"All kinds of porcelain require glaze, and the composition used for glazing can not be prepared without ashes. The ashes for the glaze come from Lo-p'ing-hsien, which is one hundred and forty li to the south of Jingdezhen.
They are made by burning a gray-colored limestone with ferns piled in alternate layers. The residue - after it has been washed thoroughly with water - forms the ashes for the glaze.
The finest kind of petuntse made into a paste with water is added to the liquid glaze ashes, and mixed to form a kind of purée, the proportions being varied according to the class of porcelain.
Within the large jar, in which the mixture is made is placed a little iron pot, through the two handles of which a curved stick is passed, to make a ladle for measuring the ingredients. This is called a p'en. For example, ten measures of petuntse paste and one measure of ashes form the glaze for the highest class of porcelain. Seven or eight ladles of paste and two or three ladies of ashes form the glaze for the middle class. If the paste and ashes are mixed in equal proportions, or if the ashes are more than the paste, the glaze is only fit for coarse ware.
In the picture the little iron pot which is seen floating inside the large jar is the p'en or, measure."
