US27981A - James matuison - Google Patents

Description

UNITED STATES PATENT OFFICE.

A. HOEN, OF BALTIMORE, MARYLAND.

COMPOSITION FOR ETCHlNG STONE.

Specification forming part of Letters Patent No. 27,981, dated April 24, 1860.

To all whom it may concern.-

Be it known that I, A. HOEN, of Baltimore, in the county of Baltimore and State of Maryland, have invented a new and Improved Gomposition for Etching Stone; and I do hereby declare that the following is a full, clear, and

exact description of the same.

The ordinary method of etching stone is attended with many serious difficulties, which make it impossible to produce a perfect picture. After the stone has been prepared it is covered with an etching-ground capable of resisting the acid to be used, (generally nitric acid or hydrochloric acid.) The design to be produced is now worked into this ground with a fine-pointed needle, the burin or graver, parallel lines being drawn with the ruling-machine and diamond for skies, tints, &c. The lines thus produced are all of the same size, without regard to any light or shade, and a plate thus prepared has therefore no effect whatever. To produce such the lines have to be etched in with nitric or hydrochloric acid, iainter or deeper, according to thelight or shade of the picture. For this purpose a weak solution of the acid is poured over the whole surface of the stone, and after remaining a certain time washed off with clean water and dried, and those parts which in the opinion of the artist are etched deep enough are stopped out with lithographic ink to prevent a further action of the acid. The acid is now poured over the stone again and left standing long enough to produce the second tints, when the surface is washed and dried, as above described. The second tints are now stopped up, and the same process is repeated until the several shades of the picture are produced. The most serious defect of this process is found in the fact that the artist can never know with certainty the depth of the lines, and he can only guess it by the strength of the acid, by the time it remains on the stone, and by the nature and chemical composition of the stone itself. Another difficulty is caused by the continual stopping out of the finished parts, which completely prevents the artist from seeing the progress of his picture. His memory is his only guide, and this is very apt to confuse and mislead him. Furthermore, the gradation from one tint to the other will always be more or less visible, showing by decided marks the previous covering with ink. All these diliiculties are avoided by the use of my composition for producing the picture.

I prepare the stone and cover its surface with etching-ground in the usual manner. The design is now worked into the etching-ground and the stone is ready t6 be acted on by the acid, as previously described; but, instead of using nitric or hydrochloric acid for a mordant I use some acid which forms an insoluble combination with the lime of the lithographic stone-such as citric acid-which, after being washed off with water, leaves a very small quantity of a white powder-via, citrate of lime--in the lines, which enables the artist to judge accurately of their respective strength by the contrast they form with the dark covering of the stone. Such acid, however, when used alone, will spread and run to those parts which it is not desired to touch, and in order to give to said acids a certain consistency I mix them with gum-arabic, whereby the artist is enabled to use a camels-hair brush and to put on the acid in the same manner as if he were making an india-ink drawing. Light and shade are thus produced with equal facility and in the same manner as with the engravers tool on copper plates previously etched, no stopping out being required until the picture is finished.

The use of gum-arabic in combination with nitric or hydrochloric acid has been found impracticable, as it would prevent the lines from taking the printing-ink--a fact well known to every lithographer. On the other hand, when citric or some other acid having a similar action on the stone is used the small strata of insoluble lime left in the lines prevents the gum from sticking to the surface of the stone, and is therefore no obstacle to the lines taking ink.

The pictures taken from stones prepared according to my method bear a close resemblance to pictures taken from copper or steel plates, and at the same time a great many more impressions can be taken from the stone than from the copper or steel plate, and the printin g is attended with less difficulties.

Having thus fully described my invention,

what I claim as new, and desire to secure by in the manner specified, so as to produce what Letters Patent, is I term the lithokaustik method of etching The employment, as a mordant for lithostone. graphic stones, of a composition ofgum-arabic, A. HOEN. or its equivalent, with citric acid or some other Witnesses: acid, forming a combination insoluble in wa JAMES MATHISON, ter, with the lime of the stone, substantially W. WATKINS.