Marni Turkel on sat 30 aug 97
If there are soluble ingredients in the glaze (intentionally or not) they
can show up as a discolored area on the ware as is dries. Forced air speeds
up the drying and causes it to concentrate on a particular area where water
is evaporating the fastest. If someone touches the piece and leaves an oily
hand or fingerprint, the oil will work as a resist, blocking the
evaporation at that point and, consequently, blocking the deposit of the
soluble material. If the soluble material is an active part of the glaze,
it will be evident after the firing.
Marni Turkel
Stony Point Ceramic Design
Santa Rosa, California
Erin Hayes wrote:
>While I was working on my class guide for fall term, I came across the
>section on scumming and remembered a question I wanted to put to
>everyone (the answer to which my students invariably want and I can't
>provide them for certain) -
>
>Have you ever seen a yellowish stain develop on a freshly glazed piece
>as it dries?
>
>We sometimes see a light yellow cast come up on frshly glazed work in
>the studio. Usually it is when the A/C is on, sometimes it is shaped
>like handprints and sometimes not. Sometimes it will persist after the
>Cone 10 firing if it has appeared on a white or clear glaze, so it must
>be inorganic.
>
>I keep thinking this must be a different sort of scumming than I've seen
>in clay bodies, but I wanted to know what all-uh-y'all think.
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