Chap. 3 Diapasma, Magma; the Mode of Testing Unguents
Those unguents which are known by the name of “diapasma,”753 are composed of dried perfumes. The lees754 of unguents are known by the name of “magma.755” In all these preparations the most powerful perfume is the one that is added the last of all. Unguents keep best in boxes of alabaster,756 and perfumes757 when mixed with oil, which conduces all the more to their durability the thicker it is, such as the oil of almonds, for instance. Unguents, too, improve with age; but the sun is apt to spoil them, for which reason they are usually stowed away in a shady place in vessels of lead. When their goodness is being tested, they are placed on the back of the hand, lest the heat of the palm, which is more fleshy, should have a bad effect upon them.