The term "print" is often shorthand for an offset lithographic print, which is the most common type of commercial printing used today, according to John C Berg, Ph.D., a chemical engineer who has researched print media and technology. Offset lithography is premised on the basic principles of oil-and-water repulsion in order to replicate an original in a high-speed press. While the colors often vary from the original, the quality, speed and low cost of offset lithography has secured its popularity. Meanwhile, lithography prints are handmade by an artist who draws directly onto a piece of stone, aluminum or plastic. Then the artist pulls the print onto paper by pouring ink into the design. The latter are generally considered of higher value due to their high quality and low print runs. Distinguish the difference by using a magnifying glass to scrutinize the prints.
Look for the signature of the artist or numbers indicating the print is part of a limited edition at the bottom of the print or on the back of the print. Hand-pulled lithography prints are often signed by the artist, but offset lithography prints will not be signed.
Look closely at prints with a magnifying glass to see if there are any organized rows of colored ink dots. Offset lithography prints will often leave a dotted circular pattern in rows, which emerge during the mechanical color separation process. Meanwhile, random ink dots or discolorations indicate the print is hand drawn.
Examine with a magnifying glass or your naked eye the background areas of each print for discoloration. While an offset lithograph printer produces very high-quality prints, there is a slight chance that if the aluminum printing plates have not been maintained, chemical oxidation will result in markings or blemishes in non-image areas that will be unusual in color as they are neither part of the design nor ink.
Run your finger along the line where ink meets the paper. Feel how thickly the ink is laid on the paper. On a offset lithography print, the ink will not be raised from the paper. But in handmade, wood block, silkscreen or letterpress lithography printing techniques, the ink will be slightly raised. In places where there is more than one color layered, the ink layer will be thick.
If the print is from a reputable art dealer and has the characteristics of a hand-pulled lithography, it is more likely that it is an original lithography and not an offset print.