Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Looks to me like that boiler was filled with some very bad water and left standing with a slow weep for a very long time.

There are many tap water contaminants that can be pretty corrosive/reactive over time. The question in my mind is how much of what we are seeing is just evaporite deposits, and how much is actual corrosion. It is not uncommon for evaporites to take on the colors of the host containers metals, but often in fact very few molecules are involved, so that the actual amount of corrosion is minimal in spite of the colorful appearance. No way of knowing what the story is in this case without taking the plunge and seeing what is what in person I'm thinking!