"The blue material, after it has been roasted, must be specially selected, and there is a particular class of workmen whose duty it is to attend to this. The superior kind selected is that which is dark green in color, of rich translucent tint and brilliant aspect. This is used in the imitation of antiques, for the monochrome blue glaze, and for fine porcelain painted in blue.
When of the same dark-green color, but wanting somewhat in richness and luster, it is used for the decoration of the coarser porcelain made for sale. The remainder, that has neither luster nor color, is picked out and thrown away.
When the material has been selected it is ready for use. The method employed is to paint with it upon the piece that has not been fired, to invest the piece afterward with glaze, and then to fire it in the furnace, from which it comes out with the color uniformity transformed into a brilliant blue. If it has not been invested with glaze the color will be black. Should the piece be overfired, the blue of the painted decoration will 'run' into the white ground of the piece.
There is one kind of blue, commonly called onion sprouts, which makes very clearly defined strokes that do not change in the furnace and this must be selected for fine painting.
The picture shows baskets filled with boxes of the color, with an ordinary background; there is no actual reference in it to the selection of the color."
