mel jacobson on mon 1 may 00
a question please:
would a cover glaze, clear, high silica be a good
alternative over a highly oxided glaze? esp when
used for food.
for years i have used a final coat of rhodes 32 base over
my colored (blue) glazes. also, i have never liked the
look of oxides on the surface of glazes, therefore i have
chosen to always use a thin cover glaze....such as:
celedon one dip, oxide design, then a final coat of celedon.
it seems that oxides become more beautiful when coated
with clear.
it is like painting a car with clear coat after the color coat.
gives the color depth.
does this translate into ceramics? and help reduce leaching?
just a thought.
mel/mn
minnetonka, minnesota, u.s.a
http://www.pclink.com/melpots (website)
John Hesselberth on tue 2 may 00
Hi Mel,
Perhaps..maybe even probably. I have successfully used a stable, clear,
thin overcoat glaze over a copper containing glaze that leached fairly
badly. Cut the leaching by a factor of about 10. In another experiment
I cut it by a factor of 5-6. So it is a concept that is worth pursuing.
I expect the effectiveness may be dependent on how long you soak at
temperature or near temperature and how thick your overcoat glaze layer
is (mine were about as thin as they could be). The longer you give for
the two glazes to intermingle, the less effective it may be. I have too
little data to say it will work every time, but it is certainly worth
testing and it will help some. John
mel jacobson wrote:
>----------------------------Original message----------------------------
>a question please:
>
>would a cover glaze, clear, high silica be a good
>alternative over a highly oxided glaze? esp when
>used for food.
>
>for years i have used a final coat of rhodes 32 base over
>my colored (blue) glazes. also, i have never liked the
>look of oxides on the surface of glazes, therefore i have
>chosen to always use a thin cover glaze....such as:
>
>celedon one dip, oxide design, then a final coat of celedon.
>
>it seems that oxides become more beautiful when coated
>with clear.
>
>it is like painting a car with clear coat after the color coat.
>gives the color depth.
>
>does this translate into ceramics? and help reduce leaching?
>just a thought.
>mel/mn
>
>
>minnetonka, minnesota, u.s.a
>http://www.pclink.com/melpots (website)
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"Pots, like other forms of art, are human expressions: pleasure, pain or
indifference before them depends upon their natures, and their natures
are inevitably projections of the minds of their creators." Bernard
Leach, A Potter's Book.
Tom Buck on thu 4 may 00
mel:
You ask if a clear glaze over a coloured glaze would enhance the
food-safety, given that the clear glaze was balanced and suitable for the
claybody and the clear itself had no components that would be harmful if
in contact with acidic/akaline foods.
I guess you suspect the coloured glaze may not be kosher, and that
the covering clear would render it "safe".
Let's quote the well known phrase: "It depends". Ideally, when a
pot receives a 2nd coat of a different glaze, the amount of interaction
between the two glazes will largely be a function of their individual
makeup and the relative thickness of the two coats.
If the two glazes are "in the ballpark", ie, well designed for the
firing regimen, C6, C10, whatever, then assuming the two coats are
approximately the same thickness, the molten glazes will diffuse one into
the other, and in effect you will have one glaze; the colourant percentage
will be halved, and that of course could make it closer to food-safe, in
fact, the resultant solidified glaze may be fully food-safe.
But what about non-ideal situations? Hard to predict but it may be
possible to have two immiscible glasses form, one next to the pot
(coloured), and one on the surface. With almost zero interaction between
the two layers, then the properties of the clear base would dominate the
pot's surface. This condition would achieve what you hoped for.
Others may supply recipes for such immiscible glazes.
Til later. Peace. Tom B.
Tom Buck ) tel: 905-389-2339 (westend Lake Ontario,
province of Ontario, Canada). mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
Ray Aldridge on fri 5 may 00
At 02:12 PM 5/4/00 EDT, you wrote:
>----------------------------Original message----------------------------
>mel:
> You ask if a clear glaze over a coloured glaze would enhance the
>food-safety, given that the clear glaze was balanced and suitable for the
>claybody and the clear itself had no components that would be harmful if
>in contact with acidic/akaline foods.
(snip)
> But what about non-ideal situations? Hard to predict but it may be
>possible to have two immiscible glasses form, one next to the pot
>(coloured), and one on the surface. With almost zero interaction between
>the two layers, then the properties of the clear base would dominate the
>pot's surface. This condition would achieve what you hoped for.
Another possible approach to using iffy glaze colorants safely might be to
use them to color a fairly refractory slip, and then use a well-balanced
but not particularly active clear glaze over the slip.
Ray
Aldridge Porcelain and Stoneware
http://www.goodpots.com
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