-DEVELOPMENT OF RESIDUAL COMPRESSIVE STRESSES The fabrication of metal-ceramic and all-ceramic prostheses usually involves sintering the ceramic at high temperature or hot-pressing a veneering ceramic onto the metal or core ceramic. The process of cooling to room temperature offers the opportunity to take advantage of mismatches in coefficients of thermal contraction of adjacent materials in the ceramic structure.  -MINIMIZING THE NUMBER OF FIRING CYCLES The purpose of porcelain firing procedures is to densely sinter the particles of powder together and produce a relatively smooth, glassy layer (glaze) on the surface. In some cases a stain layer is applied for shade adjustment or for characterization, such as stain lines or fine cracks.  -ION EXCHANGE The technique of ion exchange is an effective method of introducing residual compressive stresses into the surface of a ceramic.  -THERMAL TEMPERING Perhaps the most common method for strengthening glasses is by thermal tempering, which creates residual surface compressive stresses by rapidly cooling the surface of the object while it is hot and in the softened (molten) state. This rapid cooling produces a skin of rigid glass surrounding a soft (molten) core. As the molten core solidifies, it tends to shrink, but the outer skin remains rigid. The pull of the solidifying molten core, as it shrinks, creates residual tensile stresses in the core and residual compressive stresses within the outer surface. Philips’ Dental Material, pg- 440, 441