In order to produce and preserve the amount of heat necessary for smelting (more than 1000°C), the furnaces that glassblowers used in the I century A.D. were of small dimensions and not unlike those used by blacksmiths. Glass furnaces consisted of a smelting chamber where crucibles were introduced, made of clay or some other refractory material, and containing different vitreous pastes. Glassblowers used the protruding shelf at the mouth of the smelting chamber to rest the blowpipe on and work the molten glass. Next to the smelting chamber, there was probably a low-temperature furnace where craftsmen would rekiln glass to give it its final temper. The first blowpipes used by the glassblowers of antiquity were short and perhaps made of ceramic. At the beginning of the Christian era, blowpipes were made of iron and surpassed one metre in length.