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cone 6 glaze test results-floating blue

updated tue 30 apr 96 on tue 23 apr 96

Hi all,

I noticed that the Floating Blue has popped up again. It is a glaze I'm
familiar with since I've been using it for about 3 years. What caught my
eye, was the description of it as "slate blue", which doesn't fit my results.
So, I picked up the original recipe, and it differs from the one Sharon
posted. If you're interested, you might try this version in your tests. It
is called Floating Blue...from James Chappell's book, Clay and Glazes.

Floating Blue Glaze Cone 6

Neph Sy...............47.3
Gerstley borate......27.0
Silica................... 20.3
Kaolin (EPK)........ 5.4
Red Iron Ox......... 2.0
Cobalt Oxide....... 1.0 (I substitute Cobalt Carb 2.0)
Rutile (milled)...... 4.0
C.M.C. ............. 1.0

This glaze produces a deep blue-brown background of great depth with lighter
mottled blues that seem to float on the surface of the background glaze.

The glaze has more of the lighter mottled blues where the application is
Watch thickness near the bottom of the pot.

The C.M.C. measurement refers to a premixed CMC and water solution. For the
Silica, I use 325 mesh Flint. The rutile, is just powdered rutile from the
ceramics supply. It fires best on the light side of cone 6 (standard cone
just bending), seems to get greener and more fluid the higher you go. Cone 5
works well, too. I do not find a need for bentonite.

The book says to weigh the ingredients very carefully, use distilled water or
water that is known to have a low mineral content. Mix then add the CMC
solution. Sieve two or three times through a 60 to 80 mesh sieve to
thoroughly disperse the cobalt, iron, and rutile.

The book warns that the glaze is fickle, and recommends against firing this
glaze in the same kiln with glazes that contain copper, chrome, nickel or
manganese. Mineral content of the water is an important factor. I have
noticed an adverse effect as the author noted, and now fire an entire kiln
load of this glaze.

The glaze should be stirred occasionally during application because the iron
has a tendency to settle.

Chappell's Suggested variations: Stipple on additional glaze with brush or
apply with sponge for an even more mottled effect. Or: lightly sponge a
thin wash of 3 grams of chrome oxide to 100 grams of water plus a tablespoon
of CMC over the top to produce a floating blue glaze with subtle green tints.
Or: Over the glaze, sponge lightly with a rutile wash consisting of 2 grams
rutile per 100g of water for a floating blue glaze with slightly tan
crystalline tints on the surface.

With leg propped up, recovering from knee surgery and wishing I were in the

Candice Roeder
under gray Michigan skies