Heat mirror for incandescent lamp

An electric incandescent lamp comprising a sealed regularly conformed hollow thin-walled light-transmitting vitreous envelope, a heat mirror carried on the interior surface of said envelope, said heat mirror operative to substantially transmit visible radiations and to substantially reflect infrared radiations, incandescent filament means of coiled configuration operatively positioned within said envelope so that infrared radiations emitted therefrom during lamp operation will be reflected by said heat mirror to impinge upon said filament means thereby to enhance the conversion of electric energy to visible energy, and said heat mirror having been formed on said envelope by the process which comprises:

• a. applying to the interior surface of said envelope, to a substantially uniform predetermined thickness, a clear solution having contained therein partially hydrolyzed metallic alkoxide which in the metallic alkoxide form prior to hydrolyzation is expressed at M(OR).sub.n, wherein M at least substantially comprises titanium, R is alkyl with from 1 to 6 carbon atoms, and n is the valence of M;
• total reacted and unreacted water in said solution being present in amount of from 0.6 mole to 8 moles per mole of said metallic alkoxide;
• the solution solvent being liquid aliphatic alcohol present in amount to provide a solution solids content, expressed as equivalent metallic oxide, of from about 0.1% to about 3% by weight;
• and as an optional constituent, said solution is acidified with at least one of hydrochloric, nitric and perchloric acid in amount of up to about 0.3 mole per mole of said metallic alkoxide;
• b. heating said envelope and first applied solution to a temperature of from about 300.degree. C. to about 600.degree. C. but not exceeding the strain point of said envelope for a sufficient period of time to convert said applied clear solution to an adherent thin continuous metallic oxide layer;
• c. applying over said first applied metallic oxide layer a thin continuous silver layer of predetermined thickness sufficient to be substantially transmissive for visible radiations and substantially reflective for infrared radiations;
• d. applying over the applied silver layer to a thin substantially uniform predetermined thickness a second clear solution as used to apply said first-applied metallic oxide layer;
• and
• e. heating said envelope and applied second clear solution to a temperature of from about 300.degree. C. to about 425.degree. C. under conditions which are non-reactive for silver for a sufficient period of time to convert said second applied clear solution to an adherent clear metallic oxide layer.