Depends on what you mean by worn bronze. Do you mean oxidized? Do you mean dirty and beaten up?
I usually do bronze the folowing way:
1) Base coat with
GW Dryad Bark
2) Apply the Bronze paint of choice, I prefer
GW Runelord Brass (Ignore the name, it looks like bronze the color matches better)
3) Wash with
GW Agrax Earthshade
4) Go over largest areas with thin layer of Runelord Brass again.
5) If you want it to look oxidized, take a blue/green color, dilute it and wash it in the recesses.
GW makes a paint specifically for this called Nihilakh Oxide. (Under technical paints on the website)
Hope that helps!