We have almost completed some timberframe highlights on a house we are building. 

There are some 4″ steel pipe posts amongst the timbers.  Yesterday I ground the posts to height. 

Today I showed up and all the timbers in the area had black dots and streaks all over. 

The stock is reclaimed fir that we have resawn.  I hit the fir with a wire wheel on a grinder, and it helped a bit, but it is still ugly.  Short of resawing does anyone have any suggestions on how to get rid of this staining?