These distinctions of tone and colour which I have ventured to point out are by no means universal, so that a piece which does not possess them must not be rejected as spurious _merely on this account_. Sometimes it is impossible to say from what county a piece came, and this has led experts to refer to the products supposed to emanate from the Cork or Waterford factories as "Munster glass." Even this term is not broad enough, however, for it fails to include the pieces turned out by the Dublin factories, and these are nearly as likely to be mistaken for Cork or Waterford wares, as the two latter are likely to be mistaken for each other. _The blue-grey tinge popularly regarded as exclusively associated with Waterford glass is quite an erroneous means of identification, as most of the pieces I have come across, actually impressed with the mark "Cork Glass Co.," were of this tint._ Dublin glass, before 1800, was very dark in colour, and the very early pieces are almost black. It is very frequently suggested that the chemical action of the air on old Irish glass may have something to do with the mystery of its unique coloration; and, strange as it may seem, it is an undoubted fact that glass does change its tone with the slow lapse of years. I believe this to be specially so with Irish glass which has remained a long time in Ireland; and the existence of such phenomena is borne out by the effect that the atmosphere of Ireland has on old white marble. It may be argued that, should this be the case, the coloration of Irish glass may be caused entirely by the atmospheric conditions under which it is kept, and owe nothing to its local peculiarities of manufacture. This theory, however, cannot be substantiated, _as English glass does not appear to be affected by Irish atmosphere to anything like the same degree as the native metal_. I have frequently seen old Irish dessert services and chandeliers in which individual pieces which had been broken had been replaced by facsimiles made in England. These replaced pieces, however early their origin, do not appear to have changed colour in the least, and because of this can be readily singled out among their fellows of native manufacture. RESILIENCE OF IRISH GLASS.