Don Goodrich on tue 7 dec 99
Hi Tasha,
There've been a few variations of FB posted on Clayart over the years,
including a fritted one from Ron Roy that I have yet to try. The one I use is
directly from Chappell, with the addition of bentonite, and substitution of
cobalt carbonate for the oxide:
Floating Blue ^6 oxidation
47.3 Nepheline Syenite
27.0 Gerstley Borate
20.3 Silica Flint
5.4 EPK
2.0 Red Iron Oxide
1.0 Cobalt Carbonate
2.0 Bentonite
1 teaspoon CMC
I also make a point of using distilled water, letting the glaze settle a few
days and pouring off excess water from the top. This probably reduces the
boron content somewhat. I occasionally add epsom salts to a batch, stirring
in a pinch at a time, until it thickens noticeably and adheres to smooth
objects dipped into it.
One of Tony Hansen's many informative web pages
explained (I think) why my initial batches were such disasters. Since boron
is soluble, it can be sucked into the dry bisque and form a more
highly-fluxed layer at the clay/glaze interface. When fired, this more fluid
layer would make the glaze flow off the pot, as mine did. Tony also suggested
bisquing to ^04 so the clay absorbs less of that fluxed water.
I'm not sure which of these bits of tinkering helped the most. Thickening
the glaze allows me to get the right thickness with only one dip. Using
distilled water eliminates unknown minerals from my hard tapwater. Bisquing
higher helps keep the soluble flux in the glaze. Bentonite (and CMC) seem to
make it stickier.
This is not a glaze I'd recommend firing before it and the pot it's on
have dried. If dried too fast, it can crack and peel right off a pot, leaving
flakes waiting to melt on your kiln shelves . This problem can also be
avoided by applying it to almost-bone dry greenware which is then allowed to
dry fully.
Although Chappell says to apply to the thickness of a dime, I've found
that to be excessive and to invite crawling. It does have to be relatively
thick, or you get the famous uninvited green/brown color variation. The body
it's used on makes a color difference. I work with Great Lakes Superior
Stoneware, a light buff body, and get a brighter blue than one would on a
higher iron or manganese clay.
Sorry to carry on so. You didn't say which of FB's problems you'd
experienced and there are several variables besides the recipe, so I tried to
cover all I could think of.
Hope this helps,
Don Goodrich in snow-covered Zion, Illinois
goodrichdn@aol.com
http://members.aol.com/goodrichdn/
Tasha Olive said:
>>... if you would be
so gracious as to post your recipe of Chappell's Floating Blue. I have a
recipe for a floating blue and have never gotten good results AT ALL...<<
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