IRIDESCENT GLASS. - Ancient glass, which has for ages been submitted to the slow disintegrating influence of the damp of the earth and other gently operating agencies, in many instances displays an iridescent play of colours of a most magnificent description. The iridescence thus shown, it has been long known, is due to a process of decomposition resulting in the formation of excessively thin scales of glass. Numerous attempts have been made to imitate by artificial means the gorgeous display of colours thus produced by the slowly acting influences of many centuries, and a certain amount of success has attended some of these efforts. The Venetian glass workers possess the means of giving the surface of their glass a kind of metallic iridescence; and in certain Hungarian glass houses iridescent glass has been made for at least about 20 years. But in 1873, at the Vienna Exhibition, iridescent glass formed a prominent feature, and since that time it has become very common. The iridescent glass now generally seen is a plain flint glass having a slightly metallic tinge and a play of colours like a soap bubble. It is probable that several methods of producing iridescence in glass are practised, as the nacreous lustre in different examples varies considerably. The sulfje-t was investigated by DIM. Fremv and Clemandot ; and under a patent obtained by the latter gentleman, one method, commonly practised, has been made public. It consists in submitting the object to be iridized to the influence of a weak acid solution - such as water with 15 per cent. of hydrochloric acid - under the combined influence of heat and pressure. The effect certainly falls immensely short of the iridescence of ancient glass, but the glass assumes permanently a pearly iridescence, and, though the effect is tiresome, the process will doubtless continue to occupy a place among the methods of ornamenting table glass, ko.