Tray of jasper trials, ca. 1773-76, from Josiah Wedgwood's manufacture.

The numbers are keys to the formula, recorded in Wedgwood's "Experiment Book." The letters indicate placement in the kiln and so the firing temperature. Jasperware clays were used for the portrait medallions and ceramic reliefs popular in the late eighteenth century.

Source: Wedgewood Museum, Barlaston, Stoke-on-Trent, England.

Credit: This object is a reproduction of the original in the possession of The Trustees of the Wedgwood Museum. All rights reserved. No reproduction is permitted without express permission of the Trustees.