On Architecture

4. This process is termed ga/nwsis 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 finishing. 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.

1. I SHALL now pass 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 Laconicum, and nicely finished in marble, smoothly polished. In front of it, a small furnace is constructed with vents into the Laconicum, 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 Laconicum 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.

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 coarse files over the mixture, like sawdust, to form a conglomerate. Then it is made into balls by rolling it in the hands and thus bound together for drying. The dry balls are put in an earthern jar, and the jars in

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.

1. IT is now in place to describe the preparation of white lead and of verdigris, which with us is called “aeruca.” In Rhodes they put shavings in jars, pour vinegar over them, and lay pieces of lead on the shavings; then they cover the jars with lids to prevent evaporation. After a definite time they open them, and find that the pieces of lead have become white lead. In the same way they put in plates of copper and make verdigris, which is called “aeruca.”

2. White lead on being heated in an oven changes its colour on the fire, and becomes sandarach. This was discovered as the result of an accidental fire. It is much more serviceable than the natural sandarach dug up in mines.

1. I SHALL now begin to speak of purple, which exceeds all the colours that have so far been mentioned both in costliness and in the superiority of its delightful effect. It is obtained from a marine shellfish, from which is made the purple dye, which is as wonderful to the careful observer as anything else in nature;

2. That which is found in Pontus and Gaul is black, because those countries are nearest to the north. As one passes on from north to west, it is found of a bluish shade. Due east and west, what is found is of a violet shade. That which is obtained in southern countries is naturally red in quality, and therefore this is found in the island of Rhodes and in other such countries that are nearest to the course of the sun.

3. After the shellfish have been gathered, they are broken up with iron tools, the blows of which drive out the purple fluid like a flood of tears, and then it is prepared by braying it in mortars. It is called “ostrum” because it is taken from the shells of marine shellfish. On account of its saltness, it soon dries up unless it has honey poured over it.