Metamorphosis implies change. Sometimes the change is simply from one thing to another, and with art that frequently meant using a flap, or an overlay. Sometimes the change is more subtle and more mysterious and refers to something being hidden or disguised
One has to look no further than nature to see hidden images, and to appreciate how compelling they are. Occasionally when we look at a rock or a tree we see something else, the shape of a familiar figure, or perhaps the profile of a face. Artists in the 17th century pushed this idea of nature hiding images and created anthropomorphic art. There is a famous anthropomorphic image in Kircherís Ars Magia lucis et umbrae and a wonderful series of anthropomorphic images called The Four Seasons by the German artist Johannn Matrin Will (c. 1780).
Another type of hidden images are turning heads. Some of the earliest of these, 16th. century pieces, were both political and highly satirical, and one of the favorite subjects for such satirical treatment were leaders of the Catholic Church. Theodor de Bryís 1558 Conceit and Insanity produced a turning head with one face being that of the pope and the other the devil or a fool. This image was widely replicated.
The political figures and nobility of the day often turned up as hidden images in works of art, often seen in the white space between trees, in tree branches and on the borders of vases. Napoleonís form was one of the most popular and was frequently hidden in an otherwise innocuous scene.
The variety of metamorphic toys is nearly endless. Some are very well known, such as the kaleidescope invented by Sir David Brewster in 1816, a toy that remains popular today. The kaleidescope uses mirrors to create endless, changing patterns. The tricenium, known today as the three way picture, allows three different images to be viewed depending on how a viewer moves in front of the image. The earliest type of moveable book, the Harlinquenade, is a metamorphic toy which illustrates a story and then when opened up the pieces reform to create more of the same story or another story. Finally, one of the most popular Victorian toys was the metamorphic puzzle which allowed an endless number of faces and forms to be made from dissected pieces.