Part 19 (2/2)

2. Hence, though it keeps its colour perfectly when applied in the polished stucco finish of closed apartments, yet in open apartments, such as peristyles or exedrae or other places of the sort, where the bright rays of the sun and moon can penetrate, it is spoiled by contact with them, loses the strength of its colour, and turns black. Among many others, the secretary Faberius, who wished to have his house on the Aventine finished in elegant style, applied vermilion to all the walls of the peristyle; but after thirty days they turned to an ugly and mottled colour. He therefore made a contract to have other colours applied instead of vermilion.

3. But anybody who is more particular, and who wants a polished finish of vermilion that will keep its proper colour, should, after the wall has been polished and is dry, apply with a brush Pontic wax melted over a fire and mixed with a little oil; then after this he should bring the wax to a sweat by warming it and the wall at close quarters with charcoal enclosed in an iron vessel; and finally he should smooth it all off by rubbing it down with a wax candle and clean linen cloths, just as naked marble statues are treated.

4. This process is termed [Greek: ganosis] in Greek. The protecting coat of Pontic wax prevents the light of the moon and the rays of the sun from licking up and drawing the colour out of such polished finis.h.i.+ng.

The manufactories which were once at the mines of the Ephesians have now been transferred to Rome, because this kind of ore was later discovered in Spain. The clods are brought from the mines there, and treated in Rome by public contractors. These manufactories are between the temples of Flora and Quirinus.

5. Cinnabar is adulterated by mixing lime with it. Hence, one will have to proceed as follows, if one wishes to prove that it is unadulterated.

Take an iron plate, put the cinnabar upon it, and lay it on the fire until the plate gets red hot. When the glowing heat makes the colour change and turn black, remove the plate from the fire, and if the cinnabar when cooled returns to its former colour, it will be proved to be unadulterated; but if it keeps the black colour, it will show that it has been adulterated.

6. I have now said all that I could think of about cinnabar. Malachite green is brought from Macedonia, and is dug up in the neighbourhood of copper mines. The names Armenian blue and India ink show in what places these substances are found.

CHAPTER X

ARTIFICIAL COLOURS. BLACK

1. I shall now pa.s.s to those substances which by artificial treatment are made to change their composition, and to take on the properties of colours; and first I shall treat of black, the use of which is indispensable in many works, in order that the fixed technical methods for the preparation of that compound may be known.

2. A place is built like a Laconic.u.m, and nicely finished in marble, smoothly polished. In front of it, a small furnace is constructed with vents into the Laconic.u.m, and with a stokehole that can be very carefully closed to prevent the flames from escaping and being wasted.

Resin is placed in the furnace. The force of the fire in burning it compels it to give out soot into the Laconic.u.m through the vents, and the soot sticks to the walls and the curved vaulting. It is gathered from them, and some of it is mixed and worked with gum for use as writing ink, while the rest is mixed with size, and used on walls by fresco painters.

3. But if these facilities are not at hand, we must meet the exigency as follows, so that the work may not be hindered by tedious delay. Burn shavings and splinters of pitch pine, and when they turn to charcoal, put them out, and pound them in a mortar with size. This will make a pretty black for fresco painting.

4. Again, if the lees of wine are dried and roasted in an oven, and then ground up with size and applied to a wall, the result will be a colour even more delightful than ordinary black; and the better the wine of which it is made, the better imitation it will give, not only of the colour of ordinary black, but even of that of India ink.

CHAPTER XI

BLUE. BURNT OCHRE

1. Methods of making blue were first discovered in Alexandria, and afterwards Vestorius set up the making of it at Puzzuoli. The method of obtaining it from the substances of which it has been found to consist, is strange enough. Sand and the flowers of natron are brayed together so finely that the product is like meal, and copper is grated by means of coa.r.s.e files over the mixture, like sawdust, to form a conglomerate.

Then it is made into b.a.l.l.s by rolling it in the hands and thus bound together for drying. The dry b.a.l.l.s are put in an earthern jar, and the jars in an oven. As soon as the copper and the sand grow hot and unite under the intensity of the fire, they mutually receive each other's sweat, relinquis.h.i.+ng their peculiar qualities, and having lost their properties through the intensity of the fire, they are reduced to a blue colour.

2. Burnt ochre, which is very serviceable in stucco work, is made as follows. A clod of good yellow ochre is heated to a glow on a fire. It is then quenched in vinegar, and the result is a purple colour.

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