DENTAL amalgam is incorporated into about 80% of all dental restorations. It is prepared by grinding or triturating a silver–tin alloy (Ag3Sn, the γ phase) with mercury in the proportions 1 : 1 or 5 : 6 of alloy to mercury. The setting reaction of dental amalgam has been studied by many workers1–4 and is now accepted to be Excess mercury is removed from the amalgam both before and during insertion into the cavity. There is, however, some controversy over whether the γ2 phase is continuous throughout the matrix5 or whether it is present in discrete clumps or clusters (G. Wing, personal communication).