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
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 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, relinquishing 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.

CHAPTER XII

WHITE LEAD, VERDIGRIS, AND ARTIFICIAL SANDARACH

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.

CHAPTER XIII

PURPLE

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; for it has not the
same shade in all the places where it is found, but is naturally
qualified by the course of the sun.