Abstract: A sealing composition is provided for joining crystalline ceramic or cermet parts, e.g. in an arc tube for a discharge lamp. The sealing composition comprises, as starting materials, a mixture of alumina (Al.sub.2,O.sub.3), silica (SiO.sub.2) and magnesia (MgO), the mixture comprising in the ranges of from 22% to 24.5% by weight of Al.sub.2 O.sub.3, from 45.5% to 49.5% by weight of SiO.sub.2, and from 26.0% to 32.5% by weight of MgO. The sealing composition contains less than 40% by weight, of the mixture, of the crystalline phase .alpha.-Cordierite when subjected to the following test procedure.(i) sintering the mixture at 1200.degree. C. for 10 hours to produce a friable lump which is crunched and heated at 1550.degree. C. for 2 hours while the glass is in a molten condition;(ii) pouring the resulting material into water to form a brittle frit and, after drying at 160.degree. C., grinding the glass to a powder particle less than 180 .mu.

Abstract: A lamp capping cement for electric lamps comprises a resin component consisting essentially of a condensation product of an aralkyl ether and a phenol mixed with a cross-linkable polymer or resin, a heat-resistant filler component, and a liquid diluent. The preferred cross-linkable polymer is a carboxylated acrylic polymer which may constitute 1 to 15% of the cement. This cement is capable of withstanding higher operating temperatures in incandescent filament lamps without breakdown.