Built up applied copper finish from 1920-30s, Brisbane City Hall

I am an architect researching the decorative finishes in a room in the City Hall (completed 1930) in Brisbane, Australia. I have found a copper finish on both pressed metal (original finish) and plaster (this has been overpainted). The finish appears to be built up - the first coat is dark-brown black, the second coat has copper particles in it. I believe there is probably a lacquer over this as the finish has not aged very much although I can't be certain with my 20-power lens. I am waiting to have the paint analysed by an art conservator but I am wondering if anyone else is familiar with this type of finish? whether it was in widespread use for finishing decorative pressed metal during that period. I know I have more research to do but I was curious if anyone else knows about this.

Try to find professional metalwork conservator-there are many of them "down under". Conservation OnLine website is good starting point. Good luck!