Permeability of Investment at the Casting Temperature

¹ Ransom & Randolph Co., Toledo, Ohio

Equipment and technique are described for measuring the gas permeability of investment at burn-out temperatures and at pressures corresponding to those employed in dental practices.

It is difficult to obtain reproducible readings on different specimens. This may be due to the large variations in the amount of voids present in poured investments. Vacuum investing increased permeability. Burnt-out wax increased permeability. Longer burn-out time and higher temperatures were found to decrease the permeability of some investments. Using a water-added investment, the permeability through inch of investment should allow cc. of gas to escape in less than 1 second.