Bole Almagra Sil Atticum Terra Sinopica &c They Are Rather

: ON THE PRIMARY, RED.

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 o ide. 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.



TTITLE RED OCHRE