Thread: basic steps
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Old 11-09-2019, 10:59 AM
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Pete VanderLaan Pete VanderLaan is offline
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Join Date: Apr 2002
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To address Sky first. As time has gone by I feel that craftweb has become a place that people want to use to supply the answers but it seems to spend less and less time learning about the material. In that capacity, I want to see people making a genuine effort to understand things that affect their studios. I certainly won't always be here. Nick Labino used to have the same attitude I have been developing more slowly. If he thought you had been working at it, he was more open. If not, he had plenty of stuff he wanted to get to.

For Paul, the issue of colorants in glass has really not been addressed much as to when they start to cause expansion and viscosity problems. There were two studies done back around 1920 and the first was english and Turner, developing basic linear expansion factors for the primary additives for clear glasses and they used a 19C-300C range to develop the factors. The other testing was done by Winkleman and Schott and that was for the enamel industry and it did indeed deal with colorants but in a 19-200C range yielding rather differing results. They were conflated unfortunately in an article by Paul Manners in "Glass" back in 1974 and that was canonized in Glassnotes 3 by Henry Halem. Henry withdrew that material for the Glassnotes 4 edition. You can still develop reasonable expansions using Appen as your guide and by approaching formulation through Mole chemistry which is what Mark does.

As to my old formulas, as I said , they work, so does SP87 but don't cast with it and that would be true of both glasses for differing reasons. As I said, mine needed alumina but it has other issues as well. The glass I started off with that I quickly altered was Dudley Gibserson's formula which has enormous problems.

When you really look at it over a long period of time (50 years) , actually very few formulas have come out of private shops to be consumed by studios. Starting with something like SP87 or it's color base- the same stuff with no nitrates and no antimony is what people do. That's really limiting. Calcium and sodium really make poor colors. A basic trip into Sam Scholes book shows you what the different additives may do and it does seem to me that the basic parameters for formers, modifiers and stabilizers are available readily. I like to see people dinking with them . I have lost my enthusiasm however for just supplying answers. On four occasions I have offered classes teaching this and a few of the individuals took it up. One was ballsy enough to simply take my formulas and make color rod out of them and to sell it , undercutting my own prices for ones I would make. That was a lesson for me in learning what I could and couldn't share.

You can note that in Ed Pennybaker's question, I answered it far more completely that I have others. The reason was simple. Ed was trying to do it. I didn't give away how to make those glasses, in reality they have lots of things that often go wrong, but I did lay down some pointers that took me some time to figure out. In henry Helmers batch book, one can deduce quantities of colorants for formulations by digesting the thousands of formulas in there. The caution needs to remain that these guys simply never considered mismatch because they never combined glass types. The private shops on the other hand want to throw everything they have into a piece. That's problematic.

In many instances, I get private messages asking for this sort of stuff and inevitably refer the writer to craftweb and posting the question publicly. That allows everyone to see what is being considered. I do not ever ignore a question. I do find it interesting that I get critiqued for not just supplying the answer.
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