Techniques

I have continued my raku work this year and have recently started to explore high-fired glazes on stoneware and porcelain, in particular Chun glazes which are fascinating…and unpredictable.

In preparing the raku pieces, once thrown they are left to dry, then burnished and, in most cases, coated on the outside with terra sigillata, a fine slip coat, which provides a smooth, shiny finish and excellent absorbent outer surface for smoke and fumes. The only exception is where they are to be fully glazed, in which case they are just lightly burnished.

Pit firing


I have had a lot of fun exploring this technique recently. Strictly speaking these are bin firings, but the effects are the same as those produced by the more traditional pit firing.
The first stages are as above – burnishing, terra sigillata and electric firing. The pieces are then coated with ferric chloride, then wrapped in cloth which has been soaked in copper salts and dried. This bundle is then placed on a base of wood, paper and sawdust in a small bin, covered with more paper, sawdust, salts and sometimes organic matter such as seaweed or corn husks. The bin is set alight and left to burn for several hours. Once cool, the pot is removed, wiped with a dry cloth, then polished with crystal wax.

Metallic glazes and lustres

Pieces are fired to 975 in an electric kiln then brushed with a lustre glaze. They are then fired to 975 – 1000 in a gas-fired raku kiln, removed after just a few minutes cooling temperature and placed in a bin of shredded paper and sawdust for 10 – 15 minutes to promote reduction and produce metallic effects and lustres.

Chun glazes
Chun glazed bowl 1

The pieces are thrown in stoneware or porcelain the glazed with a chun base then a chun glaze, sometimes with the addition of copper oxide. The pieces are fired quickly to 1240-1260C. The glazes are free flowing and unpredictable, but when they behave they produce some wonderful effects.

Naked raku

A complex but dramatic technique which produces excellent contracts of black and white. Pieces are burnished and coated with terra sigillata, a fine slip coat, which provides a smooth, shiny finish and excellent absorbent outer surface for smoke and fumes. After a first firing to 975 degrees in an electric kiln the pieces are dipped in a resist slip (some having been masked with tape), then once dry are dipped again in a white crackle glaze. The pieces are then fired to 950/975 in a gas-fired raku kiln and taken from the kiln immediately and placed in a bin of shredded paper and sawdust for 5-10 minutes. On removal, the ‘sacrificial’ layers (resist slip and glaze) fall away, revealing the smoke marks on the surface of the piece. A finishing layer of crystal wax is applied to protect the surface and bring out the shine.

 Ferric fuming

A fast firing technique that produces a range of colours which are very sensitive to temperature – a few degrees can make the difference between a strong yellow and a salmon pink. The first stages are as above – burnishing, terra sigillata and electric firing. The pieces are then coated with ferric chloride and wrapped in an aluminium foil saggar. A very fast firing to anywhere between 625 and 700 degrees is followed by immediate removal from the kiln and exposure to air. Once cooled, the pots are given a wax finish as above.

 

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