Complete Works, Vol. V

are generated from one and the same cause; for it is made from watery transparent material with strongly burnt earth; and according to whether this is clearer or less clear, that greenness also becomes clearer or less clear. A sign of this is in glass that is made from a mixture of lead; for this is very green, and is made purer the more often and more it is burned. For in repeated burning, the transparent is purified and thinned, and the clarity of fiery light is more infused into the nature of the water; and therefore it is clarified. The intermediate color, which is like tawny and azure, as is in the stone that is called cornelian, is caused by a terminated transparent [substance] which is similarly superimposed with thick, smoky, watery, and ignited earth. And these are almost all the colors that are found in precious stones. After the one that is like onyx, and the sparkling snow-white, by which the stone called the orphan a legendary precious stone of unique value, often associated with imperial crowns is said to be colored. For the onyx or onychine stone is composed of a substance that is of double color, and it is found sometimes with more colors than two, but as frequently it is composed of a double color, one of which floats above the other. The lower one is indeed like flesh-colored, which is from earthy material that is highly smoky and mixed vaporously. The upper one, however, is somewhat pale and slightly dusky, and this is caused by the victory of the transparent over the opaque in the mixed parts; so, however, that the opaque is altering the white. It is of such a substance when watery material mixed with a little subtle earth evaporates, and in evaporating, it coagulates into stone. One finds onychines having very red veins and very white ones, the causes of whose colors it is not difficult to find from the aforementioned. But the sparkling snow-white is undoubtedly caused by the fact that it is mixed from a transparent body that is, as it were, solidified; for the dust of any transparent thing is found to be very white; and when the dust is continued, a white, glistening body results, like a pearl; which happens from the striking of light

to the surfaces of polished parts; for which reason the stone is said to shine somewhat in darkness like a glow-worm. For in the day, the light that is incorporated into the diaphanous part of the stone is covered due to the greater light, but in the night it shines; and therefore in the day that white stone is seen like a glow-worm. The perfect theory of all these must be delivered in the science of the generation of sensibles. A stone of many very different colors is also found; for which reason it is called panther, all the colors of which are caused by the diverse substances from which the parts are composed; for the same theory applies to the whole and the part regarding the tincture of the body. So many and so much have been said regarding the science of the color that is found in precious stones. Amethyst follows the ruby in obscure transparency. And chalcedony follows beryl in a substance that is as if transparent, yellow, and foul-smelling, just as lead imitates silver.

CHAPTER III.

These stones that are found to be of transparent and non-terminated substance are of very many colors, and they are of four kinds, as it is common to say, namely: flints, tufa, square stone a type of building stone/freestone, and marble. In all these kinds, many colors are found, namely black, sea-green, slightly green, and white. Outside the genus of marbles, there is hardly a large red stone, but small red ones are found, especially in the kinds of marble. And for all kinds of colors, the theory is the same as that which was said in the preceding; but this happens to kinds of marbles, that the parts drawn from them