[Natania Hume]

I keep seeing the description "nuka glaze" on pieces I admire - a creamy white high fire glaze. Is nuka a kind of ash? I'd love to find a mid range recipe for this type of glaze but it probably doesn't exist...

[TJR]

It's a soft, white-grey semi matt glaze. It does contain wood ash. I will post a recipe when I get to the studio.
John Baymore would be able to tell us more about it.
TJR.

[JBaymore]

Writing from NCECA.....working totally from memory here.... my glaze file is not here.

"Nuka" is the Japanese word for the husk (or hull) of the rice kernel. It is a by-product of the milling of white rice. The Japanese version is from a short grain rice.

Potter parlance (in Japanese) uses this term for glazes based upon rice HUSK ash (not rice straw ash....... different chemical composition). The agricultural waste is piled in the fields and is then burned. The piles smolder more than burn, and a good ash for glaze use is actually dark grey to black. You don't want it to burn cleanly. This color comes from carbon residue in the ash. SO the ash has a high L.O.I. The chemical composition of rice husk ash (after L.O.I.) is almost colloidally fine silica. (TJR I'd call it more of a semi-gloss.)

Nuka glazes are high calcium fluxed glazes (from the washed wood ash) what use the rice husk ash for a lot of the silica content, and bringing in the silica in a very fine particle size. They fire a bluish white and are slightly milky opaque where thicker due to the unmelted silica particles.

I use real rice husk ash (imported and expensive) and washed hardwood ash. Firing it from Orton cone 10 to Orton cone 14. The recipe I started with I got from Hamada Shoji-sensei.

1/3 rice husk ash
1/3 wood ash
1/3 terayama stone ( a high silica bearing feldspathoid)


That is modified for more locally available materials as...............


32% rice husk ash

32% wood ash

32% Custer feldspar

4% flint

This stuff is natural material glaze.... the slurry handles VERY differently from what most people are used to when ucing commercial beneficiated materials. It looks REALLY thick when on the proper consistency, and is sort of "fuzzy" looking. It setles down in firing due to the high L.O.I. of the rice husk ash.

Hope this is of use.


best,

...................john

[Natania Hume]

JBaymore, on 20 March 2013 - 10:50 PM, said:

Writing from NCECA.....working totally from memory here.... my glaze file is not here.

"Nuka" is the Japanese word for the husk (or hull) of the rice kernel. It is a by-product of the milling of white rice. The Japanese version is from a short grain rice.

Potter parlance (in Japanese) uses this term for glazes based upon rice HUSK ash (not rice straw ash....... different chemical composition). The agricultural waste is piled in the fields and is then burned. The piles smolder more than burn, and a good ash for glaze use is actually dark grey to black. You don't want it to burn cleanly. This color comes from carbon residue in the ash. SO the ash has a high L.O.I. The chemical composition of rice husk ash (after L.O.I.) is almost colloidally fine silica. (TJR I'd call it more of a semi-gloss.)

Nuka glazes are high calcium fluxed glazes (from the washed wood ash) what use the rice husk ash for a lot of the silica content, and bringing in the silica in a very fine particle size. They fire a bluish white and are slightly milky opaque where thicker due to the unmelted silica particles.

I use real rice husk ash (imported and expensive) and washed hardwood ash. Firing it from Orton cone 10 to Orton cone 14. The recipe I started with I got from Hamada Shoji-sensei.

1/3 rice husk ash
1/3 wood ash
1/3 terayama stone ( a high silica bearing feldspathoid)


That is modified for more locally available materials as...............


32% rice husk ash

32% wood ash

32% Custer feldspar

4% flint

This stuff is natural material glaze.... the slurry handles VERY differently from what most people are used to when ucing commercial beneficiated materials. It looks REALLY thick when on the proper consistency, and is sort of "fuzzy" looking. It setles down in firing due to the high L.O.I. of the rice husk ash.

Hope this is of use.


best,

...................john

Thank you very much. Extremely informative. What is L.O.I.?

[JBaymore]

Loss On Ignition. It is the difference in molecular weight when the material has been heated up to reactive temperature / oxidized in the kiln and the starting molecular weight In this case carbonaceous matter gets turned to CO₂ and things like carbonates give up the CO₂.

best,

....................john