Fine miniature enamel hand painted portrait 4cms high set in a brass frame 9cms high. During the 19th century, portrait miniatures of John Calvin (1509–1564) experienced a revival in popularity, particularly in Geneva, as part of a renewed interest in the Reformation and its historical figures. These miniatures were often produced to commemorate the Reformation, with this one after artist  Jeanne Henriette Rath 1772-1856. His theological work formed the basis of the Scottish Reformation and the Church of Scotland.  Calvin is often mistaken for a Scottish native due to his monumental impact on the country's religious and cultural identity and here he is in the hat and garb of a Scotsman from the 16th C. 
Henriette Rath a celebrated Swiss woman painter known for her miniature of him and this painted enamel is after her original. I am unsure if it is in her actual hand as it is unsigned. 
The Calvinist form of Protestantism is widely thought to have had a major impact on the formation of the modern world.