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Old 04-03-2005, 05:36 PM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
 
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 20,100
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well, the curiosity I run into, and I agree that neither a pull test or a dilatometer test tell the definitive story BUT when I do a ring test and I get a slight gap, it tells me that the inner glass needs a higher expansion. If in 100 lbs of the inner glass, I add about 100 grams of sodium, or another of the alkaline fluxes, the gap usually closes. That is true in either opaques or in transparants. What it doesn't say as a test again applies to viscosity and it is grossly obvious that the viscosity of a soda lime clear is way way higher than it is in a fluorine opal. My opals actually melt at about 1975-2000F which really tells the viscosity difference in a heartbeat. Now I can get these two totally dissimilar glasses to do great in a ring test, to give me a consistent readout in a dilatometer, give me terrible pull tests have totally different softening point but saw like a dream and grind like a dream, never break in blownware, but check if there is too much of the opaque in relation to the transparant soda lime present. That is as in 2 inches thick or so. At one point I was making some weights that were about four inches across. I would take two big gathers of the fluorine cased in clear and they would crack. If I used a gather of clear, then the fluorine and then the clear, they were perfect and never gave any trouble. If I blew those glasses together, they never gavwe me any trouble. I could grind and I could saw and they never gave me any trouble. I varied annealing schedules and it never affected a thing. I don't know what the deal was.

Now I know that the fluorine crystals are growing, collapsing and regrowing as the glass ages but it's viscosity doesn't seem empirically to be changing much. I suppose I could continually check it each day for differences, I just never have. I am simply observing that as the density of the opacity goes away, the viscosity doesn't seem to go along with the density loss.. When I make color rod or frit, I capture the density of it usually about ten hours after the melt and I have not had occasion to watch its characteristics deteriorate in a measurable way/ ( nor do I care to)

Chuck Savoie used to say to me, and it really applied to cad sel opaques particularly when we were screwing with some of the old Thuringen formulas,, "Sometimes it's so far out, it's in." The information is so conflicting.

Cold comfort.
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