I have looked at various sites washed bowl in washing up liquid and allowed to dry naturally it is a lot better. Looked at moutain woodworker and a number of other sites. Prob will try oxalic acid (wood bleach) it seams that it may be because the wood got damp and the moisture reacted with tanins in it. If I sand it the stain may be deep into the wood. Also I can't really sand as it has our names and the date of our wedding round the rim of the bowl and intertwined initials in the centre. It was a wedding gift from a friend. Thank you everyone for your suggestions.