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bristol glaze, was re: mocha slip

updated tue 18 jan 05

 

Kate Johnson on mon 17 jan 05


Hi Russel and list...
>
> >> So...there appears to be a bit of a trick in glazing, after you've
> bisque fired the pots. Zamek says you can dip, pour, spray or brush the
> glaze on...but others have had problems losing the dendritic aspect of the
> design. He doesn't mention any problems in this process, nor have any of
> the books or articles I've looked at. <<
>
> I think this technique was originally developed with a very stiff glaze
> called a "Bristol Glaze". In any case, I think you need to use a glaze
> that
> will not move very much and won't "eat up" the finer details of your
> design.

I've been googling Bristol glaze and have found a lot of mentions...looks
good. So far haven't found a recipe, other than an old Clayart mention that
the potter had used a white zinc-based Bristol. That would opacify it,
would it not? I need a clear glaze, and the samples of antique pots I've
also looked at obviously had that.

Recipes, anyone?

Best--
Kate

Rick Hamelin on mon 17 jan 05


Hi Kate
Bristol Glaze historically used zinc oxide as a substitute for lead. It is a mid-range temperature glaze..cone 1 and you find it on the kitchen stonewares replacing salt glaze. It was a white glaze and I have never found it mentioned as the glaze for mochaware. Zinc is used in varying amounts in glazes above (from memory) 2000F'. It can ruin (muddy) many colorants.
Historical mochaware was a lead glaze, I suspect a fritted lead and borate combination in England. Don Carpentier produces a high quality product.
http://daats.com/gac/aboutdon/aboutdon01.htm
http://daats.com/gac/articles/pottery.htm
"Don quickly brushes some glaze color onto the rouletted bands. On firing, this will turn a bight translucent green, related to the green shell edge coloring so prevalent on pearlware plates and platters of the same period. Don has struggled to get the right green. On period examples an oxide of copper was used which reacted in the kiln to the lead in the glaze to produce a brilliant green that seems nearly impossible to achieve any other way. He's don some limited trials using lead to prove his point but will only produce wares with lead-free glaze. Through trail and error, he's arrived at a successful an sale approximately"

Rick

--
"Many a wiser men than I hath
gone to pot." 1649

-------------- Original message --------------

> Hi Russel and list...
> >
> > >> So...there appears to be a bit of a trick in glazing, after you've
> > bisque fired the pots. Zamek says you can dip, pour, spray or brush the
> > glaze on...but others have had problems losing the dendritic aspect of the
> > design. He doesn't mention any problems in this process, nor have any of
> > the books or articles I've looked at. <<
> >
> > I think this technique was originally developed with a very stiff glaze
> > called a "Bristol Glaze". In any case, I think you need to use a glaze
> > that
> > will not move very much and won't "eat up" the finer details of your
> > design.
>
> I've been googling Bristol glaze and have found a lot of mentions...looks
> good. So far haven't found a recipe, other than an old Clayart mention that
> the potter had used a white zinc-based Bristol. That would opacify it,
> would it not? I need a clear glaze, and the samples of antique pots I've
> also looked at obviously had that.
>
> Recipes, anyone?
>
> Best--
> Kate
>
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