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Old 11-05-2003, 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: 22,269
Pete VanderLaan is on a distinguished road
It is true that it is a sweet squeezing glass. I think the great advantage to making it yourself is that if you make an unoxidized form of this stuff- leave out the nitrates, that while harder to fine out, if you always off-load from the mix what you want for color and then add nitrates for the clear part so you can't ever have incompatibility even if you make a mistake at the scales.

Back with your adjusting of the formula, and your decision to only mess with the soda just needs a brief observation. If the moisture content of the silica is 1 percent, that means that you are off one pound silica per 100 lbs loaded, which is not insubstantial. Usually when I am fine tuning a formula, I always do it with the silica and usually it is less than 100 grams per 100 pounds batch to move the formula to where I want it, unless I have seriously screwed up. In general, I don't like to mess with the potassium/sodium ratios at all when adjusting. The silica is very powerful as an adjusting chemical and it can be moved with very little recourse. This is never mentioned in any books on the subject and Soda is always referred to as the holy grail for adjustments. I advise you to not use the soda for that purpose or at least be cautious with that.
63 grams of soda in 15 lbs of glass is quite a bit and is probably driving the expansion up about one full point. That may be a good target amount when you want to push this stuff around. Either that or adjust the silica about the same amount..

It is by the way really heartening to me to see some of you playing in this particular sandbox. There are so few of us now and it really makes me feel that my efforts here at craftweb are worth it just from the pure educational aspects.
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