I stand corrected , its chrome plated
"the Commander 4 Australian Armoured Brigade, BRIG D. Macarthur Onslow recommended that a chrome plated Commonwealth (Rising Sun) hat badge be worn by Armoured Corps personnel on the Black Beret instead of the ordinary copper oxidised badge.
This, he said, would give the Corps a distinctive badge which would also serve as a link with the other Armoured Corps in British Commonwealth Forces which all wore a silver badge. The proposal was approved in 1945.
The Black Beret has been worn by Royal Australian Armoured Corps troops since 1948 on parade and ceremonial duties, in barracks and also out bush on operations. It continues to be worn to this day, however during during the 1990s (circa 1992) the slouch hat with emu plumes was adopted for parades and ceremonial occasions due to the greater protection offered against the sun."
taken from website
http://archive.aweber.com/regimental...er_s_Call_.htm