_Rose Rubiate_, or _Liquid Madder Lake_, is a concentrated tincture of madder of the most beautiful and perfect rose colour and transparency. It is used as a water colour only in its simple state, diluted with water, and with or without gum. In oil it dries by acting as a siccative. Mixed or ground with all other madder colours, with or without gum, it forms combinations which work freely in water, and produce the most charming and stable effects. The rubiate also furnishes a fine red ink, and is a durable stain for printing on cotton, &c. To the tinting of maps and charts permanently, it is peculiarly suited. 81. MARS RED Or _Rouge de Mars_, is an artificial iron ochre, similar in subdued tint and permanence to the native earths. Its chemical affinities, however, are greater than those of the latter, and it therefore requires to be employed cautiously with pigments affected by iron. In this respect the red resembles its compeers, Mars yellow, Mars orange, Mars violet, and Mars brown, all of which are iron ochres artificially prepared. Possessing the richness and depth of Indian red, it is distinguished by the russet-orange hue of light red. Its pale washes are marked by considerable clearness. In keeping the Mars colours separate from the ochres, we have followed the plan of the author. OCHRES Comprise _Red Ochre_, _Indian Red_, _Light Red_, _Venetian Red_, _English Red_, _Persian Red_, _Prussian Red_, _Spanish Red_, _Brown Red_, _Indian Ochre_, _Scarlet Ochre_, _Carnagione_, _Terra Puzzoli_, _English Vermilion_, _Spanish Brown_, _Majolica_, _Redding_, _Ruddle_, _Bole_, _Almagra_, _Sil Atticum_, _Terra Sinopica_, &c. They are rather hues and tints than definite colours, or more properly belong to the tertiary, semi-neutral, and broken colours. As a rule they are native pigments, found in most countries, and very abundantly and fine in our own; but some are products of manufacture, and obtainable in the variety of nature by art. The colouring matter of these earths is the red oxide of iron, as that of the yellow ochres is the yellow oxide. All the yellow ochres are more or less reddened by being burnt, as yellow oxide of iron itself becomes red on calcination. It was observed in the fourth chapter that time has often the effect of fire, more or less intense; and hence it is that yellow ochres occasionally assume a buffish-red hue, by the gradual peroxidation of the iron. Similarly, if a yellow ochre be but partially calcined, the red so obtained is apt to deepen or darken. Especially do these changes take place when the iron oxides are not associated with an earthy base; when, in fact, the so-called ochres cannot be classed as such. In this case, too, as was lately remarked, the pigments are more chemically active, and more likely to affect those colours to which iron is inimical. 82. RED OCHRE