We have these skylights in our house with wooden frames, and every spring for years I have been fighting the battle against fuzzy grey and black molds that spring up on the wood over the cool, damp winters. But now, I believe I have won the battle, because this is the first year the mold did not come back in full force.
Here is my technique for mold eradication:
1. If the mold is obviously occupying a third dimension in space (i.e. sticking up from the surface), vacuum or wipe up the mold with a cloth.
2. Mix Borax/water in a 1:10 ratio and scrub the mold with this solution using a scrubby sponge or wash rag. Let it dry.
3. Put a 3% Hydrogen Peroxide solution into a spray bottle and spray on the mold-plagued surface. Let it sit 10 minutes, then scrub.
4. Put straight white distilled vinegar in spray bottle with a few drops of tea tree oil. Spray this on and leave it on.
Spray the solution described in step 4 periodically to prevent mold.
Why use so many different substances? Because different molds get killed by different substances. So this technique is like a multi-pronged attack.
I believe the secret ingredient for my particular mold is tea tree oil, because in years past I did this procedure without it and the mold always returned.