Some copper water pipe solder fittings have a residue of green gunge
around them, due to the finished solder joints not being effectively
cleaned after soldering.after new CH installation around 5 years ago.

First Q: What is the green gunge (chemically)? Does the deposit have
common or garden name? It must be a Cu compound, but how is it formed
from solder flux, copper, solder & propane gas used in the torch?

Second Q: What is the most effective method of cleaning it off,
especialy when it has been on the Cu pipes several years? I'd like to
get the area around the fittings reasonably chemically clean. I fancy
just cleaning with wire wool might leave a residue for the green to
re-crystallize on.

Third Q: I thought I had cleaned the joints at the time, so how should
soldered work be cleaned to avoid green film formation?

TIA