that's a great picture to show all the guys who rave about white or red oak beds. Oal is extremely pourus and will turn black inside the pours when exposed to any moisture.

SCD hit the nail right on the head. You will have to remove any remaining finish, then bleach the oak to remove the black - sanding will not do it as it is INSIDE the pours.

In addition to the woodworking stores, boat shops and decking shops carry the acid. The one I use on my boat is actually a combination of bleach and acid, and rubbed in with a pumice stone (very similar to the Holystonning they used to do on the teak wood decks of Battleships)

The Mar-K site is a great reference. They have a section with finishing methods and test data from various finishes.

Just be certain that you "Fill" those pours with a good oak wood filler (not wood dough type filler but the cream type used on oak flooring) and all your finishes are rated for exterior use - such as a WATCO type teak oil and Spar varnish, etc.

http://www.mar-k.com/