Here is what goes on.... I bend a thin wall brass tube to shape then I have
to melt the bending medium out of the pipe with a torch. This causes a
black scaling to show up on the outside of the pipe. To remove this I dip
the pipe in a 50/50 mix of muratic acid and water. This in turn plates the
pipe with very thin copper that I have to buff off.

I know the acid is leaching copper and plating later pipes but what is the
science behind this? Why does it plate?

LLB in Laredo