Wednesday, April 8, 2009
just to let you all know what goes into ceramics production...
So ceramics need to be fired twice (Yeah, I know, some people do it all in one firing, but that is too unpredictable for my tastes). The first of the firings is called a bisque firing, this takes out a good amount of the moisture, but is not hot enough to vitrify the clay. WHat you see loaded in the kiln is what is called greenware. That just means that the clay has been thrown and allowed to air dry. It is freakishly fragile at this stage and still makes me nervous to handle it. I fire it to cone 04 for my bisque firing, around 1925 degrees F. This is considered low firing. When someone says they use a low fire clay, it is in the range of cone 06- cone 1. It is the most common firing range for ceramics, but also leaves the piece relatively weak.
In a bisgue firing, since the clay is not vitrified or glazed, it is fine to have pieces touch each other or even be placed inside one another. Therefore I get a lot more in the bisque firing than I do in a glaze firing. I pack those bisques tight!
In my little Skutt Electric Kiln, this firing, done on a slow speed will take about 13 hours and about 65kwH of power. I then have to wait for it to cool down, which takes about another 18 hours or so depending on the outside temperature. SO at some point tomorrow, I will take pieces out to wax and glaze them. more on that tomorrow!