C. The tool is made of quartz with a quartz pushrod. The cane is meticulously kept at 4.000.

Finally, you can see the results in blown ware as well as paperweights. Pieces break up. It frequently happens when the surface tension is messed with. That freqently occurs with opaque color rod as well when sawn. That's telling. At 1.5, they don't unless there is some other issue, thickness being one.

After doing it for decades, you get to where you can see what's up.
I have really never thought that Spectrum tested or really cared about field measurements. How a company could make two clear glasses, incompatible with each other was always rather telling to me.
I have never cared for the methodology used at Uroboros to read strain. It's a pair of slide sized pieces laid side by side and fused together and then read in a polarized screen. I do get a great sense of mismatch if the glass in question is melted inside of a clear chunk. That glows but I can't convert that to an actual number.

I don't spend my time on this stuff these days. When I was making rod, I did. I don't mind throwing rocks from off in the corner though.
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