OPTION 4

֍ The α-hemihydrate form of gypsum is generally the binder for investments used in casting gold-containing alloys with melting ranges below 1000°C. When this material is heated at temperatures sufficiently high to completely dehydrate the investment and to ensure complete castings, it shrinks considerably and occasionally fractures.
֍ The strength of an investment is usually measured under compressive stress.
֍ The compressive strength is increased according to the amount and the type of the gypsum binder present.
֍ For example, the use of α-hemihydrate instead of plaster definitely increases the compressive strength of the investment. The use of chemical modifiers increases strength because more of the binder can be used without a marked reduction in thermal expansion.
⸙ KEY CONCEPT:     
֍ The strength of an investment is usually measured under compressive stress.
֍ The compressive strength is increased according to the amount and the type of the gypsum binder present.