blotchy shellac on pine slab

[William Hamilton]

Man, this "simple" refinishing project for a friend is becoming frustrating. Aside from "discovering" metal in the slab while flattening(and killing two bits), I did one coat of thinned dewaxed shellac and it resulted in this appearance. I was careful in my application so now I am wondering if the wood is contaminated with something from days gone by. The darkened areas seem to be around where the checks are. I don't think its a natural occurrence. That leads me to wonder about contamination. Now I'm a bit stuck because I do not like how this looks or how to remedy it. I know pine can be blotchy but I did not think the shellac seal coat would be an issue. Any thoughts?
Thanks,
Williamshellac.jpg

[Tom McMahon]

Pine naturally ages to a pumpkin color, It appears to me that you have sanded through the aged surface in some areas and not in others. I don't think the shellac is the problem.

[Wayne Lomman]

It looks to me that it is either what Tom says, or it could be contamination or the presence of moisture all of which relate to it being a problem with the slab itself. Check with your friend and make sure it hasn't been wet in the recent past - assuming it is old enough to be properly seasoned. If this is the problem, dry it for a time and try again. If it is sanded unevenly, sand it again. This may also solve the problem if it is contamination.

If this doesn't work, how good are you at colour matching? Careful choice of almost colourless stains to blend the finish into a unified appearance is possible but you will need a good eye for colour and the skill to apply colour with whatever technique make the colouring undetectable. I would probably sand the daylights out of it and polish again though.