Toadstone ring – sympathetic magic
William Shakespeare referred to toadstones in As You Like It :
Sweet are the uses of adversity,
Which, like the toad, ugly and venomous,
Wears yet a precious jewel in his head.
A rare toadstone and silver ring ring, circa 1680 – 1700. Toadstone is an amuletic ‘stone’ which was highly prized for its magical powers. Toadstones were considered an antidote to poison and thought to sweat when they came close to a toxic substance, as described in 1569 by Edward Fenton: Being used in rings they give forewarning of venom. As toads were thought to secrete toxins, toadstones were believed to use sympathetic magic to cure those who had been poisoned. Mothers wore toadstones to protect their children from being swapped for changelings by fairies.
In folklore, a toadstone had to be removed from a toad while the creature was still alive to retain its magical power. Topsell  gave instructions on how to remove the stone from a live toad, by placing it on a red cloth and waiting for it to belch out the toadstone. He advised that it should quickly be stored away before the toad seeks to take it back. Lupton  suggested an equally imaginative way to extract the jewel: ‘ Put a great or overgrowne Tode… into an earthen pot, and put the same in an Ants hillocke, and cover the same with Earth, which Toade at length the Ants will eate. So that the bones of the Toade and stone will be left in the Pot’.
Toadstones are actually the fossilized teeth of Lepidotus, an extinct genus of ray-finned fish from the Jurassic period. The ring is size T [US 6 and 1/2] and the toadstone measures 1/3 of an inch by 1/3 of an inch. Similar examples of toadstone rings can be found in the collections of the British Museum, the Victoria and Albert Museum, the Museum of London (as part of the Cheapside Hoard), the Ashmolean Museum and the Metropolitan Museum of Art in New York.
Extracting a toadstone from a toad
A jeweller setting a toadstone to a ring
similar toadstone ring in the British Museum