Copper Tube

Why do we here in Italy use copper tube for drain pipes and chimney flues?

A new length of copper double insulated tube arrived today at Bellaugello gay guest house for the external section of the flue for the Mirror Suite stove that is being installed into the old fireplace.  It is shiny and gleaming, but soon will become dull and tarnished as is the piece that currently goes through the roof on the upper part of the house to which it will connect.  Almost at the same time I was at the builders’ merchants buying drainpipe and guttering for the new entrance to the Diva Suite.  In the store were metres and metres of gleaming copper pipes and connections, I chose from them.

How do they keep it clean?  Do they use brasso?  All I know is that the copper pipes we mounted on the house last year are now dull, maybe I should have lacquered them or bought ordinary tube and maroon matt paint…..