Silica sol is a kind of milky colloid. Since the colloid grains are minute (10-20micrometer) and have relatively large surface area, so they do not affect the natural color of materials to be covered. Silica sol is mutually soluble with water , but not with organic solvent. It can dissolve in a solution of alcohol or water mixed in any ratio. The distinguished feature is that with low viscosity, it can soak the places where water soaks, therefore, silica sol presents excellent dispersion and permeability when being mixed with other substances. When the moisture contained in silica sol is evaporated, the colloid grains firmly adhere to the material surface and the combination of silicon and oxygen is then formed between grains. It is a good adhesive. That is the main function of silica sol as an molding adhesive for stainless steel investment casting.