Part 9 (1/2)

APPENDIX

(1) Printing simultaneously with water colors and oil colors.

(2) Simultaneous chemical and mechanical printing.

(3) Application of the stone for cotton-printing through wiping--a unique printing method.

(4) Color print through wiping.

(5) Oil painting print through transfers.

(6) Stone-paper.

(7) Applying the chemical printing process to metal plates, etc.

INTRODUCTION

Printing from stone is a branch of a new process, different in fundamental principle from all others, namely, the chemical process.

Heretofore there have been two leading printing processes for manifolding writings and drawings, one working with characters in relief, the other with sunken characters.

Of the first kind is the ordinary book-printing, in which the characters are made of metal or wood in such form that only those lines and points are elevated that are to take color, everything else being depressed.

The wooden forms for cotton-printing are made thus also.

Of the second kind are all copper and zinc plates, and the cotton-print process with copper plates or cylinders. In this method the lines and points to be printed are depressed, being either engraved, etched, or stamped.

As is well known, the first method of printing is as follows: The letters, which are all at the same elevation and, therefore, furnish a plane surface, are inked with a leather ball, stuffed with horsehair.

As the ball is so firm and elastic that it can touch only the elevated parts, these alone can take the color, which adheres because of its sticky nature. The same is true of the carved wood used in cotton-printing, with only the difference that, instead of rubbing with a leather ball, the wooden plate itself is laid on a cus.h.i.+on covered with the color, and then, being placed face down on the cloth, is hammered gently to produce the imprint.

In copper and zinc printing the method is reversed. In order to force the color into the depressed parts, which alone are to be printed, the entire plate is coated with color, and then the elevated surface is cleansed again carefully. The cleaning rag cannot reach the depressed grooves, so that more or less color adheres to these according to their various depths. Under the powerful press, which forces the paper into all the engraved parts, this color transfers itself and thus gives the desired impression.

It is evident that both methods rest on purely mechanical principles: book-printing being based on the fact that the color adheres only on those places that it can reach, and copper-plate printing depending on the fact that the color remains only in those places from which it cannot be removed by cleansing.

It is different with the chemical print. This does not depend on either elevation or depression of the design. It depends on the fact that the design is coated with a preparation of such nature that afterward the printing color, which is made from a related substance, adheres because of its chemical similarity; and furthermore, because all parts of the plate that are to remain white, have been so treated that they repel the color. These two purely chemical objects are attained fully with the new process. Daily experience proves that all fatty bodies, such as oil, b.u.t.ter, tallow, fish oils, etc., and all such as easily dissolve in oil, like wax, resin, etc., refuse to unite with any watery substance without the aid of some third body that will bring about such union. The chief solvent for this purpose is alkali, which, under proper manipulation, always produces a sort of soap that then is soluble in water. Sometimes, to be sure, an apparent union can be produced by violent shaking or mixing, without the use of the alkali, but at the first opportunity the fatty substances separate themselves again from the watery ones.

It is on this fact that the entire method of the new process is based.

It is termed chemical printing with perfect propriety, as the reason why a fatty color, say, linseed oil varnish, will adhere only on the designed parts of the plate and is repelled by the rest of the surface, is due to the chemical properties of the materials.

It might be maintained that in the other forms of printing, color adheres from the same reason. This is true, to be sure; for it is a general law that water and oil will adhere to all bodies that are dry.

But it is not the case with these fluids mutually; and in this fact lies the unique difference between the older and the new processes. A dry plate would take color over its entire surface. If, however, it is dampened, it will take oil color only on those places that are in a condition opposite to dampness. Therefore, the repelling of the color from those parts that are to remain white is the novelty.

It must not be imagined, however, that to print chemically it suffices to dampen certain parts of the plate and to coat others with fatty substance. With most of the materials available for printing, mere water does not suffice to produce a sufficiently repelling obstacle between the plate and the color.

With flinty and clayey bodies,--for example, gla.s.s, porcelain, slate, etc.,--one can manage with mere water; but then the slight adherence of the fatty color to the plate produces an opposite difficulty, by preventing any large number of impressions. Still, by using very firm and readily drying fatty substances, such as linseed oil varnish dried with litharge of silver it is possible, in case of need, to succeed fairly well.