Martz Memories, by
Getting Lead Out Pottery That Teaches Tale #15
One would think that with such a large collection of his own works to call upon. Karl Martz would have little purpose to use another potter’s work for illustration. As students, we always liked to see pots our master had produced, whether past or present. To view his pottery close up encouraged us to improve our own skills. He would show his pleasure when we showed progress, and that encouraged us all the more.
On our last visit to Karl and Becky Martz, we talked about
the crystalline glazes Karl had exhibited at a faculty pottery display. When there was a lull in the conversation, he
suddenly said, “I broke your beaker,
“Yes. The one with the A.F. glaze on it.”
For years, and unknown to me, he had been showing my simple shape to his classes so they could see the delightful effects from variations of the A.F. glaze. The original glaze fired to cone six, but when we worked with it, we saw the formula had to be changed, for it called for ten per-cent of raw white lead. Ceramics teachers were concerned for the health of everyone who used raw lead in glazes. Not only was it easy to ingest small amounts of lead while mixing ingredients, but Lead vapors were released in the kiln atmosphere. In other cases, fired cookware glazes released small amounts of lead as they came in contact with acidic foods. Lead poisoning resulted. Karl Martz wrote articles to enlighten many of these health dangers.
Glaze manufacturers devised ways to avoid raw lead in glazes. By a process called fritting, they were able to combine lead with silicon, and so produce non-toxic lead-silicate. Silicates did not release lead in dangerous amounts as called for in glazes. Civilized man found other ways to ingest lead. Our problem was to find ways to get the lead out of our favorite A.F. glaze formula, especially if we did not wish to use silicates.
…..There were fluxes other than lead we could use. Whiting was one, and Zinc oxide was another. We used them to replace the lead in 1974, and in 1984, my A.F. modifications still used them to replace lead. We got the lead out of our glazes. Uninformed potters did not see the need, and some of the dangers of lead ingestion remained hidden.
We should remember, before the kiln reached earthenware temperatures, some of the raw lead volatized, and these poisonous fumes went into the air and could be breathed by any unsuspecting person. Country potters who had outdoor kilns did not seem to be concerned. The lead melted quickly and assisted the other glaze ingredients to flow and meld. The result on earthenware appeared as a smooth shiny surface, and this helped to sell the finished product.
In June 1976, Ceramics Monthly published my article, “A Portuguese Marketplace.” One photograph shows row upon row of “Brightly gazed earthenware platters, baking dishes, and other functional pieces .” For the time being, lead had served its purpose. We who know may still wish to follow Karl’s example and continue to enlighten others.
Thank you, Karl.