Hi Dan,
The process is pretty much the same, only difference is you are adding Bronze powder to the mix, there are two ways to do this, one is you add heaps of the powder to the actual resin which will will give the finished cast a bronze effect and a hefty weight to it. The other way is that you brush the inside of the mold with bronze powder before pouring the resin, the end casting will be bronze but only on the outer surface, this is a far cheaper option as bronze powder is not cheap.
I have tried both options and I liked the first one due to the piece felt heavy and more like a real bronze casting. One thing I did do was colour my resin deep brown which gives a better result with the bronze powder.
If you look on youtube there are plenty of videos showing what to do.
All the best
Steve