Originality of Koyo roof tiles
Traditional Japanese quality roof tile.
In the manufacturing process of tiles, ‘loading the kiln’ and ‘polishing’ are particular to Koyo tiles. As our tiles are unglazed, polished surface shines with Ibushi silver. As the green bodies will become the finished surface, the quality of tile depends on accuracy of polishing. Although the polishing is often skipped when we think about the cost but at Koyo Seiga, we keep the tradition of polishing. For “loading the kiln”, we use the traditional “Yokka Gama” which literally means firing for four days. As a result of slowly firing and slowly cooling, the strong Koyo tile, which is resistant to break, is born.
Manufacturing process of Koyo Kawara
With Koyo tiles, the technique which is more than 100 years old is inherited. All the manufacturing process such as polishing the surface of tiles and firing for four days are all done by hand.
Mix a few different types of clay and then crush. Add water to it then wedge while removing air
2.Cut the clay using the mold
Cut the clay to size of tiles then make green body called Araji.
First step to make the quality tile is to keep the humidity steady. Other Kawara producers are diving laboring process but at Koyo Seiga, more than 350 different Kawaras are made all by ourselves.
3.Press the clay and mold
Put the green body to the pressing machine to mold. Adjust the tile assuming the shrinkage and distortion after firing.
Polish the surface by using a rib and spatula
Set the tiles next to kiln and dry by using the heat from it. Adjust according to the temperature and humidity.
Compared to the general kawara is fired for 1 to 2 days, we use the method of “Yokka Gama” which means 4 days kiln.
We increase slowly the fire up to 1165℃ to tighten firmly.
A process to fix the carbon film on the surface of tiles to make Ibushi silver.
After completely burn out the iron in the clay, we do the reduction by smoking.
If iron remains in the clay, it will cause rust.
Remove soot on the tiles one by one by hand.