US227782A - Lithographic process - Google Patents

Description

A. HOEN. Lithograph-i0 Process.

N'.-.221,'1s2. -Pa tent'ed'May18,.1880.

WITNESSES: [I INVENTOR:

ATTORNEYS.

N. PEYERS. FHOTDAJTNOGRAPHER, WASHINGTON. D. C.

UNITED STATES PATENT OFFICE.

AUGUST HOEN, OF BALTIMORE, MARYLAND.

' LITHOGR'APHIC PROCESS.

SPECIFICATION forming part of Letters Patent No. 227,782,-dated May 18, 1880.

Application filed October 17, 1879.

To all whom it may concern:

Be it known that I, AUGUST HOEN, of Baltimore city, State of Maryland, have invented a new and Improved Lithographic Process; and I do hereby declare that; the following is a full, clear, and exact description of the same.

Letters Patent of the United States were granted to me April 24, 1860, for an improvement in lithographic engraving in the nature of a lithocaustic process.

My present invention is an improved lithocaustic process, which consists in the following-described steps, reference being had to ac-' companying drawings, in which-- 7 Figure 1 is a plan view of a fragment of a lithographic stone having lines drawn therein according to my invention. Fig. 2 is a plan View of such stone, showing the appearance of a portion of its-surface after the lines have been etched by an acid and a series of fine pyramidal points produced. Fig. 3 is a crosssection of the stone on line m m, Fig. 2.

In all three figures the spaces between the lines are greatly exaggerated.

A finely-polished lithographic stone, A, is first prepared, in the usual manner, with acid and gum-arabic, to prevent its-taking ink, as practiced for ordinary engraving. After the gum has been Washed off with water and the surface has become dry, the stone is covered With an asphaltum varnish, or, as technically termed, an etching-ground. Parallel lines are now drawn (by a diamond point attached to a ruling-machine) equidistant both longitudinally and transversely of the stone, all over the space in this etching-ground which will be occupied by the design to be engraved, asv shown in Fig. 1. These lines can be drawn more or less close, according to the fineness of the work to be produced; but in any case a very even and fine net-work of rectangular cross-linin g is obtained. These fine lines are then etched with any acid (hydrochloric being most suitable and efiective) deeper and broader, to such an extent that only the very finest points of the original surface of the stone are left untouched.

From the fact that the diamond point has only cut through the asphaltum varnish or etching-ground, merely exposing the stone in these places, the action of the acid on the lines is not only to etch'them deeper, but also to attack them on the sides, eating under the etching-ground to make them broader. By the prolonged action of the acid on these lines in the peculiar manner stated they will gradually assume the form of regular V-s haped grooves, as shown in Figs. 2 and 3. In this manner a most remarkably even and regular grain is imparted to the stone. From the nature of the grooved lines crossing each other, this grain consistsof a number of very small pyramids, all of the same height and of the same width at the base.

The next step in the preparation of the stone is novel and dissimilar from any known method. It consists in covering the surface of the stone and the afore-described etched lines with a solution of gum-arabic, to prevent them-from receiving the ink in the next part of the process.

and after any of the adhering etching-ground has been removed with turpentine, presents a roughened but perfectly clean surface, impervious to fatty matters by virtue of the gum preparation, which has chemically combined with the stone, leaving on its surface only a very thin insoluble coatingof calcic gum matethat is to say, a substance formed by the chemical union of the gummic acid with the calcium of'the stone. The stone is now, for the second time, covered with asphaltum, which fills the etched lines, and is then suffered to become well dried and hardened. After this has taken place the varnished ground is gently rubbed with a flattened piece of 0s sepiae, or any similar substance, for the purpose of removing the etching-ground or asphaltum from the extreme points of the aforementioned small pyramids'. I

It is evident, now, that these very fine points, not being covered by the protecting varnish, are susceptible of being attacked and.

acted upon by an acid for the purpose of cutting them down. From the fact that these points are the 'apexes of the described pyraters.

mids, it is also manifest that they will become broader in a regular ratio the more they are cut down or the nearer their base is approached, from the nature of their formation. The cutting down of these pyramidal projections for the purpose of forming the design is readily accomplished, either by the use of acid, as in the lithocaustic process, or by the employment of tools in the shape of scrapersi. 0., fiat and pointed needles.

Both methods can be advantageously employed in conjunction with each other, the broad and graduated tints being produced by etching, while the articulation of the subject and the definite lines and touches are produced with great accuracy and facility by the proper use of the tools-that is to say, the etching process may be made use of precisely as heretofore commonly practiced, and the effect will be to cut down the pyramidal points on the different parts of the stone where the acid is applied and where it is desired to produce the aforesaid broad or graduated tints. The design can then be perfected or completed by scraping-tools, which are used to reduce the height of the pyramidal points wherever it is desired to increase the shades of the picture; but instead of availing myself of the etching process I may make'use of mechanical means (scrapers) exclusively-that is to say, either of the above means, separately or in conjunction, will accomplish the object. The artistic effects of light and shade are thus produced by a greater or less abrasion of the pyramidal projections, and in the results thus obtained lies one of the improvements herein described.

The execution of the work by the above process offers great advantages to the artist, for while the work is in progress he has the whole of it continually before his eye, and can form a correct judgment of the effect which his engraving will produce, from the circumstance that the dark etching-ground and the greater or less whiteness of the dots, which increase as the projections are cut down, form a strong contrast, and hence an excellent guide to regulate the shading to the exact depth of tint desired.

Besides accomplishing by the last operation the artistic result described, another one of great importance in a technical aspect is gained. It has been stated that the etched lines and the whole face of the stone beforeit came under the artists hands had been prepared in such a manner as to be impervious to fatty matters, and would reject printing-ink. While the artist is working in the design he is obliged to cut to some extent by tool or acid into the stone, thereby removing the insoluble gum preparation and exposing the natural stone, which in those places is again in a fit condition to be impregnated with fatty mat- This maybe accomplished by means of any greasy substance incapable of dissolving the etching-ground by rubbing it over the finished design, which is thereby converted into a condition which enables it to absorb printing-ink and furnish impressions. When this impregnation of the design with fatty matter has been accomplished the whole of it, together with the etching-ground, is washed oil" with turpentine, the stone then appearing perfectly clean; but when a roller charged with lithographic printing-ink is rolled over it, in the same way as in ordinary lithographic printing, the design, which has been impregnated with fatty matter, will attract the ink and will appear with perfect clearness, and thousands of copies can be printed from it.

This superior mode of engraving offers ad-.. vantages for the production of fine pictural effects, surpassing those of any other mode of artistic engraving. It combines in its nature the facility and freedom of execution of the crayon drawing with the delicate softness of the mezzotint and the well-defined distinctness of the stippled steel-plate engraving.

Although this rectangular system of crosslining gives the best results for nearly all kinds of work suitable for this style of engraving, there may be other effects produced by crossin g the lines at different angles. Even parallel lines, without being crossed at all, can in some instances be usefully employed in imitating line engraving. I therefore do not limit myself to the use of any one of these styles for producing the described roughened surface of the stone, but claim as new and useful the employment of these etchedlines for that purpose.

I am aware that machine-rnlin g and etched lines have frequently been used heretofore in lithographic engraving; but in these cases they have always been employed with a view to receive the printing-ink and form a platein which the design was executed in intaglio.

In my improved method the reverse effect is aimed at, as the etched lines do not in the engraving appear as such in black, but as the white spaces, between the dots of which the I Picture is composed. In this method of engravin g, the white, being represented by lines, is sunk considerably below the level of the general surface of the stone; hence the design itself, being produced by the proportionate cutting down of the projections included between the lines, may not inappropriately be described as an engraving in relief.

I do not claim, broadly, the application of a solution of gum-arabic in water to a lithographic stone, it having long been used for incapacitating the clean places of such stone for receiving ink or grease of any kind, this being the preliminary step in the ordinary process of engraving on a polished lithographic stone; and I am also aware such gum solution has been applied to zinc relief-plates to keep the ink from the body of the plate where not needed.

What I claim is- 1. The improved process of lithocaustic engraving, consisting in drawing parallel crossed lines on the etching-ground covering the lithosistin g in roughening the surface of the stone, graphic stone, for the purpose of giving a then filling the depressions thereof witha gum roughened surface of even texture to the stone, solution, so that they shall persistently repel I 5 then applying an acid for the purpose of deepprinters ink, and subsequently working in 5 ening and broadening the lines and producing the design by abrasion, or otherwise reducing pyramidal points, then covering the lines the projections of such surface, substantially with asolution of gum-arabic in water, then as described. rubbing down or otherwise reducing the points to produce the uneven surface required for the AUGUST HOEN' 10 lights and shades of the engraving, substan- Witnesses:

tially as hereinbefore set forth. SoLoN O. KEMON,

2. The process of lithocausticengraving, con.- AMos W. HART.

Images