RAW UMBER

An ochre containing manganese oxide and iron hydroxide. Because of the manganese content it is an excellent dryer. It can be used in all techniques but requires 80% oil, with an additional 2% wax when in tubes to prevent hardening. The best variety is sold under the name of Cyprus umber, which comes chiefly from the Harz mountains. Many umbers have a greenish tinge, and in acids it dissolves in part leaving a yellow solution; hydrochloric acid gives it an odor of chlorine. In alkalis it discolors a little and when heated, becomes a reddish brown. Burnt umber has the same properties as natural umber. In oil both tend to turn dark later on, especially if the underlayers were not thoroughly dried, but this darkening may also occur in alla prima painting. Burnt umber turns especially dark, surprisingly as the burnt tones are usually more reliable in this respect. Here again, the tendency to darken is increased by the modern practice of grinding the tube colors too finely. Its best not to use the color in fresco, as in the open it tends to decompose and the produces a burnt heavy tone.

REALGAR

The first cousin of orpiment, both being a sulphide of arsenic; realgar being an orange-scarlet, to orpiments yellow. Realgar however, was not common in medieval paintings, with references limited largely to preservation of glair, and only sometimes used as a pigment. Cennino mentions it without any real enthusiasm, it is not mentioned often concerning book paintings, and it has not been identified on any panels.

RED AND LAC LAKES

The work "Lake" in pigments derives from a material known as Lacca from which they were prepared. We don't know what was meant by lacca but have supposed that was the material we now call Lac, the gum lac of India, a dark-red encrustation of resin which is produced on certain kinds of trees by the sting of certain insects. This gum, or rather resin, is the source of our shellac. If the crude material is boiled with water and a little alkali, the coloring matter dissolves in the water; it is dried and sold (rarely now) as "lac dye". This is used for painting, or a lake can be colored with it. The one pigment still made with it now, is called Indian Lake. The colors that lac dye produces are generally violet, and not very brilliant. Cennino advised beginners "for their great pleasure, always to start by doing draperies with lac." This was primarily a panel painting color; too dark and dull for books, and not stable enough for walls. Lakes in general were not highly regarded as other colors could make the same dark, purplish earth reds with much more stability. Cennino 1400: "A color known as lac is red. And I have various receipts for it; but I advise you, for the sake of your works, to get the color ready made for your money. But take care to recognize the good kind, because there are several types of it... Get the lac which is made from gum. And it is dry, lean, granular, and looks almost black, and it has a sanguine color. This kind cannot be other than good and perfect... It is good on panel; and it is also used on the wall with a tempera; but the air is its undoing".

RED LEAD

Also known as minium

RED OCHRE

A version of iron oxide which contains clay in varying quantities, and silica. It is an important natural pigments which has been widely used; mostly known as the red paint of the American Indian, and Sinopia of classical antiquity (see sinopia for more information). The best examples of the pigment contain as much as 95% ferric oxide.

RHAMNUS YELLOW

The berries of buckthorn known as rhamnus, were gathered when they were ripe, yielding the color now known as sap green. When gathered before ripening, they yielded a yellow color; the compound of their unripe juice with alum was not much used, but was recorded in the sixteenth century under the name berry yellow. The fourteenth century method was to use the verjuice alone in its natural state to enrich mixed greens. In the course of that century in Italy, yellow lakes began to be made from the unripe berries, and they were popular in the fifteenth century under the name of giallo santo, or holy yellow. Their popularity increased in later centuries despite their lack of permanence, and were very much in vogue in eighteenth century France and England. rhamnus berries are still sold, dried, under the name of graines d'Avignon, or Persian berries.

RHODAMINE

Discovered by Bernthsen in 1892, this is one of the more stable synthetic dyestuffs used for making red lake pigments, and is the ethyl ester of diethyldiamino-o-carboxy-phenyl-xanthenyl chloride.

ROSE CARTHAME

The French name for Rose Madder.

ROSE DORE

A weaker and less stable Madder Lake.