I know this is a late post, but I thought it might help others.
I make "Shabby Chic" style furniture and often need to make stuff look old when it's not. Take 1 piece of 0000 steel wool and tear it into small pieces. Put it into a quart glass jar and fill with distilled white vinegar. Let it sit for a day or two, shaking ever so often. The steel wool will dissolve in the vinegar and then you can just paint it on to your new board. When the vinegar evaporates the dissolved metal will have been soaked into your board and will look just like it came off the side of an old barn! Good Luck.