This is a kind of enamelling, practised, ac cording to some writers, as" early as the se venth century, but afterwards lost until Fini-guerra, an eminent goldsmith ot Florence, brought it into great repute in the 15th cen tury. The art is interesting, as it is supposed to have given the first idea of printing from engraved plates. It consists in engraving a subject on gold or silver, and filling the en graved lines with black or very dark-colored enamel. In the general effect of works in ni ello, there is considerable resemblance to da mascening, except that in the latter the en graved lines were filled up with the precious rcetal, while, in the former, a paste or enamel was made use of. This enamel was a com pound of silver, copper, lead, sulphur and bo rax, forming a dark-colored paste, which was carefully worked into all the lines of the engraving, and fused, by heating the plate. It contrasted favorably with the bright sur-I face of the silver chalice or other article so decorated, producing an effect not unlike that of a copper-plate engraving, or ot a daguerre otype. This kind of work, at one period, constituted the favorite means of adorning, not only all kinds of vessels used for sacred purposes, but also sword-hilts, knife-handles, and other articles in which the precious me tals formed the basis to work upon. In the Museum, at Florence is the most valuable specimen of ancient niello now existing, be ing a plate lor a pix executed by Fin;gueria himself in 1452. An interesting specimen is to be seen in the British Museum, consisting of a silver cup mounted in gold, the orna ments being in niello. This long-neglected art has been revived and again brought into notice by a silversmith of Berlin, named Wagner, who has now settled in Paris. A very successful work in niello was sent by the Messrs. Gass, of Regent street, London, to the Great Exhibition. It was a silver gaunt let niello bracelet, designed by D. Maclise, Esq., R. A., descriptive of " The Promised Gift." Artists in niello find it necessary to take proofs of their work as they proceed, and so in ancient times it is stated that the work was examined by filling the lines with a black fatty material, and then pressing a mass of a peculiar kind of clay upon the design so as to obtain an impression. This process so nearly resembled printing, that it is only to be wondered at that the latter art was not earlier discovered. It is said that the im portant secret was at last revealed by a fe male accidentally placing a bundle of damp linen on a niello plate which had been proved in the workshop of Finiguerra, and which happened to be lying with some of the black material still remaining in the lines. The damp linen absorbed the black, and gave a perfect impression of the plate to the aston ishment and delight of Finiguerra, who im mediately instituted a series of experiments which ended in the discovery ot the art.