Kaolin rocks of Izumiyama are open cut. The rocks are
wasted in water, cracked with a hammer, and sorted according to the quality
of their cracked surfaces. Today, kaolin rocks from Amakusa are also used.1 Quarrying
Kaolin rocks of Izumiyama are open cut. The rocks are
wasted in water, cracked with a hammer, and sorted according to the quality
of their cracked surfaces. Today, kaolin rocks from Amakusa are also used.
2 Crushing
Kaolin rocks and crushed, then ground to fine powder
with a stamper.
3 Precipitating and filtering
First, kaolin powder is mixed with water. Then the
solution is precipitated and its supernatant fluid flows in a long tank
and is filtered with a fine mesh to remove iron ingredients and other impurities.
Thus good kaolin clay is obtained, which is easy to form.
4 Filter-pressing
Extra water is removed to make clay of adequate firmness.
5 Clay kneading
Clay has to be kneaded well to blend its particles
and moisture and to remove all bubbles. Articles made of well-kneaded clay
will not crack or distort when fired.
6 Forming
This is the most important operation in the entire
process of porcelain manufacturing. Most of Arita's porcelain is formed
by using lathes.
7 Body decorating
Various decorative techniques as carving, lines engraving
by using a comb, cutting holes, adding small knobs, etc., are performed
on the articles at the appropriate degree of dryness.
8 Paring
At this stage, the formed articles are still moist
and must be finished by hand paring. According to the shapes of the articles,
bottom rim paring, surface paring, knob making, edge finishing, and other
finishing touches are added.
9 Wiping
The surfaces of the articles are carefully wiped with
wet cotton cloth or deer skin until extremely smooth, before the under-glazing
and glazing are applied.
10 Drying
If the articles are dried quickly, cracks may occur
due to shrinkage. So the articles are put on long boards and allowed to
dry in the shade or the sun.
11 Low-firing
Prior to high-firing, the articles are low-fired. The temperature inside the kiln is gradually Low-firing is done at 900c.
12 Removal from kiln
The low-fired articles are gradually cooled in the kiln, and then taken out and carefully inspected.
13 Underglaze mixing
The most important operation of the porcelain painters
is to determine how to mix the underglaze with water. There are two kinds.
One is for drawing (outlining patterns) and the other it for painting (filling
in of shading the pat terns).
14 Underglazing (drawing)
"Gosu" is used as blue underglaze. The main
ingredient is cobalt oxide. After firing gosu turns blue. Low-fired articles
absorb water, so that it is difficult to draw or paint on their surfaces
with brushes. The quality of the finished porcelain is determined by the
Painter's skill.
15 Underglazing (painting)
Big brushes are used to apply the blue paint inside
the patterns. Some parts are shaded. This technique is called "dami"
16 Glaze making
Glaze is a thin film covering the surface of the article
Which becomes glass after firing. Its ingredients are feldspar, limestone,
silica, ash from the "yusu" tree, and various other substances.
17 Glazing
Small articles are dipped in a glaze tank. Big articles
are glazed by using a dipper called a "choppage" in Japanese,
to pour the glaze over the object.
18 Glaze finishing
The glazed surfaces are carefully checked to be sure
they are smooth. The glaze on the bottom of the article is pared or wiped
off so that the article won't adhere to the tools inside of the kiln during
high-firing.
19 High-firing
When high-fired the clay and glaze are matured and
porcelainized, resulting in beautiful porcelain. There are three stages
of high-firing. At first, kilns are gradually heated to 900c, then rapidly
heated to 1,200 and finally the temperature reaches 1,300c.
20 Removing from kiln
White porcelain without colored patterns called "hakuji"
in Japanese, blue and white porcelain called "sometsuke", celadon
porcelain called "seiji" and dark blue porcelain called "ruri"
are completely finished at this stage. The others require further processing
described next.
21 Over-glaze mixing
There are many colors of over-glaze such as red, yellow,
green, black, gold, silver and so forth.
22 Over-glazing
The over-glaze is painted on the vitrified glaze. Like
under-glazing, the drawing technique and shading technique "dami"
are also used here.
23 Fusing
Over-glaze is fused to the porcelain in kilns fired at a low temperature(720-830c).
24 Products
Thus the finished porcelain is called "iroe",
"akae" and "somenishiki" according to its pattern.