Possibly the appearance of the metal and the style of workmanship are as reliable guides as any others. The metal of the earliest glasses was by no means perfect. Instead of the beautiful clarity and perfect transparency we are accustomed to associate with glass, there is often a streakiness or cloudiness visible in the material, together with numerous bubbles and flaws. If the striations are horizontal, the glass is of an earlier type than if they are perpendicular. The sides of the bowl are often irregular, and the stems are often clumsy, uneven, badly balanced, and altogether disproportionate in point of size to an eye accustomed to the slenderer style of modern glassware. An important point is the junction between the bowl and the stem. For some extraordinary reason, the welding of the two seems to have given the ancient glass-blowers considerable trouble, and the join is often too clearly perceptible. Hence the collector who comes across an apparently ancient piece bearing evident signs of clumsy joining should give it more than casual attention. Sometimes, to obviate the difficulty, the base of the bowl was made into a kind of knop, and at other times the junction was hidden by an irregular band—the prototype of the collar which so often appeared in glasses of a somewhat later period.
The bubble which appears in many stems was probably the outcome of accident and possibly of an attempt to imitate the hollow stems of Venetian glass. It is worthy of note that whilst the bubble is almost invariably present in the baser forms of early eighteenth-century glass, it is frequently absent from the finer varieties. Another point of difference is that the better specimens rarely have the folded foot, which is invariably present in the coarser makes, the turning under of the rim, whilst plastic, to make a kind of welt, being an obvious precaution against the rougher usage to which they were inevitably subjected. Sometimes the feet were domed, but these were difficult to make and the numbers were restricted. In some specimens ridges or ribs are formed on the upper and lower sides of the foot.
The earliest glasses were devoid of any attempt at decorative engraving, and these plain glasses may also be roughly classified by noting whether the glass rests on the flat of the foot or on the rim only. The former are of the earlier type.
Among the tests which the collector might apply are the following:—
Note whether the glass rings clear and sweet in tone. In twisted stems, note whether the stem twists to the left or the right. The genuine glasses have almost invariably stems twisted to the left. In opaque-twisted stems, note particularly the colour of the spiral. In the forgeries the opacity is less definite, the twist often having a kind of translucent look.
Genuine old glass often has a cloudy tinge with frequently a tone of steely blue. Forgeries may show a greenish tint.
In old glass the centre of the base, where the piece was, after being finished, knocked off the pontil, is generally left rough; in the imitations it is generally ground smooth.
The foot of a genuine old glass is never quite flat, there is always a slope—sometimes a very pronounced one—from the centre to the edge. The modern imitation, usually made abroad, often has a perfectly flat foot.
The edge of the bowl in a genuine old glass is always rounded, never left hard and sharp.