From the superb Réunion des Musées Nationaux (RMN) site. To find images, go here. When searching for artists - use last names first and do all searching en français si'il vous plait.
RMN has 38 pages of listings related to Catherine de Medici here.
This portrait, after a Clouet original, shows Catherine de Medici wearing a dress with an upswept, crescent, neckline and a partlet covering the space between the neckline of her dress and the neck opening.
Keywords: Clouet - Francois, Blot, Catherine de Medici, Medici family, Valois family, Queen, French, curly coiffure, crescent neckline, French hood, jeweled headdress, jeweled partlet, jeweled neckline, jeweled bodice, jeweled bodice ornament, jeweled sleeves, necklace, earrings, draped necklace, French sleeves