This was to learn to write out ordinary type letters exactly, but reversed. I planned that as soon as I attained the skill, I would write them with an elastic steel pen on a copper plate covered in ordinary manner with etching surface, etch, and let the copper-plate printers print them. In a few days I had such skill in reverse writing that I attacked the etching on copper bravely. Here, to be sure, I met greater difficulties. Writing on copper over the etching surface was far more difficult than writing on paper. Then the preparation of the plate, the etching, etc., demanded some practice; but all this I hoped to conquer in time. The one thing that troubled me was that I could not correct the errors made during writing. The accessories of copper-plate engravers, especially the so-called cover varnish, were quite unknown to me. I knew no remedy except to paint the faulty places over with molten wax, but the covering generally became so thick that I could not work through it properly and had to leave the corrections for the graving stilus, which, however, I could not handle at the time.
As, however, the proofs were thoroughly satisfactory to me, I labored desperately to overcome the difficulty. During my student years I had attained much chemical knowledge, and I knew that most of the resinous products which withstand acid, as well as the fats, wax, tallow, and so forth, can be dissolved and diluted partly in etheric oils and spirits of wine, and partly in alkalies. My problem was to obtain a thin mass which would permit itself to be spread very thinly in cold condition over the copper etching surface, dry quickly, become sufficiently firm after drying without getting tough, and, above all, be something that would not attack the etching surface. A few trials with spirits of wine and various resinous forms gave no satisfaction. The one experiment that I made with oil of turpentine and wax also failed, presumably because I diluted the mixture more than necessary, which caused it to flow too much and dissolve the etching surface, at which time several well-done parts of the engraving were ruined. Besides, this mixture dried only slowly to the degree necessary for working. Fortunately I made no further experiments with this material, because then I should not have invented stone-printing, as I know now how to make a cover varnish that is quite satisfactory.
I turned, instead, to an experiment with wax and soap, which succeeded beyond all expectations. A mixture of three parts of wax with one part of common tallow soap, melted over the fire, mixed with some fine lampblack, and then dissolved in rainwater, gave me a sort of black ink with which I could correct faulty spots most easily.
Now I needed only practice in order to carry out my project of etching my literary productions in copper. This presented a new difficulty. After I had written on my single little copper plate, etched it, and pulled proofs at the house of a friend who possessed a copper-plate press, I had to spend some hours again laboriously grinding and polishing the plate, a process which also wore away the copper fast.
This led me to practice on zinc, which was easier to scrape and polish. An old zinc plate of my mother's was requisitioned at once, but the results were very unsatisfactory, because the zinc probably was mixed with lead, and I had used only aqua fortis instead of more powerful acid.
I did not continue trials with zinc, because just then I obtained a handsome piece of Kellheimer stone for the purpose of rubbing down my colors on it; and it occurred to me that if I painted this stone plate with my wax ink, it would serve as well for practicing as copper or zinc, with very little labor in grinding and polishing. The experiments succeeded, and though I had not thought originally that the stone itself might be used for printing (the samples I had seen hitherto of this Kellheim limestone were too thin to withstand the pressure exerted in printing), I soon began to believe that it was possible. It was much easier to do good work on the stone than on the copper. I observed also that I needed weaker and much diluted aqua fortis.
A stone mason told me that he could provide me with this sort of limestone in plates from one inch to eight inches thick. Thus I needed not to fear cracking of the stone; and the only thing that I needed to invent, in order to use the stone just like copper, was either a way to give the stone a better polish, or else a tint which would be easier to rub away than the ordinary copper-plate printing-ink. The stone will not take the polish that is demanded with ordinary printer's ink—and perhaps this is the reason why the stone has not been used long before my time as substitute for copper, for I imagine that such attempts must have been made.
I tried all possible kinds of polishing and grinding without attaining my purpose completely. The result was best when I poured a mixture of one part of concentrated oil of vitriol and four or five parts of water over the stone after polishing it. This mixture, which is very sharp, has the property of boiling immediately when poured over the stone, but ceasing instantly, so that one is tempted to believe that the vitriol has sated itself and lost its power. This is not so, however; for the same fluid, placed on an untouched part of the stone, boils again at once. The reason is that a firm skin of gypsum forms at once on the stone, and this remains impervious to the fluid. If now the etching fluid is poured off and the stone is rubbed lightly with a rag, it attains a shining polish. Unfortunately this is so thin and weak that one can make barely fifty impressions without repeating the process, which involves some loss to the drawing. But if one desires to print in the present chemical style, that is, wet, and the stone is polished before the drawing, one can make several thousand imprints, which will be described in the proper place.
All experiments to find a color easy to wipe away showed me that on a stone prepared with oil of vitriol none was better than a light oil varnish with fine Frankfurter black and some tartar. This mixture could be washed off with a weak solution in spring water of potash and common salt. However, it happened often that slight carelessness in washing destroyed designed parts which took color again afterward only after much trouble. Recollection of this occurrence, which I could not understand clearly at the time, led me some years later to the invention of the chemical stone-printing of to-day.
I have told all these things fully in order to prove to the reader that I did not invent stone-printing through lucky accident, but that I arrived at it by a way pointed out by industrious thought. It will be seen that I knew the ink, before I thought of its use on stone. The stone I used at first only to practice writing. The ease of writing on stone lured me then to try to make it available for direct printing. To do this, I had to discover a way to rub away the black as completely from all unetched parts of the stone as the copper-plate printer can do it from his surface, in comparison with which the stone was but slightly smooth.
At this time my further experiments with this etched form of stone-printing were entirely checked by a new, accidental discovery. Until now I had invented little that was new, but simply had applied the copper-plate etching method to stone. But this new discovery founded an entirely new form of printing, which basically became the foundation of all succeeding methods.
Had the stone merely proved available as substitute for copper, I would have returned to copper as soon as I could afford it, despite several advantages of stone, and for the following reasons: first, the necessary weight and thickness of the stones; second, because the printing process was slower than with copper; third, because probably I never would have become sufficiently skilled in the difficult manipulation of washing off; but chiefly, because the necessary spur, the originality of the discovery, would have been lacking, since I remembered that as a child of five or six I had seen a music-printery in Frankfurt or Mainz where the notes were etched in black slate-stone. I had played often with the broken stones, which lay in a heap near our house. Enough, I was not