OK, so I scored BIG today!  I was at one of my not so local suppliers & they let me go back & look on their shelves, 'cause I had been asking about lead products and I was able to snag 18 lbs. of lead bi-silicate & 15 lbs. of red lead oxide.  I know, I know!  I wear gloves & a respirator when I mix & spray and I don't make anything utilitarian.  I only use this stuff in crystalline glazes and am very careful to keep it high up & put away.  In fact, I think I will go buy a couple of heavy duty containers to put it in for a little extra protection. jhp

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Comment by Norm Stuart on December 29, 2013 at 10:33pm

I have no idea how much of a vaporized metal oxide escapes condensation on a surface to become dispersed in the air.

All metal oxides vaporize increasingly, at different temperatures, as the temperature rises.  We don't have a down-vent so you can clearly see a lot of metal oxide deposits condensed on the Monel stainless kiln jacket over an area three inches above the top peephole, and on the Monel cladding all around the lid.

If you have a down-vent, that's where a lot of it goes, condensed inside the exhaust pipe.

Chrome vaporization is responsible for traditional Red chrome-tin glazes going white where they're too hot for too long.

A year ago or so online I actually found a very old ceramic industry table of lead vaporization, as a percentage loss per hour, at various temperatures. As you said, as the firing temperature rises, the percentage of lead lost to vaporization each hour increases.  From memory I think the percentage loss per hour was fairly low, about 1.5% per hour, until Cone 03. Which probably explains why lead works so well in metallic gold looking glazes at cone 04 to cone 06 - like Clay Planet's "Aztec Gold". http://shop.clay-planet.com/pint-722-aztec-gold.aspx

Lead melts at 328 C and boils at 1,749 C. So as the temperature moves up from 328 C you lose lead to vaporization at a faster and faster rate.

Queenstown, Tasmania Australia was once fully forested in Huon pines. But it hosted several copper smelting plants on Mount Lyell.   Due to a combination of tree removal for use in the smelters, the smelter fumes (for about 40 years), and the heavy annual rainfall, the erosion of the shallow horizon topsoil back to the harder rock profile contributed to the stark state of the mountains today.

Today the copper ore is still mined, but smelted in Tuticorin India - which is probably a Hindi name for "city which can't be seen from Australia".

Huon pine forest:


Queenstown today:

Queenstown Tasmania smelters at their peak:

Queenstown in 1984 just prior to closure of the smelters:


Comment by George Lewter on December 29, 2013 at 9:38pm

You know the lead will vaporize off more and more as you rise above low fire temperatures, right? Then it condenses and lead dust coats whatever it lands on downwind of its source. Is this essentially correct, Norm?


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