The effect of making the image of a chosen card appear in the gemstone of the magician's ring is described by Edmé-Gilles Guyot in Nouvelles récréations physiques et mathématiques, Vol. 2, p. 287; p. 35 of Jean Hugard's unpublished translation. A card is forced, then burnt. The spectator looks into the gemstone on the performer's ring and sees nothing unusual. The performer then rubs ashes from the burnt card onto the stone (secretly revolving the ring on his finger to bring a duplicate bezel and stone into view), and the spectator now sees his card in the stone.

Guyot also describes a second type of gimmicked finger ring for this effect. Instead of having two bezels mounted opposite each other on the ring, there is only one. This bezel can be shifted slightly to hide or display an image of the tiny card resting in a small compartment under the stone.