Part IV: High firing
The next step is high firing. Right now the porcelain is taking its final form.
Ceramics firing is performed in a special kiln which reaches temperatures up to 1350°С. The kiln increases and decreases it slowly enough, according to a pre-set program. For each kind of ceramic, and even type of porcelain, a specific program is required.
Before placing raw porcelain parts in the kiln, they have to be prepared. Inside big ones I put kaolin wool: it’s the heat-resistant material that looks similar to something between ordinary wool and glass wool. Then I put a layer of silica sand, another heat-proof material, on the kiln shelf. The parts are placed on the layer of sand. Later I’ll explain what are all this difficulties for.
Now the shelf can be placed in the kiln.
When temperature reaches about 1200°С, magic happens. . Before firing the porcelain was quite porous and fragile, and during firing particles are sintered displacing the air and forming a homogenous and waterproof material. In addition, the surface of the parts begins to "leak": their surface melt, forming actual glass, called glaze. At this point the porcelain becomes quite soft and can easily be deformed under its own weight. That is why we use kaolin wool and silica sand: wool supports the parts inside, and the sand follows the shape of the parts, and they do not form flat "dents" from the surface they are placed onto.
Correct firing program is very important. If the firing temperature was too low, the surface of porcelain is not leaking, the glaze doesn’t form and porcelain remains porous. At too high temperature liquid glaze literally boils and becomes uneven.
After firing, porcelain gets its final color and satin texture, it becomes translucent and looks like it glows from inside. Besides, due to the displaced air, the parts shrink: they become smaller in volume by about 20-25%.
The firing is completed, the kiln is cooled down, and now we can open it and see smooth, beautiful, sparkling... well, not yet. One side of the parts looks like it should, but another one, the one that was lying on the sand, has to be cleaned off. To do this I soak the items in water and remove the sand with an abrasive sponge.
Work with a porcelain is like magic, is like creation of spells. This material feels as if the artist feels the warmth of their hands and acts by laws known only to it. Even if all the rules are followed meticulously, castings might be defective, even if the basic principles are violated, the details might be perfect. Porcelain has to be understood and felt. For many years I have been working with this amazing material, and each time discover something new.