Читать книгу The Mixing of Colours and Paints - F. N. Vanderwalker - Страница 7

Table of Contents

Among the first color pigments used by man in the early stages of civilization and, indeed, during the savage ages, were colors which were nothing more than natural deposits of colored earth found in many parts of the world. The colors of these earth pigments are due to their content of more or less oxide of iron and other mineral substances. As a class they are permanent in color, durable and economical.

The principal earth colors are raw umber, raw sienna, yellow ochre, mineral browns, venetian red and Indian red—the last two are now made by chemical processes. These are used just as they are dug out of the ground after washing and screening to eliminate roots, stones, etc. They are dried and ground to make them fine and are classified according to shades of color. Next they are mixed or ground in linseed oil or water, or Japan to make them ready for the painter.

The earth colors are also burned, or calcined, to change their colors. Raw umber which is a dull, grayish brown, becomes a deep chocolate brown when calcined and is called burnt umber. Raw sienna, a rather dull yellow, becomes a cherry red in the burning process and is then called burnt sienna.

Raw Sienna.—One of our most valuable colors, an earth pigment, named after the city of Sienna, Italy, near which natural deposits of an especially bright and clear yellow raw sienna earth were found. These were very fine, rich and transparent colors of great beauty and permanence. When mixed with a white base, clear and delicate tints result.

Sienna earth is found in pockets surrounded by earth of a different character. It owes its color to hydrated silicate of iron, probably precipitated from ponds and bogs containing a solution of iron and silica. There are great variations between different deposits as to brightness of color, texture, fineness and freedom from sand and stone. High quality raw sienna is essentially a yellow ochre of great purity as to color. It is not only brighter in color but has greater tinting strength than yellow ochre and so produces clearer tints when mixed with a white base. It is not muddy, or cloudy like yellow ochre, but quite transparent, which makes it valuable for mixing stains, graining and glazing colors. Both raw and burnt sienna are in the group of most permanent colors known and have been used for hundreds of years.

Burnt Sienna.—Made by roasting raw sienna, which process changes the yellow color to rich brownish red. Burnt sienna, when properly roasted, possesses substantially the same qualities as the raw sienna from which it is made, and is used for the same purposes in decorating and tinting where clear reds and pinks are wanted.

Raw Umber.—Italy claims the origin of umber as well as sienna. The color takes its name from Umbria, Italy. However, in modern times the island of Cypress, in the Mediterranean Sea, appears to be in possession of more deposits of this drab earth color. It has been marketed through Constantinople and so gained the name of Turkey umber.

The characteristics and history of umber are much like sienna. The difference in color is due to its content of a large percentage of manganese in addition to oxide of iron. This possession of manganese makes the umbers very good drying colors—raw umber, in fact, is used in the manufacture of liquid driers.

Raw umber in color is a dark, greenish brown. It is almost transparent, has great tinting strength and produces clear tints when mixed with white.

Raw umber is very durable, permanent to light and invaluable for mixing dark greens, olive greens and cold drabs which are more permanent in strong light than those mixed from chrome green alone. Some of the umbers possess a reddish rather than a greenish tone and, of course, are not cold, but warm colors not so suitable in the mixing of greens.

Burnt Umber.—Substantially the same as raw umber except for color. The calcining or roasting of raw umber changes its color from a greenish brown to a deep chocolate brown. This warm brown makes burnt umber a valuable color for tinting a white base to tan and many other useful colors in paints. It is a quite transparent color and so is extensively used for mixing stains, for glazing color and for graining.

Yellow Ochre.—In this color we have another earth pigment. And it is doubtful if any color is found on the market having greater variations of quality. The name yellow ochre on a product may mean any one of several materials or grades.

Deposits of yellow earth are found broadly distributed over the earth's surface in the form of sand or clay. Not many of them have any real value as a color or paint pigment.

In France deposits of the best quality yellow ochre are found and they are very similar to raw sienna. High grade French yellow ochre is clear and bright, as to color, but cannot be used as a glaze, stain or graining color. It is durable and permanent in strong light. Domestic and some other foreign yellow ochres are muddy and dull in color; they have not the tinting strength of French ochre and have but little in common as a color, paint or tinter with French ochre.

Correctly made yellow ochre is one of the most useful tinting colors, but unusual care must be shown by manufacturers in washing, floating and separating to eliminate coarse sand, if a color with good tinting strength is to be produced.

Yellow ochre is the body, the solid opaque yellow of nature, while raw sienna is the transparent yellow which can be used as a glazing color and a stain.

For the mixing of yellow tints—tans, creams, buffs and olive green—good French yellow ochre has no superior; it is durable, fast to light and economical.

Vandyke Brown.—An earth pigment of a rich, deep brown similar to but richer than burnt umber. It takes its name from the old Dutch master, Vandyke, who used the color with remarkable effect. It is of bog origin and contains iron and bitumin. As made today Vandyke brown is quite permanent, is an excellent tinting color and so transparent that it is invaluable as a glazing and graining color where a richer brown than burnt umber is needed. It is unsurpassed for glazing old bronze effects and for staining to imitate old English, antique and bog oaks. Used to color a white base, the tints have a lavender tinge to them.