Abstract The absorption spectrum of ebonite has some practical interest, because the absorption of light causes the surface to deteriorate. A knowledge of the absorption spectrum should help in discovering which are the harmful rays. Published information hitherto appears to be limited to radiation of long wave length, i.e., thermal or infrared. The present note describes experiments on rubber-sulfur (65:35 or 68:32) compositions vulcanized for about 5 hours at 155° C. Owing to the great opacity of ebonite, it is necessary to work with very thin specimens. Various methods of obtaining these suggest themselves: (1) grinding down a small thin sheet; (2) cutting thin shavings; (3) vulcanizing as of a thin film between glass or quartz plates; (4) vulcanizing a film of rubber, deposited on glass or quartz, by immersion in molten sulfur; (5) vulcanizing a deposited film of a rubber-sulfur mix by heating in an inert gas. Methods (1), (2) and (5) have so far been found the most satisfactory. In method (2) it is advantageous to soften the material by swelling, e.g., in nitrobenzene; the swelling liquid can then be removed by extraction with a volatile solvent. Methods (1) and (2) have the advantage of enabling specimens to be obtained from larger pieces that can be analyzed or submitted to other tests.