The Gate is is the same color as an old bronze cannon that has been out side for hundreds of years but it is braced with blackened iron bands.Plaid makes a Faux Finish Patina Kit base coat color Patina green.The iron bands are dark gray with a iron oxide patina. Plaid make an iron oxide patina kit as well. This works a little differently than the Faux Finish.The Iron oxide kit contains a paint base that has iron filings in it .You paint it on and then when it is dry you use a oxidizer agent and the iron rust.It can not look more real than real rust. The iron filings in the paint make it course. However, for your application a dry brush over dark gray would produce the effect you want. The copper and bronze patina oxide kits are cool as well but it would be difficult to get the effect in the movie. That is why Plaid makes the Faux Finish Kits. It is much easier to control the effect.
Use the Faux Finish patina green as the base coat. Add a little white to the green for a dry brush. Then use a very light dry brush of pure white. Salts leach to the surface of the metal. GW paints don't have a color that you won't have to blend.That won't help if you can not tell green from red.
You can make this thumb nail much larger.
The chest peace was dry brushed over black. The griffins were dry brushed with Bronze after they were painted with the patina green.The left door was dry brushed with patina green. The Mega Miniatures crypt and right hand Old Glory door were finished with the oxidizer.The Griffins are Mage Knight.
I hope this helps.