multipositive

A multipositive is a composite film assembly holding multiple positive images arranged on a single base, ready for exposure onto a lithographic plate or resist layer. In offset lithography and photomechanical work, it allows a pressman to burn several design elements, product images, or text blocks onto the printing plate simultaneously rather than exposing them one at a time. The images sit side by side or in grid formation on the film, separated by clear areas that will not transfer ink.

Multipositives are typically assembled by the prepress department using light tables and registration pins to align individual film positives cut from original artworks or film negatives. Each positive film, usually prepared on polyester base material, is positioned and taped or adhered to a carrier sheet. The assembly must hold perfect registration, since any slippage during plate exposure will result in misalignment of colors or elements on the final print. Modern multipositives often use punched pins and pin bars to guarantee alignment across multiple layers when color separations are involved.

A typical multipositive might contain six to twelve images arranged to match the press sheet layout. A job running 10,000 copies at 8-up (eight product images per press sheet) would require precisely the same multipositive for every plate made, making registration setup critical. The size of the multipositive assembly is limited by the largest lithographic plate the equipment can expose, usually up to 40 inches by 50 inches in larger commercial shops.

Errors in a multipositive become expensive: a misaligned image means either scrapping the plate or running the job out of register. Common problems include scratched or wrinkled film, dust particles that block light during exposure, and creep in film dimensions caused by humidity swings in the prepress room. Many shops maintained humidity-controlled darkrooms specifically to keep film positives dimensionally stable.

The term multipositive distinguishes this assembly from a single-positive film or from the assembled press form itself. Once digital workflows replaced photomechanical stripping in most commercial shops, the traditional multipositive became less common, though the method persists in flexography and certain specialty printing processes where film positives remain part of standard workflow.