Since glass cools quickly when it is out of the furnace, about every 30 seconds it must be reheated in a "glory hole''--a very hot furnace that does not contain a tank of molten glass. Later on when the ball of glass is somewhat larger, it needs to be reheated only about every minute. If he lets it get too cool it will crack. If it is too hot, it will run off the end of the blowpipe.
