Joseph Herbert on sat 9 aug 97
Adding to Bill Aycock s comments about Lead Glazes, We aren t used to
materials that change from solid to gas and back to solid. Crystalline
iodine is the usual demonstration material in high school chemistry. A metal
that vaporizes in a hot area, like the kiln, solidifies as soon as it gets to
a cool enough surface. Cool may not be all that cool. If the metal deposits
on surfaces cooler than 1500 degrees, for example, it would build up on the
outer half of the bricks along the top edge of an electric kiln. All the
dust particles on that part of the kiln would become covered with lead and
then stick to your hands and clothing. Nice.
Another example of this is arsenic in coal. Arsenic is vaporizes as the coal
burns but deposits on surfaces cooler than about 1540 degrees. This means
that most of the arsenic that is brought into a furnace stays there. The
amount per pound of coal is small but it all stays and huge amounts of coal
go through a power plant furnace. The result is the coating of most of the
interior surfaces of the furnace with arsenic. Causes problems for the
people who have to go in there from time to time.
Anyway, the characteristics of materials that do that solid-gas-solid thing
are Tricky and Unfamiliar. Extra care is required, avoidance is recommended.
Joseph Herbert
JJHerb@alo.com
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