This is used to test the bonding strength of "paint to wood" and "paint to paint" (inter-coat adhesion) to determine whether an existing film is sound or requires removal.
Using a sharp utility knife, score 4 parallel lines 3/16" apart. Score 4 additional lines in the same manner perpendicular to the first, creating a tick-tack-toe. Scoring should go through all layers of the paint film and into the wood substrate.
Using a piece of clear cellophane tape, test the adhesion by removing the tape quickly. If no pieces of paint are removed, the adhesion of the existing paint film is sufficient to accept additional layers of paint. If some or all of the paint is removed by the tape, the adhesion of the existing paint film is in question and should be removed entirely.