We're sanding and refinishing our new 1900 American Foursquare in Portland, OR. Now that we've gotten the first layer of finish off with 36 grit, we can see there are some fairly large areas of discoloration. I'm not sure what caused it, though.
I've looked up ways to lighten the wood, but they're generally based around removing pet urine stains. I don't think that's what is happening here.
Looking for help on 1) how to lighten/remove those stains and 2) if we should do that now in the rough stage of sanding or if we can keep going through the grits and deal with it at the end.