Dec. 21, 1825.
SIR—As the Society of Arts have given a portion of their attention to the subject of engraving on steel plates, and as many experiments have failed, I feel great pleasure in making the following communica tion public through the medium of the society.
For the best mode of biting-in hitherto published, we are indebted to the great perseverance of Mr. Turrell ; but the difficulty and danger of using his menstruum on a soft ground, or when the varnish is not sufficiently dry, induced me to use the acids in different proportions, and to leave out the alcohol, as the composition was found to act on the ground, causing the whole surface of the plate to be corroded; this has frequently happened.
It is necessary to mention, that all plates for land scape engraving should be made of steel not com pletely decarbonized.
I beg to submit a few preparatory directions pre vious to etching.
The steel should be carefully cleansed (before lay ing the ground) with turpentine only, omitting the whiting which is used in preparing the surface of copper.
The ground should be laid with as little heat as possible, steel needing not so much as copper ; too high a temperature decomposes the ground, and oc casions it to produce small air bubbles, or to evapor ate in a light smoke from the surface of the plate; should this take place, the ground must be re-laid. It is also highly necessary that in etching the point should penetrate the surface of the steel, and the breath not be suffered to condense on the etching, as it will cause the lines to rust, and will prevent the acid from biting well. The plate being ready for biting-in, the process is as follows : mix, by gentle shaking, six parts of acetic acid, and one part of nitric acid.
This mixture, being very rapid in its action, should be taken off the plate at half a minute, and the acid well washed out of the lines with water, drying the plate well, but without the assistance of heat. Stop out the light tints with Brunswick black varnish; and then, for the purpose of washing the oxyd out of the lines, pour on the plate a mixture of six parts of water, and one of nitrous acid, letting it remain two or three seconds; take this off, and immediately re peat the former mixture without washing the plate between, with water. This process should be re
peated for each tint.
The biting-in of a steel plate should be accom plished, if possible, in one day : this observation holds good in regard to other methods of biting, as the lines will sometimes attract oxygen from the at mosphere during the night, which will prevent their biting with the same degree of clearness as the day before.
When the biting is completed, and the ground taken off, with a strong tooth-brush and turpentine, clean out the remaining oxyd from the lines, using the fingers for the light tints ; then rub the surface of the plate, to remove the bur, with the finest emery • paper previously well used on the back of a steel plate to take off its roughness; the more this pa per is used the more valuable it becomes for taking marks of the scraper from dry point tints.
Re-biting is performed by dipping a clean rag in a very dilute nitric acid, and rubbing it over those parts intended to be re-bitten until the surface be comes dull ; clean the plate out as before mentioned, and in laying the ground the dabber should be used but little, as it is likely to take up the ground again; re-bite with a few drops of nitrous acid in four ounces of water, sufficient to make the water taste sharply of the acid.
The whole process for biting, or re-biting, should be performed in a temperature of about sixty degrees, or higher, and certainly not much below that point.
As the time required to bite-in is the principal thing to be observed, all the light tints should be tried every minute after the first biting; but the deeper ones will require a longer time. A little practice will show these remarks (apparently to be important.