View Single Post
Old 07-13-2002, 11:59 AM
Pete VanderLaan's Avatar
Pete VanderLaan Pete VanderLaan is offline
The Old Gaffer
Join Date: Apr 2002
Location: Chocorua New Hampshire
Posts: 21,968
Pete VanderLaan is on a distinguished road
It only takes about 150 Grams of Sodium to push the C.O.E. around a few points in 100 lbs of batch, so no, it doesn't affect stability. It can simply make colors that fit marginally not fit at all.
The first time i ran into this, I was melting a copper ruby that fit Sp87 fine. I would charge on sundays and everything was cool, filling both pots. On Wednesday I would be a bit short on the red and instead of preheating the furnace, I would chuck the red in and turn it up. It would come from the same batch mix that I used on Sunday. Any glass made from the second melt would crack. I began a logic elimination process and started measuring the glasses. It was way way off melted cold.
So then I did a tracking on the glasses melting at fixed temps and measuring the coe of each glass. That yielded the 94-98 range I referred to.

You can do this with other marginal fits as well. Opaque yellows and reds, and transparant reds and yellows can be made to go out of "fit range " if you work them long enough on the pipe. It takes about eight hours. Peiser had this problem back in the Wisteria series. Fussy stuff.
Reply With Quote