What we. know as burnt Turkey umber is the Cyprus raw umber, burnt or calcined in the lump form and is imported into this country in this as well as in the powdered form. It runs from light reddish brown to a violet brown, its tone depending upon the nature of the raw material it is calcined from. The roasting or calcination drives off some of the combined water in the raw material and imparts a warmer tone, deeper color and more translucency to the pigment.
It is scarcely worth while to dwell in detail on the chemical constituents of burnt umber, as they are practically the same as in the raw pigment, with the exception that the combined water being present in a reduced percentage, the other constituents will show a relatively higher percentage. Burnt Turkey umber with a reddish brown tone makes a stronger stainer, but the pigment with a neutral tone that leans, when rubbed up in oil, to the olive with a tinge of the violet and produces when used with white a tint that has a suspicion of lavender-gray with its drab effect, is far preferable to the almost terra cotta brown tint produced by some of the reddish toned burnt umbers. The principal feature is a warm, rich brown in the solid color, because this is best for the use of grainers and stainers, where most of the color is really used. American burnt umbers, though there are some very good specimens offered, are unfit for these purposes, being too opaque and not rich enough in color. Nor will it carry enough oil to serve well as a stain. Burnt Turkey umber should be ground on similar mills and at same speed as mentioned for sienna, but the temperature need not be watched as carefully, as the tone is not so liable to suffer from excessive heat. The average percentage of raw linseed oil and pigment may be set down at forty-seven of the former and fifty-three of the latter, while American burnt umber may be mixed and ground in the proportion of 60 per cent pigment to 40 per cent oil, if of good selection. For grinding burnt umber in japan and for artists' tubes, the same rule applies as for raw umber; while for distemper and fresco work, burnt umber is an important part in the list, being used to a very great extent, especially for graining in distemper. It may be mentioned that as a rule burnt umber is not as difficult to grind fine as the raw pigment and buhr mills are not absolutely necessary.
Sepia scarcely interests color grinders in general, as it is mostly used as a water or moist color. It is made from the ink bag of the cuttle fish, the gland so-called, in which this fish secrets the blackish brown liquor for defensive purposes. These bags can be bought in the dry state and boiled in a solution of soda, that dissolves the color, but not the bag. The liquor is then filtered and neutralized with hydrochloric acid, which throws down a precipitate that is washed and dried. Sepia is of a color between asphaltum and Vandyke brown, very strong, and while it will mix with oil, it is hardly ever so used. Still it is almost indispensable on the palette of the artist for water color painting, but is not used in distemper work.
Most of the so-called Vandyke browns imported into the United States are known on the other side as Cassel earth or Cologne brown. They are of organic origin, peat mixed by nature with more or less earthy matter. They have a rich warm tone, generally much darker than the darkest shades of burnt umber, although they vary somewhat in depth and are assorted light, medium and dark. Vandyke brown is not permanent enough when used for tinting, although with white it produces a peculiar lavender gray tint. But it is almost indispensable for graining in oil or water and for staining furniture. Oilcloth makers also use it ground in oil to a great extent, but it is a very slow drying pigment and should be well dried to expel the hygroscopic water before mixing and grinding in oil. Requires to be ground in strong boiled oil or at least the addition of strong drier. Being very light in specific gravity, about 55 pounds of pigment and 45 pounds of oil will make a fair paste, and a 24-inch mill will be the best size for grinding in large batches. When the paste is required to be rather stiff, an iron mill is better adapted than than stone mills. When grinding in japan, a very quick drying coach japan is the best vehicle. It should be also on the distemper color list, as it is used quite frequently for graining, 50 pounds pigment and 60 pounds water will produce one hundred pounds finished product.