For centuries people have been coloring glass. In fact turning a clear piece of glass into one that has a reddish glow is not that complicated. The procedure is very simple. Natural glass is green or greenish-blue because of the iron oxide that is present in the sand. To get clear glass you add manganese, for red glass you add copper and gold dust. This makes red glass very expensive. In order to achieve a reddish tint, one must heat a normal piece of glass at 550 degrees Celsius. It is unusual that no oxygen can interfere with the processes. This miraculous transformation is believed to come from the change of shape of the gold clusters that were put on to the glass when it was heated. The longer the piece of glass is confronted with heat, the more change in color the glass will experience. The more a piece of glass is heated, the darker it will turn. Red is not the only color glass can change into. If you heat glass with manganese, you will get a purpleish color. Chromium sprinkled onto a piece of glass with the help of heat will make the glass turn green. It is amazing that glass combined with different elements can change glass's orignal color to an amazing number of different colors, just by heating the glass.