The process of electroforming is becoming more and more popular in the glass industry. This process is often confused with electroplating, and there is one main difference. usually electroplating is coating a metallic item in thin layers of copper, where electroforming usually involves coating a nonmetallic item in copper. In the case of glass pipes, bubbler, and bongs it is considered electroforming.
Electroforming is actually a fairly simple process. It uses electricity and current to take copper from a solution and deposit it on to the surface of whatever you want to coat. Since glass is not electrically conductive on its own, anywhere you want copper, you need to spray it with a conductive solution. Then the piece needs to have wires attached to the piece so an electrical current can be passed through the glass.
It is then submerged in a bath of copper solution. The bath must have another electrode placed in it. When an electrical current is run from the electrode to the wires, it causes the copper to be attracted to the conductive material that was sprayed on the glass. Over the course of a few hours layers of copper will build up anywhere the conductive spray is. Generally it takes anywhere from 2-8 hours to cover something, depending on how thick you want the copper to be.
This is how they make the awesome copper plated bongs, bubblers, and pipes we have come to love!