momsmith on wed 31 may 00
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"Morris, Marlene F." wrote:
> > but I'm still wondering what it is
> > about reduction that does damage to the elements. Can someone enlighten
> me? Whatever
> > it is I can imagine that the effect would be much more pronounced at 1200
> than at
> > 500.
> > Thanks again,
> > Reid Harvey
> > Ceramiques d'Afrique
>
> Hi there,
>
> I'm very new to firing, just on the point of buying a kiln, so I wanted to
> ask about this, too.
> I just read this in Harry Fraser's book "The Electric Kiln" (1994):
>
> "An important feature of Kanthal wire is that after firing, the wire builds
> up a layer of aluminium oxide on its surface which protects the wire from
> attack by harmful furnace gases. It takes two or three firings for this
> protective layer to form and for this reason the initial firings of a new
> kiln or one fitted with new elements should be test or biscuit firings
> rather than glaze ones due to the much more corrosive nature of the gases
> liberated in glaze firings. Also, exposure to reducing atmosphere will
> remove the protective coating and the elements will then rapidly deteriorate
> unless the coating is restored by an oxidising fire. This is why reduction
> firings in an electric kiln should always be followed by at least one
> 'clean' oxidising fire. Even so, it must be repeated that reduction firings
> significantly reduce element life."
>
> Each book I'm looking at warns against reducing in an electric kiln, giving
> the shortened element life as the reason.
>
> If I wanted to reduce in a saggar in an electric kiln, would that also be a
> problem?
>
> But I wouldn't throw sawdust into the thing -- I value my skin too much for
> that.
>
> Marlene
>
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