This is a very large example of an Arts & Crafts “Ruskin” brooch, so called after brooches of the same type popularized by Ruskin Pottery.
Dating to about 1900, it has an unusually large glazed art pottery cabochon (or “plaque”) of foamy sea green with hints of turquoise and soft russet marbling. On close inspection the colouring is complex with light crazing – typical of Ruskin-type glazes.
The plaque is set in a pewter mount textured with a petal-like design. The pewter folds over the edges of a base metal backplate, most likely brass, fitted with a simple period c-clasp.
It is 5.8 cm (2.25″) in diameter.
No maker’s or other marks.
Very good antique condition.
There is no damage to the art pottery plaque. The pewter mount is slightly raised up in one place, slightly noticeable on a side view only. There’s also a fold in the rim holding the plaque but I believe this is an original flaw – just the way it was made. The c-clasp does not have very much of a curl to it but holds the pin stem securely enough when worn.
To learn more about Ruskins, this wonderful article – Ruskins: Wearable Jewels of the Arts & Crafts Movement – provides detailed information with photographs, and is a pleasure to read.