Door Knocker Metal I.D Request

Started cleaning this door knocker, that was found whilst removing the remains of a tree. Did not get very far into the cleaning when I noticed that there appears to be two different types of metal. I don't know if it's me going mad. I have placed it under different artificial lighting and the colours are very different. The front of the knocker is more of a reddish(rose gold) colour and the back is yellow, which would suggest, copper and brass. If so, what would of been the reason for making it this way I wonder.

I have looked at different sites and images from google, but unable to find one matching. Any help is appreciated.

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