Page:Cyclopedia of Painting-Armstrong, George D (1908).djvu/126

118 by aid of a blow-pipe. Take a piece of flat charcoal and cut out a hollow space from it into which place a small piece of white lead to be tested, about the size of a pea. Now direct the flame of a blow-pipe upon it, using an ordinary candle or a Bunsen burner, taking care that the blue portion of the flame bears upon the lead. Keep up a steady blow for a few minutes and the white lead will be converted into metallic lead, which will show in the form of a bright silver-like button. If the lead is adulterated the blowing will only have the result of making it appear like a cinder. To conduct this experiment successfully requires a little practice with the blow-pipe in order to obtain a steady flame.

Another method of testing is to place a little white lead in a crucible and place this on a hot fire, when, if genuine, it will be converted into metallic lead.

Purity of Tone. Some remarks on this subject will be given under the heads of the various groups of colors. Speaking generally, the richness of brilliancy of tone is easily discernible by placing the sample to be tested side by side with another of well known excellence. In siennas, ochres and umbers the selection of crude material by which the richness of tone is assured is of great importance.

Fineness of Grinding. The method of testing the fineness of a pigment usually employed by the painter is to rub a little on the finger nail, but this is a crude and unreliable method. If the pigment is dry and it is desired to compare it for fineness with a similar pigment or white lead, the following is as good a plan as any:

Take two tall vertical glass jars, place in them an equal quantity of turpentine and then take a small quantity of the white lead to be tested. Place it in one jar, and an equal quantity of the pigment with which it is to be compared in the other; thoroughly stir up both and then note the time it takes the sample to settle. If graduated marks are made to the two jars the observations will be taken more readily.