The colors of the oxide layer vary depending on the thickness of the layer and the angle of light that is reflected off of it. The patterns of Attractive bismuth jewelry are also created by the way that the metal is cooled. When bismuth is cooled slowly, it forms large, hopper crystals. These crystals have a distinctive shape that is reminiscent of a mushroom or a funnel. When bismuth is cooled more quickly, it forms smaller, more intricate crystals.