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Old 03-31-2005, 11:22 PM
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Dave, great info on lithium. Another book I'll have to find I guess (Volk). Interesting that the small ion actually makes the glass more dense and more fluxed. Good to have an actual reference rather than what I think I remember someone saying one time. ("Don't trust half of what you think!" and maybe less of what you remember!)
As a side, I always liked my batch formulas with a percentage of magnesium from dolomite better than straight calcium. Interesting to see this compared to lithium. Magnesium containing batches seemed more even in their softening than with calcium only, which makes glass harder on the cold end and softer on the hot end. Some high calcium glasses have seemed rather sudden in softening when heating.
Nick was a smart man. It seems he included lots of non-essential but very desirable components in the SP batch. Zinc for colorant solubility, lithium for durability, density, and ease of melting, a small amount of fluorine which helps with the phosphate opals.
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