Bed Wood Problem

[Shaun1162]

So, I have a problem with the bed wood I just finished for my flatbed. I used red oak, and used a 50/50 mix of linseed oil and turpentine, after several recommended it. I coated all 4 sides, as well as the ends, plus coated the holes that we drilled for the bolts (all stainless steel).

The wood received three coats of the 50/50 mix before we put it on. It's been indoors drying for about a week now. Today, I backed the truck out to wash it. I got some water on the wood, but didn't think much of it until I was walking by later and saw a bunch of black spots all over the wood. It almost looks like a black mold on it? There's more stains around the bolt heads, but theres still spots throughout now.

Anyone have an idea what the stains are from? The stainless steel bolts? Or how I can maybe get them out, or prevent it from happening again?

Any help is appreciated... Really discouraged from it