Abstract: A method of making a fritless seal in a ceramic arc tube body comprises the steps of: (a) inserting a feedthrough into an opening in a ceramic arc tube body, the feedthrough being comprised of niobium or a niobium alloy; (b) heating the arc tube body to a first temperature in an inert gas to at least partially sinter the arc tube body, the inert gas being selected from the group of argon, neon, krypton, xenon and mixtures thereof; and (c) further sintering the arc tube body by heating to a second temperature in a hydrogen atmosphere to form a hermetic seal between the feedthrough and the ceramic arc tube body, wherein the second temperature is higher than the first temperature.