Bog Oak (Quercus robur), also called black oak, is the subfossile wood of oaktrees that were felled by natural events and came under water (often in peat bogs or aside rivers) and were conserved there under anaerobic conditions for hundreds or thousands of years. Depending on the time buried, the colour varies from light grey-brown over dark brown to real bluish black. The change of colour is caused by tannin reactions with water containing iron ions, taking thousands of years to reach real black colour. Bog or moor oaks are found when excavating lakes or digging gravel pits in the plains of large rivers. Bog oak is a very rare, expensive wood due to a extremely slow and difficult drying process, which almost always leads to internal cracking.
