Rare Antique French Portrait Miniature, Artist Signed Kiln-fired Enamel of Marie-Antoinette on Tortoise Shell Snuff Box

Fabulous French kiln-fired enamel portrait on copper plaque, signed by the artist, "M. Louvet", incorporating the pale grisaille in portrait silhouette against a darker but rich background, a little foil worked into her hair ribbon's bow and her gown which reveals the signature at her shoulder. I do believe this is Marie-Antoinette, a likeness in her nose and profile. Perhaps done in early 1800s, though I haven't been successful locating an earlier original profile portrait of her after which this enamelist might have worked. Beautifully crafted, this is truly the most arduous of methods, a skill that takes decades of apprenticeship to achieve this outcome. Porcelain powders are worked on a copper or sometimes silver plaque, then kiln-fired to melt into a glassine finish, but those powders are all shades of mauve to blue to mud, and one works by remembering what each will become once melted. Tremendous skill, most famously by artisans of Limoges, but also Sevres and Bresse, France.  Th