Well thank you very much although it was not down to my skill.
Skullyboy, your criticism only shows one thing: I am really, really bad at taking pictures. Yes, I need to improve it, it is becoming annoying...
Here is a picture in front of an off-white background.

It is quite realistic, because, well it is real.
There is an manufacturer in the US (with subcompanies in Europe) which sells a range of paints called Metal Masters. These are not intended for painting miniatures, but for furniture and room decorations. But that doesn't mean we can't use it. There are three sets for rusting and patina. Dark iron with rost effect and copper with green patina and bronze with turquoise (although they call it blue) patina.
I am not in any way related to this company and have to say the prices are a bit off-turning, but it is still very cool for statues and things like that. And easy.
Here is some advertising video showing how to gain the effect with the copper paint.
The starter set I bought consists of a primer, the metal paint, the aging spray and the sealer.
PS: The metal base actually consists of iron, copper or bronze, so you have the real oxidation effect.