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One technique you may not have used is multiple firings. Some people fire a single piece 3, 4 or even more times until they get exactly what they like. The only rule in multiple firings is that you can’t re-fire at a hotter temperature than a previous firing, or you will burn off the lower temperature glaze..
Here is an example of a multiple firing pattern using a Cone 6 or higher clay:.
First glaze firing at Cone 6 (Base glaze).
Second firing at Cone 6 (Maybe you didn’t like the way your original turned out, so you touched it up, or by experimentation you have found that glaze overlaps are nicer when the first is fired and the second added and refired.)
Third firing at Cone 04 (To add accent colors using low fire glazes. Since low fire glazes come in so many bright colors, and “what you see is what you get”, this is a great way to add a variety of colors to your piece.)
Fourth firing at Cone 018 (to add metallic or lustre overglazes in very specific areas.)
I have heard of people firing the same piece up to 10 different times. Sometimes they just aren’t happy with a piece, so they add more and refire. Other times it is a deliberate plan. That many re-fires can start to weaken the clay, depending on the temperatures and the clay bodies used.
It gets a little more complicated with reduction firings, including Raku. Since these firings need a lack of oxygen in order for the glazes to develop, you can’t refire them in an oxidation firing (electric kiln) or all the reduction you did will be reversed. For example, in Raku, carbon causes the clay to go black where it isn’t glazed. If re-fired in an electric kiln, the black will burn out and you will get the clay color where it is bare. Reduction and Raku glazes may or may not look good re-fired in oxidation, but they will probably look different.
I took a workshop with Kevin Myers where we did Raku, followed by china painting on certain areas. We focused mainly on painting within the lines of crackle that had been created by the first firing. Kevin had several pieces with pops of bright orange color added in this way. We then re-fired in the Raku kilns just long enough to fix the china paints and allow the glaze to re-melt so it could be re-oxidized. We couldn’t over fire this second firing, or the china paints would burn off. And after the re-fire, the pieces had different patterns because they had oxidized differently (depending on how oxygen starved the piece was, where the pieces of newspaper landed, etc.) One thing we were able to do on the second firing was hold newspaper directly up to the crackle glazes and get more crackle.
So next time you have a piece that you like but is a little bland, try brightening it up with some accents, and re-fire!
Overglazes are available in both water based and oil based forms.