For centuries, gold has been used to make stained glass -- and not just golden-hued glass, either. When it's broken down into  nano-sized particles -- we're talking billionths of a meter -- the precious metal stops being gold colored and reflects a deep crimson red or a light blue. Nanoparticle gold also has a wide variety of other uses --  especially as a chemical catalyst. Using gold as a catalyst in making paints and adhesives could lead to the elimination of toxic mercury from the process. In chemical processes, a gold catalyst can lower both the temperature and pressure needed to start a reaction, thereby reducing the amount of fuel needed -- and thus the cost of production.