Mixed up with a great deal of fabulous and fantastic matter, this treatise contains instructive and interesting notices of the composition and the colouring of old glass, including that of Spain. One of such notices is the following. "Of the eleventh degree of the sign of Sagittarius is the glass stone, containing a substance which is a body in itself (sand), and another which is added to it (salt), and when they clean these substances and draw them from the fire, they make between the two a single body. The stone thus made (glass) has many colours. Sometimes it is white (and this is nobler and better than the others), or sometimes it is red, or green, or _xade_ (a dark, burnt colour), or purple. It is a stone which readily melteth in the fire, but which, when drawn therefrom, turneth again to its former substance: and if it be drawn from the flame unseasonably, and without cooling it little by little, it snappeth asunder. And it receiveth readily whatever colour be placed upon it. And if an animal be hurt therewith, it openeth as keen a wound as though it were of iron." The treatise also describes a stone called _ecce_, which was used in glassmaking, saying that it was found in Spain, "in a mountain, not of great height, which overlooks the town of Arraca, and is called Secludes. And the stone is of an intense black colour, spotted with yellow drops. It is shiny and porous, brittle, and of light weight ... and if it be ground up with honey, and the glass be smeared with it and submitted to the fire, it dyes the glass of a beautiful gold colour, and makes it stronger than it was before, so that it does not melt so readily, or snap asunder with such ease." I have said that the power of a diamond to cut glass is referred to in the same work, which further tells us that this gem "breaketh all other kind of stones, boring holes in them or cutting them, and no other stone is able to bruise it; nay more, it powdereth all other stones if it be rubbed upon them ... and such as seek to cut or perforate those other stones take portions of a diamond, small and slender and sharp-pointed, and mount them on slips of silver or of copper, and with them make the holes or cuttings they require. Thus do they grave and carve intaglios."