Some Factors Influencing Specific Gravity Determinations on Gold Cast Alloys

¹ The George M. Hollenback Research Associates, Encino, California

The specific gravity of an M.O.D. type casting of approximately 1 dental dimensions increased with the sprue diameter for 16-, 14-, and 12-gauge sprues.

There may be a slightly higher specific gravity in castings made by a temperature-controlled casting machine over those made in a pressure or vacuum machine.

The use of a reservoir had no effect on the specfic gravity when using 12-gauge sprue. Changes in specific gravity may not be interpreted as changes in porosity unless chemical analysis made is made.

There may be a slight increase in specific gravity on repeated castings resulting from changes in formula of the metal.

Casting at 2,200° F., as opposed to the usual casting temperature of 1,925° F., produced an insignificant increase in specific gravity that probably resulted from increases in the gold content of the metal overbalancing increased porosity.

The presence of "back pressure porosity," caused by a long distance from the wax to the end of the investment, no asbestos liner, and an exceptionally thick mix, could not be demonstrated.