Arts and Entertainment > Ceramic and Pottery Defects 9: Defects Generated During Gelding Operations
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Article rating : 0.00, 0 votes. Author : John T Jones, Ph.D.
You are technically helpless in some ways when it comes to gelding. You are at the mercy of your gold supplier. Preparations of gold emulsions used in ceramic decorating are prepared in secret. Any technical problems relating to the emulsions used must be resolved by the gold vender. Also, the emulsion suppliers often adjust emulsions to resolve problems not caused by regularly used emulsion formulations.
Gold and other precious metal emulsions are used in the ceramic industry to add value to a product. This is usually in the form of banding or hand painting. Banding can be by hand or by machine. On firing, the gold must sink to the proper extent. It is called soft if it easily abrades off with a pencil eraser. If it sinks too far into the glaze and looses its ability to be buffed to a fine polish, it is called hard.
Hard gold can be caused by soft glaze. That is the glaze is more fusible than usual. The decorating supervisor tells the lab that the glaze is soft, lowers his decorating kiln temperature, and hopes the next lot of glazed ware will not cause him more problems.
Soft gold from hard glaze causes him to raise his decorating kiln temperature. This may cause blistering of the gold or other problems. The gold emulsion supplier can make the emulsion more suitable for higher firing.
So the problem is glaze control.
Why do you have variation in the hardness of the glaze?
Remember that we are talking about fusibility here.
Most fine china glazes are lead based. Lead bisilicate is a lead frit commonly used. It is make in large batches and the specific gravity of each batch is different. Therefore the laboratory at the factory must calculate the lead content of a glaze made with a particular frit batch. If the lead content is too high, then the lead bisilicate must be cut back. If the calculated lead content is too low, it must be increased.
The best control for the glaze itself is the FIRED specific gravity. Fire a cup of glaze, break out a chunk, and measure the specific gravity. Use this as a control procedure.
To maintain better control, blend frit batches before glaze formulation to even out the composition. Work with your suppliers to standardize their materials. Blend glaze batches to get the right glaze hardness.
Well, that’s about what I know about this business.
I hope you have enjoyed this series.
Say, “Hello!”
John T. Jones, Ph.D. (tjbooks@hotmail.com, a retired VP of R&D for Lenox China, is author of detective & western novels, nonfiction (business, scientific, engineering, humor), poetry, etc. Former editor of Ceramic Industry Magazine, Jones is Executive Representative of International Wealth Success. He calls himself "Taylor Jones, the hack writer."
More info: http://www.tjbooks.com
Business web site: http://www.bookfindhelp.com (IWS wealth-success books and kits and business newsletters / TopFlight flagpoles)
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