About phenol formaldehyd plastic oxidation

Hi everybody,

I am kind of in a weird situation....

I have a phenol formaldehyd plastic. This plastic is oxidized (it takes months to fully oxidize. When it oxidizes, its outer colour turns a bit darker than the original one. As you can see on the picture below, original colour is a cloudy white but when it oxidizes, its colur turns to dark red. I have several different colours of materials, all of them turn to a dark colour, some of them dark red and some of them to dark brown, or black. It depends on the original colour.

What i want to do is to make this oxidation faster. Anyone can tell me the main principle of this oxidation (what would be conditions, what makes the material oxidize, what conditions trigger it to oxidize etc). Any response will be appreciated.

Please see the oxidized material below. I grind a little part so you can see the original colour.

Regards.