Good slurry adhesion during application of primary coats is critical to achieving excellent surface finish of precision investment castings. Non adherence of the primary slurry onto the wax surface due to presence of residual mold release leads to lifting or buckling of the prime coat and subsequent bulging on the surface of castings. The consistency and cleanliness of wax pattern surface requires good pattern wash practices and maintenance of the solvent. Repeated dipping of patterns in pattern wash tanks invariably leads to a drop in the solvency power over time thereby reducing their effectiveness for cleaning and etching. Determing the end life of a pattern wash has not been well established. The purpose of this study is to develop a simple quantitative 'cloud-point test' for ranking solvent power of pattern wash that can be used within the PIC foundry. A series of trials for varius pattern wash products were conducted to establish limits for solvency power. The solvents were subjected to repeated application of mold release and wash cycles with Remet 288B and HF 1417 wax patterns and then evaluated for effectiveness. Benefits include improved process control and cost avoidance by preventing contaminated patterns from entering shell mold production downstream.