Carole Fox on tue 29 may 01
Hi clayart friends,
Seems like there isn't much to worry about electric firing iron-bearing =
clay. Most people responding to my query insisted that their experience =
shows that it does not harm the kiln.
Tom Buck said-
". Iron compounds usually do not
become voltile...excepting iron sulfide or sulfate, both natural =
minerals,
and it would be the SO2 coming from them that would attack the =
elements.
But prepared mid-fired highfire claybodies do not contain any amount =
of
sulfides or sulfates. Raw terracottas might.
[and]
if the electric kiln is properly vented (as it should
be in a teaching studio), then damage to the elements from the SO2 =
will be
very low, less than that caused by boiling off metal from the
Iron/Aluminum alloy of the elements"
Ivor Lewis said-
"There is no doubt that many clays can give of sulphur trioxide and =
sulphur dioxide during firings, but these could come from other sources =
such as Anhydrite or Gypsum.
Your Professor friend is correct. It is a fact that some types of =
natural stoneware clay contain sulphur combined with iron in the form of =
Iron Pyrites. This can be determined by taking some of the clay and =
washing it in a gold pan to get rid of the light clay fractions. If Iron =
Pyrites is a natural ingredient, it will be visible as golden flecks =
either with your naked eye or a X10 hand lens.
However, I have never read of sulphur gases causing corrosion of =
Nichrome or Kanthal elements. A health hazard, yes in a place where =
ventilation is restricted"
But perhaps Kurt Wild said it best when I asked if this claim of kiln =
damage was for real when he said-
"Baloney!"
Thanks to all who responded,
Carole Fox
Elkton, MD
cfox@dca.net
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