Method of applying light diffusing coating to interior of incandescent lamp envelope

Claim 1

A PROCESS FOR PROVIDING SELECTED PORTIONS ONLY OF THE INTERIOR SURFACE OF A GLASS LAMP ENVELOPE WITH A LIGHT-DIFFUSING COATING COMPRISING THE STEPS OF: A. APPLYING AN AQUEOUS SLURRY COATING CONSISTING ESSENTIALLY OF CLAY AND A HIGH MAJORITY BY WEIGHT OF WATER, TO THE ENTIRE INTERIOR SURFACE OF A GLASS INCANDESCENT ENVELOPE HAVING AN UPPER, CLOSED BULBOUS PORTION AND A LOWER OPEN END NECK PORTION ADJACENT SAID CLOSED BULBOUS PORTION; MAINTAINING SAID ENVELOPE IN AN UPRIGHT, VERTICAL OPENEND-DOWN POSITION; C. PLACING CONDENSING MEANS BELOW SAID BULBOUS PORTION AND IN CLOSE PROXIMITY TO AN AREA CORRESPONDING TO AN ANNULAR SURFACE BAND ON THE INNER SURFACE OF THE UPPER END OF SAID NECK PORTION; D. APPLYING HEAT SOLELY TO SAID CLOSED BULBOUS PORTION TO VAPORIZE WATER FROM SAID SLURRY COATING ON THE INTERIOR SURFACE OF SAID CLOSED BULBOUS PORTION TO DRY SAID SLURRY COATING ON SAID CLOSED PORTION; AND CONDENSING ON SAID ANNULAR SURFACE BAND OF SAID NECK PORTION THE WATER VAPORIZED FROM SAID SLURRY COATING ON SAID CLOSED BULBOUS PORTION AT A RATE SUFFICIENT TO CAUSE THE VAPORIZED WATER TO RUN DOWN SAID OPEN END NECK PORTION AND SUBSTANTIALLY REMOVE THE SLURRY COATING FROM SAID OPEN END NECK PORTION INNER SURFACE BLOW SAID CONDENSING MEANS.