I prefer light coloured clay containing grog. The color of the clay, combined with the application of a transparent glaze on the desired parts, allows to obtain white cracked zones during Raku firing. As to the grog, it confers resistance and body to the clay.
Handbuilding of the Pieces
The first step is to turn the raw clay into slabs, using a slabroller. The slabroller is a machine with two rollers that progressively compresses the clay at each pass, thereby allowing to obtain slabs of uniform thickness.
After creating an outline of the desired piece, the sections that compose the piece are carved separately out of the clay slabs and assembled using slip and small coils.
Pieces are then dried slowly under a plastic sheet, to avoid the formation of fissures. Once the pieces reach the leather state, it is recommended to polish them using a spoon to close up the clay’s pores and give it lustre.
Then, firing the pieces a first time transforms them into the bisque state. At this stage, they are solid, but still very porous.
The next step is to apply glazes for the Raku, using either a brush or a spray gun. Glazes are mixtures of substances in suspension in water. Each of those substances has a specific role: degrease, melt or darken. The mixture of salts and metal oxides in the glazes determine its colour, such as copper red, cobalt blue or shiny green.
As a point of note, area of pieces with no glazes will turn black after Raku firing, due to the carbonisation of the process.
The Raku Firing Method
For firing day, I prefer a sunny day, but not too hot nor too humid.
In the morning, the first step is to install the propane gas kiln and to do a dry run without pieces, in order to eliminate moisture in the kiln. Vats containing wood chips as well as a water basin are placed at proximity.
The pieces are fired one batch after the other, at a temperature of 1,950 degrees F. When the desired temperature is reached, the pieces are promptly taken out of the kiln using grips and placed into the wood chips vats. Upon contact with the pieces, the wood chips ignite. The fire is then smothered by fully covering the piece with additional wood chips and putting a lid on the vat.
Because much smoke is liberated during this process, it is recommended to use protective equipment including mask and goggles.
See pictures of the firing process
Finale
After a leaving the pieces rest in the combustion vats, they are taken out and plunged into the water basin for a last thermal shock. Only at that moment do we know if the pieces endured all the treatments. The piece will be lost if a suspicious crack produces a vibrating sound when tapping it. Small cracks are however desired to give an oldish style to the piece. The carbon from the combustion infiltrates these cracks and colors the bare clay in black.
The metallic colors on the pieces are primarily determined by the composition of the glazes. However, these colours will vary from one batch to the other depending on many factors:
- Shape of the piece
- Piece location within the kiln
- Way the flame licks the piece during firing
- Unloading time
- Way the pieces are covered with wood chips
- Time spent in the combustion vats
- Way the pieces are plunged in water
A repetitive and rigorous method ensures more control over the final colors, but there are always surprises and amazement.
Paper Clay
C’est une pâte très intéressante lorsqu’on veut obtenir de la légèreté et de la délicatesse. Elle résiste au fendillement en séchage rapide, elle se juxtapose facilement couche sur couche et on peut même appliquer de la terre humide sur de la terre sèche.
Je l’utilise pour faire des murales composées de couches superposées. Je me sers de coton fromage imbibé de barbotine pour texturer le tour ou le centre de la murale. À la cuisson, le papier présent dans l’argile et le coton fromage brûlent. Il en résulte une céramique d’une grande finesse.
Copper and Patina
The patina is formed through chemical reactions on the metal’s surface. With copper, colors vary from brown to green or blue, similar to the roof of certain old buildings. With my techniques, these chemical reactions are accelerated, as it would take as much as 50 years to obtain these colors with the action of acid rains alone.
In my mural pieces, the patinated copper is used as support structure. On the other pieces, it is affixed in the form of embedded platelets. This step is done after the firing.
