We purchased a lake cabin and are starting to renovate the bedrooms. I pulled away a plywood panel to expose black sheets of insulation. After doing some digging - I have settled on the fact that the insulation is rockwool from the 60s (premium brand with the Indian head logo) Each panel of insulation is wrapped in kraft paper but the paper is almost totally black where the insulation meets the interior wall. The other side of the insulation that faces the exterior of the house looks like almost-new, brown, Kraft paper. Is there anyone who can explain why it looks this way? I originally had mold on the brain to explain this - but everything I read says rockwool is resistant to mold.