strange Alclad reaction

The thing that tickles me is that the rest of the airrame allu went over the enamel beautifully.

The affected area lookd exactly like the rest of the airplane BEFORE I shot the pollished allu over the airframe allu.

SOmehow the pollished allu ate through the other alclads and enamel to foil the plastic.

I have in the meantime masked and sanded back the area, will re-black it and then try again.

Theuns