A dentist can best control the setting time of alginate impression material without altering its properties by:

A slight modification in the W/P ratio or the mixing time can have marked effects on two important properties of the gel, tear strength, and elasticity; thus, the setting time is best regulated by the amount of retarder added during the manufacturing process. Usually, the manufacturers make both fast-setting alginate (1.5 to 3 min) and normal-setting alginate (3 to 4.5 min) to give clinicians a choice of the materials that best suit their working style. Clinicians, however, can safely influence the setting time by altering the temperature of the water. The higher the temperature, the shorter is the setting time. The temperature of the mixing water should be controlled carefully within a degree or two of a standard temperature, usually 20°C, so that a constant and reliable setting time can be obtained. In hot weather, special precautions should be taken to provide cool water for mixing so that premature gelation does not occur. It may even be necessary to precool the mixing bowl and spatula, especially when small amounts of impression material are to be mixed.