A reversible laser marking material is described which is based on a photothermal transformation between a crystalline and amorphous phase of an anthraquinine dye film. It is shown that the material is stable in ambient conditions in either the crystalline or amorphous phase. The transformation from the crystalline to the amorphous phase can be accomplished with a 6.5-mW 50-ns pulse of a 1-, um spot from the 647-nM line of a Kr laser. The reversal occurs with a 0.93-mW pulse applied for 1 ms. The long erasure pulse time is attributed to the long orientation time for clusters of rodlike dye molecules at the recrystallization temperature. © 1987 Optical Society of America.