Of course, all these things being distinctive are imitable, and here the peril of the collector begins. The expert is rarely deceived as to whether any specimen is genuine old glass; but so pervasive and so perfect are the imitations that exist, and so plausible the conditions under which they are found, that it behoves the amateur to use the extremest caution. I propose to deal at some length with some of the more obvious and frequent frauds and fakes in a subsequent chapter. But for the moment it may be said that the best test of genuineness is neither shape nor any particular design--for these can be closely imitated--but the colour. There is a curious tint in old glass which the new never quite achieves. The would-be small collector will be well advised if, before riding his hobby, he goes through a brief course of eye-training under the guidance of an expert, until he gets the exact tone of the old glass firmly impressed upon his memory. As an additional factor, it should always be borne in mind that the old glass is invariably heavier than its modern imitation. It will be desirable at this point to describe in brief detail the more important of the types of eighteenth-century glass enumerated on page 59. _Glasses with Incised and Ribbon-twisted Stems._--The incised or ribbon-twisted stemmed glass [Illustration: Tear Glasses FIG. 41.] as shown in Fig. 36, is usually about 6 inches high with, generally, a flanged or outward curved top and a comparatively slender stem. A series of ribs was impressed by a mould on the stem whilst yet plastic. The stem was fixed to its bowl, heated till soft, and then gently twisted and, at the same time, stretched. The result was a twist, produced in exactly the same way as in a stick of candy--close at the top and gradually loosening toward the bottom. Near the foot, by the way, the spiral generally disappears entirely as the effect of the heating process necessary when the foot was joined to the stem. The bowl was almost invariably waisted, that is, its sides were bent inwards. The foot was folded and there was a characteristic lessening in the diameter of the stem as it neared the bottom, which the “puller” of toffee will readily understand. _Air-twisted Stems._--The air-twist probably began with a “tear.” The tear of the glass-blower is a bubble of air blown into the centre of a mass of molten glass, possibly at first by accident and afterwards by design, as a form of ornamentation. When the stem was [Illustration: FIG. 7--AIR-TWIST STEMS. (From the Rees Price Collection, by permission of the Connoisseur).]