Yellow ochre is very useful as a “resist”, i.e. a coating that
prevents solder from flowing where is not wanted. I use it on hinges
to prevent the rivet from “freezing”.
Keep a few grams in an open small container ( water proof) such as
the plastic top from a medicine bottle .When needed, mix with a
little water into a medium paste. Cover the area to be protected with
a thin coating, I use the paper end of a match, for instance. After
coating lightly, heat gently, no oxygen, just a little flame. It will
get darker and, voila, solder won’t flow on the treated area. Pickle
after use, it should come off easily.