This is a reverse glass painted (verre églomisé) miniature engraving in original gold-toned (brass I believe) frame, c. 1830s and French. One sees the lids of French patch boxes and bon bon containers executed in this manner, but this appears only to have ever been a portrait, with original papered reverse enclosed by the teeth of the frame. And with the golden butterfly at her shoulder the hinge of the painting, rationalizing the revealing/concealing, innocent/seductive pose that showcases blushing, youthful beauty on the cusp of womanhood! 

2 1/2" x 1 3/4", very good condition. I've shot this with several times magnification which reveals a few dark spots on the frame and a bit of dust/grime caught around the perimeter (which I have not touched), but to the naked eye she appears crisp and bright and all the more lovely.