Crystalline additive for magnesium alumina silicate

A process for forming an anistropic polycrystalline part of very fine grain size, low thermal expansion and very low firing shrinkage comprising grinding a magnesium aluminum silicate glass material with 0.2 to 0.5% of ferrous titanate into a fine powder, mixing with the said fine powder a quantity of crystalline powder of the same chemical composition as the glass material the quantity of which is less than approximately 60% and more than approximately 2% by weight, ball-milling the mixture to very fine particle size in the 1/2 micron to 40 micron range, adding the mixture to an organic polymer binder to facilitate forming of the finished part, said binder being capable of being burned off at a relatively low temperature, sintering the fabricated glass particles in a reducing or neutral atmosphere at temperatures of approximately 2,000.degree. F. to effect bonding of the particles together and to trigger crystallization of the particles, the crystallization occurring initially at the surface of the particles thereby increasing the bond strength of the particles and increasing the strength of the material and reducing the thermal expansion.