Lead glass tubes are made by skilled glass blowers. Typically they range in thickness from 8 to 15 millimeters. While the glass is still hot and partially molten, it is shaped to match the design for the neon sign. One end of each tube is closed off, and the other is attached to an atmospheric vacuum pump. All the air is pumped out of the tube. This continues until the glass tubes have cooled to room temperature, though by then metal electrodes have been inserted into either end of each tube. When the tube is cool, the vacuum is reversed to pump the tube full of noble gas. A dab of molten glass is pasted over the open end. The tubes are then mounted onto a metal framework, and all the electrodes are connected to a single electrical cord with an outlet plug. All a user needs to do is plug it in.