From Wikimedia.
The skirt appears to be made of large-pattern lace on a sheer background beneath or between bands of fur. Here is the drapery that would become codified in mantuas in the years after 1684.
Keywords: Curlando, Marie Jeanne de Savoie, Marie-Jeanne-Baptiste de Savoie, Maria Giovanna Battista di Savoia-Nemours, Mademoiselle de Nemours, duchesse d’Aumale, Duchessa di Savoia, Princess, Duchess, Countess, Savoia family, curly coiffure, earrings, lace-edged chemise, off shoulder scoop neckline, elbow length full under-sleeves, lace flared cuffs, fur-trimmed over-dress, quarter length full flared over-sleeves, bracelets, fur girdle, vee waistline, lace close under-skirt, fur, regalia