White Stoneware Tea or Soup Bowl with Copper Red Glaze by Marcello Dolcini, 2019 for sale at Pamono

Description

This glaze is one of the most difficult to manage in high fire pottery: it is called Oxblood (Shinsha in Japanese, Sang de beuf in french). It is a ‘copper red glaze’.

The oxide that produces the color is copper. The cups have been fired in reduction (that means there is no oxygen in the kiln during firing).

Copper is usually green, but if fired in reduction it can become red. Why? during a reduction firing, the flames, that need oxygen to keep alive, try to ‘survive’ at any cost and ‘steal’ oxygen from the pots that are in the kiln. By doing this the flames change the chemistry of clays and glaze present in the kiln. Losing an atom of oxygen, the copper oxide present in the glaze changes its color from green to red.

Only a very little amount of copper (0,3 -0-5% of the glaze) can give such bright reds.

In a reduction firing, not all the parts of the kiln atmosphere are without oxygen. Some oxygen-rich clouds still remain. So if a pot is placed partly in an oxygen-rich atmosphere and partly in an oxygen-reduced atmosphere, it comes with two colors: transparent where there is oxygen and red where there isnt.

These color changes are completely unpredictable and out of the control of the potter. thats why copper red glazes are so prized.

the copper red glaze is a Chinese traditional glaze that was later also acquired in Japan. It was very popular in China in the 15th century. In Europe, these bright red glazes were very prized, and many attempts to reproduced it were made, but without success. The potters in Europe, in fact, couldn’t fire at such high temperatures and didnt know the technique of reduction firing. The first successful attempt was done in France in the late 19th century.