to 1 8oral oh sub 3 12 to 2 5 0 61 to 1 9mantle proportionsafter firingy sub 2 o sub 3 100 100ceo sub 2 1 8 to 3 8 2 9 to 3 5mgo 0 1 to 2 0 0 5 to 1 5oral sub 2 o sub 3 0 1 to 2 0 0 5 to 1 5______________________________________ in the foregoing tabulations of relative proportions the amounts of the other metal compounds are on the weight basis of 100 parts of the yttrium compounds for example the mantles after firing should contain from 1 8 to 3 8 parts by weight of cerium oxide per each 100 parts of yttrium oxide it is also desirable to include from 0 1 to 2 0 parts of the crystal grain growth inhibiting metal oxide such as magnesium oxide or aluminum oxide berylium oxide will also serve this purpose but is less desirable for commercial use in the preferred formulation from 2 9 to 3 5 parts by weight of cerium oxide will be employed per 100 parts of yttrium oxide together with from 0 5 to 1 5 parts of magnesium oxide or aluminum oxide per 100 parts of yttrium oxide the corresponding proportions of the hydroxides and nitrate of the metals are set out in the tabulation other corresponding values can easily be calculated for rapid impregnation of the mantle cloth in a single soaking and drying sequence it has been found desirable to employ a warm relatively concentrated aqueous solution after soaking in.