Berry Silverman on sun 21 dec 97
I am a brand-new participant, so please forgive any breach of etiquette
-- hopefully I can learn quickly. I am having a problem with black
underglaze applied on greenware, then dipped in clear leadfree glaze
before the second firing.
I make lowfire plates and bowls (^04 bisque, ^06 glaze) and use black
underglaze as a background color for the back of the plates/bowls, which
wraps around to the front to define a border. It has been difficult to
find a good match with the underglaze to get a real dark cobalt black
and still get a problem-free glaze coating.
The commercial underglazes I started with ended up coming out charcoal
grey, not black, with the leadfree glaze (also a commercial product).
When I finally found a good cobalt black that worked, my clear glaze
became temperamental. There is a very small tolerance between the glaze
being applied too thickly and becoming milky over the black and the
glaze being too thin, causing pinholes or glaze starved areas. It is
almost impossible to determine visually after dipping whether the glaze
is too thick -- excluding, of course, thick drips or glaze runback.
I can avoid these problems by thinning the underglaze with water until
it is very thin. But then the underglaze drips and runs on the front of
the plate where I am just using it as a border or outline for designs.
While I do make my living from my pottery, I am completely self-taught
and do not have an academic background in glaze composition -- just
learning by experience and trial and error. Any suggestions for taming
this problem are appreciated. Thanks for your thinking caps.
Berry in Tucson
Stephen Mills on tue 23 dec 97
Berry, I used to have the same problem with underglaze, particularly
when applied thickly to get a dense colour. Solved the problem by mixing
fritt or glaze powder (transparent) with the colour, it bonds with the
glaze coat and allows you to glaze thinly.
Steve
Bath
UK
Seasonal greetings to all especially our hard working moderators.
In message , Berry Silverman writes
>----------------------------Original message----------------------------
>I am a brand-new participant, so please forgive any breach of etiquette
>-- hopefully I can learn quickly. I am having a problem with black
>underglaze applied on greenware, then dipped in clear leadfree glaze
>before the second firing.
>
>I make lowfire plates and bowls (^04 bisque, ^06 glaze) and use black
>underglaze as a background color for the back of the plates/bowls, which
>wraps around to the front to define a border. It has been difficult to
>find a good match with the underglaze to get a real dark cobalt black
>and still get a problem-free glaze coating.
>
>The commercial underglazes I started with ended up coming out charcoal
>grey, not black, with the leadfree glaze (also a commercial product).
>When I finally found a good cobalt black that worked, my clear glaze
>became temperamental. There is a very small tolerance between the glaze
>being applied too thickly and becoming milky over the black and the
>glaze being too thin, causing pinholes or glaze starved areas. It is
>almost impossible to determine visually after dipping whether the glaze
>is too thick -- excluding, of course, thick drips or glaze runback.
>
>I can avoid these problems by thinning the underglaze with water until
>it is very thin. But then the underglaze drips and runs on the front of
>the plate where I am just using it as a border or outline for designs.
>
>While I do make my living from my pottery, I am completely self-taught
>and do not have an academic background in glaze composition -- just
>learning by experience and trial and error. Any suggestions for taming
>this problem are appreciated. Thanks for your thinking caps.
>
>Berry in Tucson
>
--
Steve Mills
Bath
UK
home tel: (44) (0)1225 311699
work tel: (44) (0)1225 337046
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