Fantastic Portrait Miniature on Bronze with Enamel

I know I have seen this before - reminded me of some Vienna /KPM style miniatures only this is on bronze with impressed initials under the foot. Really fantastic portraits in beautiful enamel which reminds me a bit of plique-à-jour. I thought the works were on ivory but I am not seeing any cross hatching or schreger lines (possibly where there is fine painting of the face). There are two marks impressed into the foot. Very hard to photograph but one is LP and the other looks like an A. Could this be Louis XV and Madame Pompadour? Any help would be greatly appreciated. Approx. height 4.12".