Technical archive

by Petra Svoboda

As a recent graduate student of the National Art School I found myself in good stead after three years of intensive study majoring in wood firing and the effect of ash glazes in this atmosphere. Beginning with the sourcing and digging up of my own clay, the processing of these materials constantly reinforces the relationship between maker and materials. Consequently the materials have a significant impact on the aesthetics of my work. The nature of the materials themselves establishes a dialogue between the glaze surface and body. There is also a sense of simplicity in design allowing the forms’ elliptical and distorted characters to protrude through the glazed surface. These peculiar and erratic marks leave a visible trace on the clay surface, reflecting the interaction between the clay and the fire. In no other process is this most pronounced as it is in wood firing; it promotes unpredictability formed from a natural progression from using found materials. The clay I use is an iron bearing stoneware from the Mittagong region in NSW. My principal glaze material is wood ash, which is used in conjunction with natural granites and feldspars.

The most intriguing aspect of glaze technology is the meeting of Art and Science. My initial interest in found materials led me to ASH. It somehow seemed natural to use a material that was just as unpredictable as the clay. It also appeared to be easy and inexpensive to obtain and most impor-tantly suited the texture and character of my work. The aim was to try to achieve some less conven-tional glaze qualities from the ash. I had always had an interest in Kuan glazes with their thick luscious texture and dark protruding clay body contributing to the depth of the glaze. They seemed to reinforce the aspect of maintaining a dialogue with the glaze and clay body that I was so interested in.

Potash Feldspar - 40 Substituting certain ingredients with ash or of Kaolin can produce interesting results
Silica -30
Whiting -20
Kaolin -10
Variations on
Potash Feldspar 70 70 60
Ash 20 30 30
Whiting 10 - 10


Talc (3MgO(4SiO2(H2O) was also introduced into the materials, because it has known qualities of opaqueness and matt ness. Talc in glazes provides unattached magnesium oxide and silica. It was used in a Leach Cone 8 recipe as a substitute for silica and in equal proportions with Potash Feldspar, Ash and Eckalite. It provided a thick creamy surface that was extremely sensitive to application and firing temperatures. The rich browns and reds from the body penetrated through the creamy glaze on the raised surfaces, the rims and indentations. Creamy and crackled where thick-brown and speckled where thin.

Wood ash has therefore become one of the most prominent materials in my glaze formulations. Ash is an ever-changing substance that creates varying and individual effects. Ivan Englund claims: “Ash is such an inconsistent material that it cannot be used in a glaze formula unless the batch is analysed and it has to be treated differently from most of the other glaze materials”. Ashes can vary enormously but are generally made up of 90% alkaline fluxes; the remainder is silica and phosphorus oxide. Thus it can easily be categorised as a natural glaze frit. Also, many ash glazes crystallise because they contain more than the eutectic amount of flux.

Ash can also be washed to remove the soluble alkalis. The minerals lost in washing are almost entirely potassium salts with some sodium - both valuable fluxes. I thus found it important not to remove the water in a glaze after it had settled because it contains many of the solubles.

This method of gathering materials and the whole woodfiring process has great historical connotations that are deeply entrenched in Oriental ceramic traditions. My work, however, moves beyond these concerns with the incorporation of screen printed decals having references to certain technological terms and diagrams that are relevant to my working processes, framing the work in a contemporary context. The ceramics that I make is very much about tradition-bound beliefs merging with contemporary thought. It was my intention then to create multi-narratives within my work as a deconstruction of ceramic/craft history by using these codes and references relating to traditional ceramic techniques. I also see it as a comment on the influx of Oriental aesthetics and ideals in that we need to find our own language, not a borrowed one. From this also stems the concern of function in ceramics. My work however is situated in the obscure boundary between utilitarian and symbolic use. The functionality of the work is not inherently obvious. Its intention is to draw on much weightier notions of the Art/Craft debate. The vessel is no longer a designated symbol of functionality as the works are embedded with these multi-narratives.

Petra Svoboda, Randwick NSW

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