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Old 03-05-2006, 08:36 PM
Dave Bross Dave Bross is offline
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Pete liked the concept of me having all the answers!!!!!!!

Actually, Pete was the one who taught me all the basics and he knows a hell of a lot more than I do.

NO ONE has all the answers 'cause we still haven't even found all the questions.

Back to the concept of oxygen in the glass.

The oxygen has to be chemically combined with the glass to affect the oxides you use for color. In glasses that want oxidation for color you add more oxygen.

The oxygen has to be cut way back in colors that want reduction.

If you are going after a color that needs a greater amount of oxygen to go to the valance where it shows a particular color, it's best to get that oxygen in there via one of the chemicals going into the glass.

If you have a color that wants reduction, then you have to start with a glass formula that doesn't have any oxidisers, and also add reducing agents like some form of carbon or the black tin for copper ruby.

In the case of your cullet experiments you want to put in enough reducing agent to reduce the excess oxygen that is already there in the cullet.

The old timey way of making copper ruby was to re-melt and frit the cullet a number of times to reduce the oxygen in the glass.

The potassium tartrate your guy was adding is a reducing agent, but he probably didn't get enough in there.

Try sugar for reduction in cullet. The sugar becomes carbon when heated. Old time glass melters would chuck things like grain or coal into a glass to get reduction.

The potassium in the potassium tartrate is also moving the expansion of the glass higher and that's not going to help when you try to fit different glasses together.

The furnace atmosphere has a much smaller effect on the level of oxygen in the glass than chemical additions do. You can't ignore it though, it can change things enough to screw them up.

You can use the copper carbonate to replace the copper oxides in most things, you just have to do a little math to compensate because the carbonate has less percentage of copper in it. Here's a pretty good on line source for the percentages in materials:

http://ceramic-materials.com/cermat/material/a.html
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Last edited by Dave Bross; 03-05-2006 at 08:43 PM.
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