or Engraving upon, is in the article CHEMISTRY (Encyc.) said to be a new art; and as that acid which dissolves siliceous earth, and also glass, was first discovered in the year 1771 by Scheele, one might naturally imagine that the art of etching with it upon glass could not be older. By many others, as well as by us, it has indeed been noticed as a new invention; yet Professor Beckmann, whose labours have brought many things to light, has proved, that so early as the year 1670 the art of etching upon glass was discovered by Henry Schwanhard, son of George Schwanhard, who was a celebrated glass-cutter, patronized by the Emperor Ferdinand III. about the middle of the last century. At the time of his death, 1667, the father practised his art at Prague and Ratibon. Whether the son followed the same business at the same towns, or removed to Nuremberg, is not very evident from the professor's history; but in the year above-mentioned, some aqua regia (nitro-muriatic acid) having accidentally fallen on his spectacles, he was surprised to find the glass corroded by it, and become quite soft. He thus found himself in possession of a liquid by which he could etch writing and figures upon plates of glass.

Such is our information; but if it be admitted (and it would display unreasonable scepticism to question it), Schwanhard must either have improved the nitro-muriatic acid! acid by some means or other unknown to us, or have confined his etchings to some particular kinds of glass; for the fluoric is the only acid, with which we are acquainted, that corrodes all glasses. (See Chemistry-Index in this Supplement). M. Beckmann indeed seems to think that he had discovered the fluoric acid itself; for in the year 1725 there appeared in a periodical work the following receipt for making a powerful acid, by which figures of every kind can be etched upon glass.

"When the spiritus nitri per distillationem has passed into the recipient, ply it with a strong fire, and when well dephlegmated, pour it, as it corrodes ordinary glass, into a Weldenburg flask. Then throw into it a pulverized green Bohemian emerald, otherwise called heliophorus (which, when reduced to powder, and heated, emits in the dark a green light), and place it in warm sand for 24 hours. Take a piece of glass well cleaned, and freed from all grease by means of a ley; put a border of wax round it, about an inch in height, and cover it all over with the above acid. The longer you let it stand so much the better; and at the end of some time the glass will be corroded, and the figures which have been traced out with sulphur and varnish will appear as if raised above the pane of glass."

That the Bohemian emerald or heliophorus mentioned in this receipt is green sparry fluor, cannot, says the professor, be doubted; and he seems to have as little doubt of the receipt itself having passed from Schwanhard and his scholars to the periodical work of 1725, from which it has been lately inserted in the Cökonomische Encyclopedie of Krunitz. This supposition certainly acquires a considerable degree of probability from the similarity of Schwanhard's method of etching to that which is here recommended, and which is so different from what is now followed. At present, the glass is covered with a varnish either of shining dissolved in water, or of turpentine oil mixed with a little white lead; through which the figures to be etched are traced as on copper; but Schwanhard, when he had drawn his figures, covered them with varnish, and then by his liquid corroded the glass around them. His figures, therefore, when the varnish was removed, remained smooth and clear, appearing raised from a dim or dark ground; and M. Beckmann, who persuaded some ingenious artists to make trial of this ancient method of etching, declares, that such figures have a much better effect than those which are cut into the glass.

Before concluding this article, it may be worth while just to mention a proposal which has been lately made to employ glass instead of copper for throwing off prints in the rolling press. That it is possible to use glass plates of great thickness for this purpose, it would be rash to deny; but the superiority of such plates to those of copper we cannot conceive. If not broken in pieces in the rolling press, they would doubtless last longer; but the expense of them at first would probably be greater, and the engraving on them could not be so fine.