Wood that has fallen will sometimes have interesting colouration caused by fungii known as spalting. This can be simple colours such as yellows, pinks and purples, or in the case of this bowl the more classic black lines which is a mineral deposit. The dried wood is quite harmless to humans. The spalting adds a level of interest to the visual bowl, and each piece will be as unique as a fingerprint! This is a bowl from a set of three blanks which I bought, but each one is slightly different, and I have also given them a different shape.