Abstract: A diamond sintered product having diamond particles sintered with a suitable sintering aid is the most suitable as the material for the mold for optical element molding, because it has in combination the advantage of diamond that no fusion with glass at high temperature occurs and oxidation occurs with difficulty to give rise to no precipitation of lead, an appropriate hardness and also the advantage that mirror polishing is possible. "There is also disclosed a mold which has a diamond layer having a (100) face, made by the CVD method utilizing gas having 1-3% methane in hydrogen.

Abstract: The present invention relates to a method for making a glass article having at least one surface which is essentially defect-free and is at least equivalent in smoothness to a polished surface. The method includes the steps of:(a) bringing into contact with each other a body of a glass which is relatively insoluble in an acid solution and a body of a glass consisting essentially, expressed in terms of cation percent on the oxide basis, of 70-85% B.sub.2 O.sub.3, 7-20% BaO, 0-10%, PbO, 0-12% R.sub.2 O, wherein R.sub.2 O consists of Li.sub.2 O+Na.sub.2 O+K.sub.2 O, 3-15% PbO+R.sub.2 O, the glass from its setting point to room temperature having a linear coefficient of thermal expansion within about 5.times.10.sup.-7 /.degree.C. of that of the relatively insoluble glass, a strain point within 10.degree. C.