Soluble Salts

Metals give color in ceramics and glass. Each metal has several chemical forms, but with few exceptions, industry and almost all studio potters use either the oxide or carbonate forms because they are stable, predictable, relatively inexpensive, thoroughly researched, and not water soluble.

The nitrate, chloride, and sulfate forms of metals (metal salts) are water soluble, and although much less researched, and more challenging to control and use, they offer artistic effects that are impossible to achieve with their tamer cousins.

	Some can form haloes when applied over other solubles, and mixtures of solubles sometimes form two, and even three color haloes (left). Some will produce a color with soft, diffuse edges (right), others leave a crisp edge.
	Phosphoric acid will displace the color it is brushed over, leaving a colorless center and a dark edge at the boundary of the brush mark (left). Colors mixed in mild acidic or basic solutions can react with each other, leaving fumed or smoky haloes (right).
	Soluble colors are transparent because there is no pigment in the solution, and two colors can be layered over each other to create a third color if a piece is bisque fired between applications of each soluble (called "setting" a color).

Also, solubles will change color slightly depending on what temperature they are fired to, and they can be applied at either the slightly damp greenware, bone dry greenware, or bisque stage, some giving slightly different effects at each stage. They can be used as fuming agents in saggar and vapor firings, and they can color terra sigillata without dulling or matting the surfaces as oxides do. Add to this the fact that there are more than fifteen metals that give useful colors, and you find that solubles are capable of color nuances, effects, and interactions that are unique in ceramics.

I think that solubles intrigued me partly because I came of age in San Francisco, CA, in the late 1950's — a time of experimentation and fluid boundaries — so when I began working as a studio potter in the mid 70's, it seemed natural for me to try water-soluble chlorides of iron, copper, and cobalt, simply out of curiosity. But it was only after reading Arne Åse's book, "Watercolour on Porcelain" in 1988 that I became aware of the much larger range of colors and effects that various water-soluble metals offered. I've continued testing and experimenting over the years whenever a busy work schedule allowed, gradually accumulating both a fluency of use and a greater appreciation of potential effects — they integrate nicely with my influences from calligraphy, Asian ceramics, and painting/printmaking. I've also gradually incorporated elements from my woodfiring experiences and my extensive use of stained crackle glazes into my soluble work, so that now I'm sometimes 'painting' with glazes and ash, as well as soluble colorants. The pieces are certainly abstract rather than representational, but several have a feel to me of deep space, and galaxies of stars...

I've also gradually incorporated elements from my woodfiring experiences, and my extensive use of stained crackle glazes into the soluble pieces, so that now I am sometimes "painting" with glazes and ash, as well as colorants. The pieces are certainly abstract rather than representational, but several have a feel to me of deep space, and galaxies of stars. To the right: Eta and Keyhole in the Carina Nebula
(© Brad Moore). Click the image for an enlarged view.

I gave a presentation on water-soluble metals at the 2004 NCECA conference, and I intend to write occasional articles for various ceramic publications as my investigations continue.

Click on the thumbnails for detailed views.