caffeineme wrote:What are those barnacle looking things stuck on the mushroom then?

The greenish blob deposits on the mushroom would contain some form of copper salt - copper chloride, sulfate, carbonate and acetate all have blue or green colors. These tend to build on areas where the plating has flaked off of the brass mushroom (brass is a copper alloy) and the copper is reacting with salts in the water. I've often wondered why they appear so readily on the mushroom but not on other brass parts. Perhaps it's somehow related to galvanic corrosion of the nickel plating and the brass body?

caffeineme wrote:Are the deposits on the "piston" limescale?

Hard to tell. Limescale is calcium carbonate, and you can check -- scrape some off into a cup and pour some vinegar on it. It will fizz if it's a carbonate.

Taken 4/16/2020. Not much changed from last look.