CraftWEB Hot Glass Talk

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Pete VanderLaan 11-08-2019 03:26 PM

basic steps
I'll keep this brief but I want to stress something I do keep mentioning:
You really need to be able to make a good clear formula before you can expect to make a good color formula.

Using SP color base is not a panacea for a color formula. Croucher I think ran nine bases, I ran five or six and each was engineered for the colors and additives going into the goop.

The formula listed recently of mine was a glass I derived back around 1976. I messed with that basic stuff over a number of years but finally set it aside for better glass. It really wasn't until I wrote formulas for Spruce Pine about four years back that I came to glasses I really feel settled with. So keep in mind, neither calcium or sodium are your friends, they're just cheap. Fortunately they are all quite replacable.

Sky Campbell 11-08-2019 10:37 PM

Itís a shame you donít share your formulas. You obviously did in the past but why is it such a secret now? Itís a clear glass base that took many years to develop I understand that. I respect the intellectual property but canít understand why you critique and say that is a old formula or that wonít work and expect everyone to make the same mistakes you did. Arenít we here to push what we do forward? I find some glass people to be an open book and share the passion others. Then we have another group that is guarded and fear they will lose power or money if they share. I mean no disrespect but getting actual working formulas from you seems harder and harder as time goes on. You have everyoneís respect in the community but if your not going to publish your findings for cash why not share?

Paul Stout 11-09-2019 12:15 AM

Thank you, I see your point. I'm struggling right now as a beginner mixer because I don't really know how much of what is in the batch we buy. I know the ingredients but not the amounts. Though I've blown glass for over 20 years I've never mixed my own clear from scratch and in fact have only been melting batch at all for two years (since the cullet crises). The issue is further complicated by the fact that there are no expansion values for colorants so knowing how to adjust a clear base to compensate for the colorants seems almost impossible without a lot of guessing and trial and error ( I realize there's a lot of trial and error even with the values, but at least they help one get started). Which Im happy to do but Im also running a public access hot shop and making my own work, so time to experiment is not as forthcoming as I would like. So I guess my first task is coming up with a formula for clear that would fit East Bay and have known quantities so that making adjustments to it gets a lot easier. So that's why I'm looking for clear recipes as starting points. I saw yours and thought it had most of what I was after in that it was a 96, had potassium, and no nitrates. Not having a better place to start I thought I would start there. I posted it because there's a lot I'm ignorant of and I'd like to learn and draw on the communities experience as much as possible. But I can accept that often the answer is "try it and find out".

Pete VanderLaan 11-09-2019 10:59 AM

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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