The usual vehicle for these consists almost exclusively of poppyseed oil, although with permanent red lake, refined linseed oil is probably best, as this color is favored by sign writers and decorators for lettering on glass. The colors for the artists' list in red may be named as follows: - Carmine, carmine lake, chatemuc lake or crimson lake, madder lake, permanent red lake, rose doree, rose madder, scarlet lake, Venetian red and vermilion. Each color must be ground exceedingly fine, yet be of good consistency in order to avoid separation of oil when squeezing the color from the collapsible tube. To avoid waste in filling tubes, a tube filling machine, similar to a sausage stuffer, is best adapted for the work, and the tubes should be long enough to permit of their being closed up at the end by bending over the metal three times.
For Carmine, either No. 40 or amaranth will be of the proper tone, and usually equal weights of color and oil will make the color of the right consistency. For carmine lake a non-bleeding color is required, and the best pigment for this is a cochineal lake that can be ground at the rate of 60 per cent by weight of the lake and 40 per cent by weight of oil. This is simply carmine reduced with a white base.
Chatemuc or Crimson Lake. - These must be non-bleeding and are best made of a mixture of cochineal lake and a wood lake of the type described as being made from sapan or Lima wood decoctions; should require about same proportions of oil and pigment as carmine lake.
Madder Lake and Permanent Red Lake may be of similar composition that is ground from a fine grade of dry alizarine red lake in its own weight of poppyseed or bleached linseed oil, while Rose Doree is natural madder, at least it is made from an extract of the madder root, known as garancine. The dry color is known as lake garance No. 6, and in the dry powder appears rather pink. When ground in oil it is transparent and produces the most delicate pink effects on artists' pictures.
Rose madder may be ground from a selection of very rich alizarine red lake that is utterly devoid of any traces of the brownish tinge usually due to the presence of iron, or it may be ground from true madder of the root. The latter may be tested for genuineness with a solution of caustic soda or potash in which it is very nearly soluble. It will not dissolve in dilute ammonia, but cochineal carmine is soluble in this reagent.
Scarlet Lake is usually a composition of cochineal lake and quicksilver vermilion of palest shade in equal parts reduced with their combined weight of alumina sulphate. Here the proportions of pigment and vehicle are 72 per cent and 28 per cent, respectively.
Venetian Red for this line should be of the brightest type obtainable and be practically pure oxide of iron, ground fine, using 75 parts by weight of pigments to 25 parts by weight of poppyseed or refined linseed oil.
Vermilion for artists' use should be quicksilver vermilion and the grade known as Chinese is the best that can be selected; 86 parts by weight of the dry color to 14 parts by weight of poppyseed oil is about the right proportion for mixing. On account of its heavy specific gravity the pigment separates from the oil in the tubes, and some color grinders have resorted to all sorts of means to overcome this, many using wax with the oil to keep pigment and oil together, and while they have succeeded, the users have had trouble with the color on account of the presence of the wax. A better and safer plan is to grind the pigment in part poppyseed oil and part bodied linseed oil, such as is used in the grinding of lithographers' ink, when the artists can thin the material with some turpentine for easy flowing without impairing the gloss or life of the color.