"Portrait of a beautiful lady holding a mask", Jean-Marc Nattier
Portrait of a lady, presumably marie louise élisabeth d'orléans (1695-1719)
identification proposed by user ecummenic (talk) based on the comparison with some portraits of that princess painted by pierre gobert (see images below). Date: between 1700 and 1725 (the approach is based on the sitter's clothing and hairstyle). Dimensions: height: 24 cm (9.4 in); width: 20 cm (7.8 in). Medium: oil on canvas. Collection: Unidentified location. Studio of Jean Marc Nattier - Portrait of a beautiful lady holding a mask