It is an interesting story on how the offset or lithographic process was invented. Back in 1789 a law student at the University of Ingolstadt in Bavaria, Germany, wrote a play entitled "Die Maedchenkenner" and had it published. After printing costs were subtracted, he made a sizable profit and was now convinced his fortune was to be made on the stage. Alois Senefelder is little known to us today as a playwright, but is recognized as the inventor of lithography.

The play, Die Maedchenkenner, Herr Senefelder wrote was successful. His following plays, however, were not well received and he lost money on all of them. He became convinced, however, that it was not the quality of writing but rather the high cost of printing that caused his financial strain. After viewing the printer in action, he decided the art of printing was a simple task and resolved to learn the craft so that he could not only write but print his own works.

At this time in the area of Bavaria, the most common method of printing was copperplate engraving. The images to be printed were carved in reverse into soft copper plates with a flexible steel tool. Senefelder purchased the necessary tools and materials and began to learn the printer's craft. He soon learned that this new craft he was undertaking was not as easy to learn as it looked. He made many errors in engraving the copper and finally had to invent a correction fluid to correct his mistakes.

Unfortunately, even with his correction fluid, Herr Senefelder's skills and finances were so limited that he could not afford to continue practicing on real copper plates. He tried other materials to no avail.

During his search for another plate material, he happened upon a material called kellhein stone, which was a limestone quarried at a local site. This stone possessed a unique quality that slabs of nearly any thickness could be easily cut and unlike copper, could be polished to a perfect surface with little effort.

Senefelder practiced writing in reverse on the newly found stone to develop the skill necessary to be able to return to copper. In his book Senefelder wrote:

"I had just succeeded in my little laboratory in polishing a stone plate, which I intended to cover with etching ground, in order to continue my exercises in writing backwards, when my mother entered the room, and desired me to write her a bill for the washerwoman, who was waiting for the linen. I happened not to have even the smallest slip of paper at hand, as my little stock of paper had been entirely exhausted by taking proof impressions from the stones nor was there even a drop of ink in the inkstand. As the matter would not admit the delay, and we had nobody in the house to send for a supply of the deficient materials, I resolved to write the list with my ink prepared with wax, soap and lampblack, on the stone which I had just polished, and from which I could copy it at leisure." (Alois Senefelder, A Complete Course of Lithography - 1819 edition)

From that experience Senefelder got an idea. Making a border of wax around the stone, he allowed an acid solution to stand on the entire stone surface for a short period of time. The limestone was etched away in any areas on which he had not drawn an image. The wax writing solution resisted the acid. After he removed the acid, he found that the coated, or image, areas were raised about 1/10 inch above the rest of the stone. By carefully rolling ink over the surface, he could ink only the image and easily transfer this ink to a sheet of paper with a little pressure.

This method was still not what we today consider "Lithography" as Senefelder was printing in relief. Because of the low cost of the stone, Senefelder felt he could easily sell the technology to local printers for jobs. He began to experiment with his invention immediately. Senefelder called his invention "lithography," based on the Greek words Lithos, meaning stone, and graphein, meaning to write, hence, stonewriting.

While this method of printing was a significant advancement over the older copperplate system, his greatest contribution was the refinement of what he called "chemical lithography." After several years of experimentation, Senefelder observed that a solution of "gum" (arabic gum and water), when coated over the stone, would clog the pores in the stone and would repel ink. As long as the gumwater mixture remained moist, an ink brayer rolled over the entire stone surface would deposit pigment only in the image areas on the stone. By alternately moistening and inking the stone, he could build up a layer of pigment sufficient to transfer a perfect image to a sheet of paper.

It is this concept of moisture and ink repelling each other that is the basis for all contemporary lithographic printing. Today this concept has been modified such that the ink is made to pickup as much as 50% of the gum-water (fountain solution) mixture.

As time and experimenting progressed, Senefelder found that the gum-water mixture worked best under acidic conditions, in the pH range between approximately 3.5 and 5.0. The gum arabic was not as effective outside this pH range and ink would begin transferring to the non-image areas. During the printing process, contaminates would enter into the gum-water mixture raising or lowering the pH to a point where the gum was no longer effective in protecting the non-image areas from ink.

To combat this, buffering agents were added to the gum-water mixture to keep the pH stable as contaminates were introduced to the mixture. As lithographic plate technology progressed, acids were also added, such as phosphoric acid, to help clean the offset plate by very slightly etching the non-image areas during each revolution of the printing press. Other additives are added today such as cleaners, lubricants, wetting agents, etc.