If you look at enough heat treated parts, youll see that bronzing on occasion.

In production, it turns out that the wrong alloy was used when the parts were made.

Every so often, somebody that is coloring parts runs into a problem like this, usually a quality control matter in their preparation of their pack, I dont recall ever seeing any evidence that said it was from the impurities in the rain barrel. Bubble size yes, but not impurities in the water.

Out there doing it best I can.