Mars Spectrum Raku Glaze Ref.SPEC/865
Raku glazes were developed for firing in either electric or gas kilns. The firing process is described below. Three of our Raku glazes are not lead-free (857,858, and 867 contain lead and cadmium). Four of the Raku glazes are lead-free and non-toxic (850,851,854, and 856). All of the rest are lead-free, but are over the threshold limit for copper and are therefore not non-toxic in the liquid state. Our liquid glazes (available in 4 ounce, pints) are set up for brushing application. They can also be poured or dipped on pieces, although they should probably be thinned with a little water for this type of application.
Raku glazes should be fired up to cone 06 (999C) in either an electric or gas kiln. They they should be allowed to cool in the kiln to 760C. While still red hot they should be transferred as quickly as possible into a reduction bin (typically a metal garbage can or small metal container with a lid that has been lined with organic material such as newspaper and/or sawdust, etc.)
As soon as the pieces are in the bin the lid should be put on to keep oxygen from entering the container, in order to develop the reduction atmosphere. The pieces should be allowed to cool in the bin for at least 20 minutes.
When the red hot pieces go into the bin, the organic material ignites producing flames and smoke so this part of the firing should be done outside.
Try to size the reduction bin to the size of the piece being fired.
Position the organic material and the piece so that the flames can get all around the piece.
Different organic materials can produce very different results, so for example a glaze reduced in newspaper could be a beautiful blue color and the same glaze reduced in sawdust could have a metallic copper appearance.
Pieces should be cleaned immediately with water and a hard bristle brush.
After cleaning, warm the pieces in the kiln to evaporate any water from the piece. This helps to set the colors more permanently.
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