Snail Scott on sat 4 jul 09
On Jul 2, 2009, at 10:42 PM, Dana & Chris Trabka wrote:
> I reciently had a bowl glaze fired in a friend's electric kiln...When
> the bowl came out there were small dark abrasive flecks in the bottom
> of the bowl. Some of these flecks were covered by the glaze (a thin
> layer of a clear glaze) and some of the flecks were on top of the
> glaze. Those flecks were not seen any where else on the bowl. Has this
> happened to any one else? Any guess on what might be the cause?
The fact that all the bits were in the bottom
of the bowl indicates that the specks got there
while the glaze was sill unmelted, and fell to the
low spot of the bowl before the glaze got sticky.
The fact that some were imbedded in the glaze
and others were on top just means that some
sunk and were coated while others didn't sink
and were not.
Two ways this can happen: the piece had things
fall into it before it was loaded due to being kept
in a dusty environment, or the stuff fell in after
loading. If the piece was high in the kiln, the kiln
lid may have shed on the piece, though such
sheddings are usually tan, like the softbrick itself.
If the work was low in the kiln, stuff might have
fallen off the bottom of the shelf above (was it laid
on or against a dirty surface before loading?), or
brushed off of work that was loaded nearby
(same possibility - loose stuff picked up off the
surface the piece was sitting on earlier). I often
use a grinder near my kiln, and this leaves black
carbide or metal specks all over which could get
picked up on the work if I'm not careful and tidy.
Another possibility: If the kiln has an exposed
thermocouple, it may have spalled tiny bits of
itself (little dark bits) onto your piece if it was
nearby. These can spall if bumped when loading
as well as during firing.
-Snail
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