Spectrum Raku glazes were developed for firing in either electric or gas kilns. The firing process is described below. Eleven of the Raku glazes are lead-free and non-toxic (850,851,854,856,871,872,873,874,875,877,878). 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. Spectrum liquid glazes are formulated 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. Due to the many variables involved in Raku firing, particularly during the reduction phase, our chip charts and printed color charts should be used only as approximate guidelines. Your results may vary greatly due to different firing conditions. RAKU FIRING – Raku glazes can be fired anywhere from 1600 F up to cone 06 (1850 F) in either an electric or gas kiln. Spectrum recommends firing 850 to 856 and 868 to 879 to a peak of 1700 - 1750 F and 860 to 866 to a peak of 1600 - 1650 F. They should be allowed to cool in the kiln to 1600 F. Different combinations of peak temp and reduction starting temp will produce different results. While still red hot they should be transferred as quickly as possible into a reduction bin (typically a lidded metal garbage can or small metal container 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. WARNING: When red hot pieces go into the bin, the organic material ignites and will produce flames and smoke. This part of the firing, particularly the opening of the reduction bin, should be done outside. Always take safety precautions when firing raku such as the use of high temperature gloves, protective eyewear, and a respirator. Always have a fire extinguisher handy. FIRING TIPS - Try to size the reduction bin to the size of the piece - Establish a good seal to the reduction bin so that air is not entering and smoke is not leaving the bin. - Position the organic material ( newspaper, sawdust, etc.) and the piece so that the flames can get all around the piece. - Different organic materials may produce very different results, 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.
