The wooden frame carries a board holding wooden sticks of triangular section. If we view the board from the top toward the lower front, the row of visible sides of the painted sticks displays the portrait of Charles III, Duke of Lorraine; if, using the mirror placed in front, we observe the arrangement from the opposite side, we see the portrait of the Grand Duchess Christina of Lorraine, daughter of Charles III and wife of Ferdinand I de' Medici. A very similar apparatus was described by Egnazio Danti in his commentary on Jacopo Barozzi from Vignola's Le due regole della prospettiva [The two rules of perspective] (Rome, 1583) and, later, by Jean-François Niceron.