My Oak has gone black! How do I remove the staining?

Ever since I wrote the guide to painting or staining gates and doors, I’ve been emailed or phoned hundreds of times about a problem a lot of people (not our customers, I must add) are having with their products, be it garage doors, front doors, gates and even garden furniture usually in Oak.

It usually something like: my Oak gates or garage doors have gone black and is this normal? Why have they gone black and is there anything I can do about it?

Black stained Oak

For example (the picture above accompanied this email):

Good evening,
I wonder if you wouldn’t mind giving me some advice.
I purchased some Oak gates in 2013 and since then, I have been treating them with Cuprinol Teak Oil every year. Over time, they have lost their colour (see photographs attached).
Does this look like natural weathering or is the wood infected with a fungus and in need of washing with a fungicide or mild detergent?
To restore them, would I need to sand down or just apply a good quality stain?
I would be grateful for any help you can give.

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