It will be advisable for the artist, when first etching on steel plate, to keep a register of the time which he finds necessary for the menstruums to act before the parts have attained their clue degrees of strength, and this will serve as a guide to him in his subse quent operations. Mr. Warren generally found about two minutes sufficient for an outline, unless it was required to be very strong; the middle tint was pro duced in about ten minutes, and the darkest shadows in forty minutes. The menstruums should not be more than one-sixth of an inch deep on the plate, otherwise it will be difficult to see the work, and it becomes exhausted in about ten minutes, and thus requires to be replaced. 'While the menstruum is acting, the work must be constantly swept with a cattel-h sir brush, in order to remove the precipi tated copper, which, if allowed to remain in the lines; renders their edges rugged, and destroys their beauty, especial care must be taken to clear the ends of the lines, as they are most liable to bite foul. In stopping out the ground (Brunswick blacks) must be laid on very thin and even, and, instead of terminating ab ruptly, most be re-washed off very gradually; for the smallest ridge or prominence will retain the copper, and then the ground will infallibly be penetrated, and the biting will become foul. By attending to these directions, an etching may be obtained on decar bonized steel, as deep and quite as sharp as it can be on copper. Concerning the great superiority of steel-plate over copper-plate, for all works that re quire a considerable number of impressions to be taken, there can exist no doubt; for though the use of the graver, and of the other tools, requires more time on steel than on copper, and though the process of re-biting has not yet carried to the degree of perfection in the former that it has been in the latter, yet the texture of steel is such as to admit of more delicate work than copper; and the finest and most elaborate exertions of the art, which on copper would soon wear so as to reduce them to an indistinct smeary tint, appear to undergo scarcely any deterio ration on steel; even the marks of the burnisher are still distinguishable after several thousand impres sions.
The improvements on the art of engraving upon steel made by Messrs. Perkins, Fairman, and Heath, are of such a nature as to give them almost the cha racter of the first inventors of the art. The following is their process of multiplying engravings, etchings, or engine work. The steel blocks or plates which are to receive the intended engraving, have their sur faces softened or decarbonized, and thus rendered more suitable for receiving all kinds of work than on copper. When the engraving upon the block has been executed, the plate is completely hardened by a new process which does not injure in the slightest degree the most delicate work. A cylinder of steel previously softened is then placed in the transferring press, and repeatedly passed over the engraved block, by which the engraving is transferred in relief to the circumference of the cylinder; the press having a vi brating motion equalling that of the cylinder upon its circumference, by which new surfaces of the cylinder are presented equal to the extent of the engraving.
This cylinder is then hardened, and is employed to indent copper or steel plates with engravings identi cally the same as the one on the original steel block, and this may be repeated ad infinitunt, as the original engraving will remain, from which other cylinders may be impressed if required. When the engraving is of too great a size to be transferred, it is executed upon a steel block, from which when hardened, 200,000 perfect impressions may be taken.
In our pottery manufactures, in calico-printing, but particularly in preventing the forgery of bank notes, Sze., this art will be found of the greatest im portance.
We have already seen that Mr. Warren experienced difficulties in obtaining a good menstruum for biting in upon steel. Mr. Wilson Lowry discovered a men struum, the composition of which he sold to Mr. Heath, by which the lines could be bitten in deep as well as broad, and the requisite fineness preserved. It is well known that some menst•ua succeed well on hard steel, and yet give unsatisfactory results on soft and decarbonized steel. Nitric acid; which is the ac tive ingredient in all these menstrua, usually reduces part of the iron to the state of that oxide which is soluble in the acid, and also converts a smaller portion to the state of peroxide which remains for the most part undissolved, adhering to the surface of the iron, and preventing that clean, deep, and uniform biting which it is the great object of the artist to obtain. The presence of carbon in a finely divided state has a tendency to interfere with the peroxidation of the iron, and this probably is the reason why it is less dif ficult to obtain a good effect with hard than with soft steel.* Hence it became of to have a men struum by which these effects would not be produced, and this seems to have been obtained by Mr.Hum &treys. who was rewarded by the society of arts for the discovery of the following menstruum.
Dissolve together hi half a pint of hot water a quarter of an ounce of corrosive sublimate; and a quarter of an ounce of powdered alum. It is ready for use when cold. " While using it keep it stirring with a camel's hair brush, and take care to wash the plate perfectly after each boiling. As this acid, though clear before use, becomes turbid during its ac tion on the steel, it may be prudent in fine works to throw away each portion of acid after it has been on the plate. The taste and experience of the artist must dictate the length of time he may leave it on his plate; delicate tints are obtained in about three minutes." For farther information on this subject, see The Transactions of the Society of ..arts for 1823, vol. xli. p. SS; and Newton's Journal of the _Oils, vol. xiii. p. 12.
On an improved mode of etching. Steel Plates. By Mr. W. COOKE, Jun., Engraver.
From the Transactions of the Society for the encouragement of Arts, Manufactures, and Commerce.