ALTHOUGH DENTAL PLASTER AND PLASTER OF PARIS ARE THE MOST COMMONLY RECOMMENDED PLASTERS, NEITHER IS AS EFFICIENT AS DENTAL STONE FOR MOULAGE. FIVE PLASTERS WERE TESTED FOR SETTING TIME, STRENGTH, EFFECT OF TEMPERATURES AND ALTITUDE ON SETTING TIME, AND RESISTANCE TO ABRASION. SUCH TESTS UNDER VARIED CONDITIONS WERE NECESSARY BECAUSE OF THE VAGUENESS OF POLICE LITERATURE ABOUT CASTING PLASTER AND ITS APPLICATIONS TO RECORDING CRIME SCENE FOOTWEAR AND TIRE IMPRESSIONS. A DETAILED REPORT OF THE FINDINGS IS GIVEN INCLUDING GENERAL BACKGROUND ON THE KINDS AND QUALITIES OF PLASTER NEEDED IN POLICE WORK, USE OF SALT AND OTHER CHEMICAL ADDITIVES TO ALTER SETTING TIME, METHODS OF TESTING, MANUFACTURER, PHYSICAL DESCRIPTION, AND COST OF EACH PLASTER. TABLES SHOW METHODS OF PREPARATION. (RFC)