This Month’s Raku Glaze of the Month is a little different than usual. We so enjoyed our recent workshop with Wally Asselberghs and Sue Morse, we decided that rather than highlight a specific glaze on our shelf, we would instead highlight the techniques and materials needed for both Naked Raku and Ferric Chloride fuming.
Wally identifies a “technically perfect” sacrificial slip layer form David Roberts, which consists of 60 parts EPK and 40 parts Silica. However, because the recipe has no suspender, it needs constant stirring. To adjust for this, Wally combines one part of this slip recipe with one part potters clay (The clay is first dried out, then crushed into powder to mix with the dry slip mixture. After mixing, the slip is sieved multiple times, ultimately through at least an 80 mesh sieve). In Belgium, he uses a Limoges Stoneware. At Bracker’s we used our cone 5/6 Buff. Wally applies the slip layer either by burshing, dipping, spraying or pouring.
On top of the slip layer, Wally applies a glaze using a variety of techniques from spraying, dipping, pouring & brushing, to splashing, sgraffito, sponging, spattering, and masking. The glaze he uses is a recipe from Bill & Kate Jacobson, which consists of Gerstley Borate and Frit 3110. He mixes some up to a “classic” consistency (roughly a one to one ratio by weight), some to a thick consistency and some to a thin or diluted consistency. The thicker version is what Wally would use for splashing while the thinner diluted glazes would typically be brushed on. The thickness will also determine the percent of grey that will result in the final product.
The Naked Raku process is much cooler than one typically expects with Raku. After an initial preheat, the kiln is heated slowly up to 600ºCelcius (1100ºF), then faster from there to about 725ºC (1325ºF), then a bit slower up to about 775ºC (1450ºF), then held there while the orange peel look becomes uniform (approx 5-10 minutes).
The pieces are then pulled and placed into reduction chambers for 5-10 minutes, then cooled down with a fine mist of water (spray bottle), then the outside layer of slip is scraped off, the piece is cleaned thoroughly, then a layer of wax is applied.
Wally’s technically perfect slip (add your own clay) is available this month for $2.00/#
The basic glaze recipe is available this month for $3.00/#
In contrast to the Black and white and shades of Gray Naked Raku was Sue’s Ferric Chloride Fuming. From Sue:
This is a simple technique that utilizes ferric chloride (FeCl3) to create rusts, pinks, browns, creams, and burgundies. Additional materials may be added to influence the colors and surface textures such as salt, fertilizer, seaweed, horse hair, copper and steel wires, organic materials, etc.
Pots should be prepared with clay that can withstand temperature shock. I use stoneware. The pieces can either be well burnished and/or coated with terra sigillata, or left rough. The lower the bisque temperature, the better the burnished shine remains. I bisque to cone 010, which is roughly 1650ºF (900ºC). Smooth surfaces are enhanced with a final application of wax.
Ferric chloride is a corrosive chemical and should be handled with respect. It is also called Iron Chloride. It is soluble in water and alcohol and is non-combustable. It can be obtained either as a solid (not recommended as it can give off highly toxic hydrogen chloride fumes when mixed with water) or in liquid form.
Precautions necessary when applying it to your surfaces are to use goggles and gloves, keep the solution in a plastic or glass container, and wash off any liquid on the skin with water. It also stains clothing. However, during the firing process (fuming) toxic gases are present and a respirator is highly recommended for removing the pots from the kiln and for removing the aluminum foil.
We used a lump reagent grade Ferric Chloride that must be obtained from a laboratory supply company. They will only ship to a business. For a limited time, Bracker’s will accept orders for Ferric Chloride, order it to come here and then ship it out to you. We will be accepting orders through November, and the product should come in in December.
The special “Glaze of the month” price on Ferric Chloride will be $2.00/gram in 10 gram increments.
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