Michele Jurist on fri 26 mar 99
Hi everyone:
I recently read that the scumming that occurs on pots with some alkaline
glazes is the result of overfiring and can be removed with a mixture of
vinegar and salt. My ceramics teacher disputes this to be true, saying the
scumming has appeared on pots that she fired for only 6 hours.
Does anyone know why the scumming occurs? Is it the glaze or the firing or
both? Is there a solution? Thank you in advance to anyone who replies.
Michele
John K Dellow on sun 28 mar 99
Michele Jurist wrote:
>
> ----------------------------Original message----------------------------
> Hi everyone:
>
> I recently read that the scumming that occurs on pots with some alkaline
> glazes is the result of overfiring and can be removed with a mixture of
> vinegar and salt. My ceramics teacher disputes this to be true, saying the
> scumming has appeared on pots that she fired for only 6 hours.
>
> Does anyone know why the scumming occurs? Is it the glaze or the firing or
> both? Is there a solution? Thank you in advance to anyone who replies.
>
>
Michele , if you are referring to terracotta pots , then sometimes the
clay has small amounts of soluble salts in it ,either present in the
clay or from the water used to make the clay body. Also
the water used to work with the body may have these salts present .
Alternatively a pot will scum after being filled with soil , which may
have soluble salts in it or the water used to water the plane has
soluble salts in it .
I have posted that "Canola " oil rubbed onto the pot will remove
the scumming , and have confirmation from a calyarter as to it working.
As to glazed earthenware or other clays I have no knowledge.
--
John Dellow "the flower pot man"
ICQ : #2193986 {jacka}
E-mail : dellow@usa.net
25 Hugh Guinea Ct, Worongary Q 4213
Ph:+61-7-55302875 Fax:+61-7-55253585
Home Page http://www.welcome.to/jkdellow
Pancioli on mon 29 mar 99
Hi Michelle:
I have seen a high alkaline glaze like Gill Blue break down--a white
powdery substance appears on the surface. Hi alkaline glazes are known
to be unstable. I don't think it is the same as body scumming, which
as I understand it, is caused by dissolved materials (soluble salts) in
the clay. When the water evaporates, the dissolved material is
deposited on the surface--sometimes forming a thin hard crust that
makes the pot hard to glaze. There is a good section on scumming in
Hamer's book.
Diana
Sharon Pollock-De Luzio on thu 1 apr 99
I'd like to add to, and hopefully not confuse the question of this issue. I
have recently had glazes leave spots that looked like scumming, but the
whitish areas don't respond to any attempts at removal. Someone mentioned
"devitrification".
Any thoughts anyone?
Sharon in RI
Michele Jurist wrote:
> ----------------------------Original message----------------------------
> Hi everyone:
>
> I recently read that the scumming that occurs on pots with some alkaline
> glazes is the result of overfiring and can be removed with a mixture of
> vinegar and salt. My ceramics teacher disputes this to be true, saying the
> scumming has appeared on pots that she fired for only 6 hours.
>
> Does anyone know why the scumming occurs? Is it the glaze or the firing or
> both? Is there a solution? Thank you in advance to anyone who replies.
>
> Michele
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