This is a really neat phenomenon in the glass world. To help answer this we must take a step back into history. Some of the first glass pipes to come to the scene that are color changing pipes were from a guy named Bob Snodgrass. This guy stumbled on to the fact that if you get the precocious metal hot enough they will turn to a gas or vapor and then fume onto the piece of glass you want it on. Before this revolution there we no colors in the borosilicate world, so the only way to get color was to make your own. The use of cobalt was coming into play and some renegaded artists were mixing cobalt and anything else they could get their hands to change the clear borosilcate glass.
Knowing that pink and red glass was made by using gold, Mr. Snodgrass decided to try this fuming technique. Making pink and red glass using gold is actually the first nano technology known to man. Gold is actually red at a microscopic level, so this is why gold fumed glass has a pink look to it.
HOW THE COLOR CHANGING PIPE WORKS
Basically the color changing pipe does not really change color. What happens is that when the glass is clean and clear the gold and silver a see through. This allowing much of the light to pass through the glass. As you smoke your pipe and it gets dirty from the resin, the black resin does not allow the light to pass through the glass. This allows the light to almost reflect back through the gold and silver fuming. As this happens over time from smoking, the pipe will appear to change color. The light colors you could not see will begin to really pop!
WHAT MAKES THE COLOR IN A COLOR CHANGING PIPE
Some people call this a chemeleon pipe as like the lizard the pipe changes colors as it is used. One of the first companies to ever sell a fumed pipe was Chemeleon Glass.
Silver- When someone fumes with silver properly you get blues and purples. This is an art form to get the perfect amount of silver fuming. If one goes too light you will get some purples later on as you use the pipe. If the artist goes too heavy on the silver fuming the pipe will not change color and you will see this milky white on the glass. Stay away from this as the artist just was not up to par to produce a color changing pipe.
Gold- When the artist fumes with gold you get pinks and oranges. The lighter the fume the more pink you will get, while when fumed heavy the color changing pipe will get more oranges. If the artist fumes extra heavy the glass will turn to gold as the gold is now many atoms thick. Note that to use gold the color changing pipe must be fumed with silver first. For the artist to get pure gold fuming, the piece is fumed with silver and then most of the silver is burned off. The gold will not stick to glass, but it will stick to the silver. Even if the silver is only 1 atom thick, it now has a surface to stick to.
Gold & Silver- When a pipe is fumed with both of the precious metals pure magic happens. With the right combination the artist can get an amazing color green. Its just so amazing how the red and blue make green. We have no idea how this really happens other than maybe it truly is magic. When the artist has this technique mastered he or she will be able to have the pipe go from pink/blue hues to rich blues, oranges purples and that amazing metallic green.