Dot Patterns Tell the Story
Chromolithography, or stone lithography first appeared in America in 1840 and was in common use by the end of the Civil War. After the turn of the century, lithography (using four colors and metal printing plates) slowly replaced the more expensive and much more time consuming chromolithography.
Chromolithography relies on the principal that oil and water don't mix. The process employed the use of a polished limestone or zinc plate with an image applied by hand with a oil based crayon. Each color within the image required the use of a different stone with a different image.
After the oil-based image was put on the surface, a solution of gum arabic in water was applied. The gum arabic sticks to the non-oily surface, and is repelled by the oily surface. Then the stone and a sheet of paper are run through the press. During printing, water adhered to the gum arabic surfaces and the colored oily ink stuck to the oil-based image surfaces.
Many early Coca-Cola lithographs use twelve or more colors, and sometimes took several months to produce. Today, we can only imagine the patience and skill these early artisans possessed.
The images below show the printing process as it applies to a 1913 Coca-Cola calendar and a 1910 paper poster.
Notice the somewhat random stippling pattern of the dots on the model's cheek and on the flare glass she is holding. This stippling pattern is representative of the chromolithographic printing process.
When examining what is represented as an early piece of printing, remember to look for this pattern of hand applied stippling.
Note that around the mid-teens some items were beginning to be printed through the use of the new process of photolithography, and then subsequently enhanced with the techniques of chromolithography.
Modern offset photolithography differs from traditional chromolithography in that the image is transferred photographically onto a flexible metal or polyester plate that is covered with a photo sensitive emulsion. The plate is then placed on a rotary printing press. Early on, in the transition from chromolithography to photolithography, stones were still used on traditional flat bed presses.
The image to be printed is screened photographically and broken down into four standard colors (cyan, magenta, yellow and black). It is also broken into a sequence of tiny different sized dots that form a pattern of lights and darks. Each of the four colors uses one plate.
On the rotary printing press, this printing plate then rolls against a cylinder covered with a rubber blanket. The blanket squeezes away the water, picks up the ink and transfers it to the paper. Since the image is first transferred (or "offset") from the printing plate to a rubber blanket, the process is referred to as offset printing.
This more economical form of printing came into common use around the turn of the century, and by 1930 had become the dominant technique for advertising products.
As seen in the images of the 1937 blotter, upon slight magnification the uniform arrangement of the four-color printing dots becomes evident. This uniform arrangement is very obvious when compared to the more random stippling of chromolithography.