Copper red glazes require tight control of the reduction firing. The mug on the left is grey and brown by the foot, the other has developed no color at all on some parts. These were fired to cone 10R with reduction starting at cone 010 and going all the way up. There was no clearing or soaking period at the end of the firing. This is the Red Celadon recipe.
The color red is very difficult to achieve in ceramics. The most vibrant red within the reach of the average potter is the color produced by copper in reduction firing.
A method of firing stoneware where the kiln air intakes and burners are set to restrict or eliminate oxygen in the kiln such that metallic oxides convert to their reduced metallic state.