Blotter art is an art form printed on perforated sheets of absorbent blotting paper infused with liquid LSD. The delivery method gained popularity following the banning of the hallucinogen LSD in the late 1960s. The use of graphics on blotter sheets originated as an underground art form in the early 1970s, sometimes to help identify the dosage, maker, or batch of LSD.
Images may be of various sizes but sheets are often 7.5-inch (190 mm)-square and perforated into a 30 by 30 grid. Individual pieces, separated along the perforations, were sold as "hits", with a carefully calculated dosage in micrograms, so users could plan the intensity of their "trip". Blotter art also appears on blotter paper carrying other potent substances, and on undipped (drug-free) sheets.
Blotter art frequently incorporates themes common to psychedelic art, using bright, contrasting colors and repeating patterns in its designs. Cartoon characters were often exhibited, and many examples contain religious and mystical imagery or pay homage to figures in the psychedelia subculture.
Blotter art has been exhibited at art galleries and undipped blotter is often sold online. San Francisco collector Mark McCloud founded the Institute of Illegal Images, which includes over 33,000 sheets of blotter art.