3. A permanent pigment added to a semi-stable pigment yields a semi-stable mixture. 4. A permanent pigment added to a fugitive pigment yields a fugitive mixture. Consequently-- 5. A permanent pigment may be rendered fugitive or semi-stable by improper compounding. 6. A semi-stable or fugitive pigment is not rendered durable by being compounded. 7. As a chain is only as strong as its weakest link, so a mixture is only as permanent as its least durable constituent. To give illustrations-- 1. Ultramarine added to Chinese white yields a permanent mixture. 2. Ultramarine added to an acid constant white yields a semi-stable or fugitive mixture. 3. Ultramarine added to Prussian blue yields a semi-stable mixture. 4. Ultramarine added to indigo yields a fugitive mixture. Except in the second instance, where the blue is either partially or wholly destroyed--in time, be it remembered, not at once--according to the quantity and strength of the acid in the white, the ultramarine remains unchanged. Hence at first sight our third and fourth conclusions may appear wrong; inasmuch as, it may be argued, a blue mixture cannot be semi-stable or fugitive when blue is left. To this we reply, unless both constituents are fugitive, a mixture will always more or less possess colour; but, if even one constituent be semi-stable or fugitive, a mixture will slowly but surely lose _the_ colour for which it was compounded, and be _as a mixture_ semi-stable or fugitive. It need hardly be observed that the number of permanent orange, green, and purple hues which the artist can compound, depends mainly on the number of permanent yellows, reds, and blues at his disposal. In mixed orange, therefore, a selection of durable yellows and reds is of the first importance. It should, however, be remarked that mixed orange, more sober and less decided, is obtainable by the use of citrine and russet; in the former of which yellow predominates, and in the latter, red: consequently orange results when yellow is added to russet, red to citrine, or citrine to russet. PERMANENT YELLOWS. | PERMANENT REDS. | Aureolin. | Cadmium Red. Cadmium, deep. | Liquid Rubiate. Cadmium, pale. | Madder Carmine. Lemon Yellow. | Rose Madder. Mars Yellow. | Mars Red. Naples Yellow, modern. | Ochres. Ochres. | Vermilions. Orient Yellow. | Raw Sienna. | None of these pigments react on each other, and from them can be produced the most durable mixed orange that yellow and red will afford. 161. NEUTRAL ORANGE,