Jasperware was matte finish pottery product (some refer to it as porcelain) developed by Josiah Wedgwood and used to imitate onyx or sardonyx in that it had a background color (usually blue, but not always) with the white design in relief.

Jasperware Cameo.jpg
Wedgewood Mark.jpg

Example of the Wedgewood Mark - 1908 to 1969.

Date Jasperware Markings
Prior to 1860 Wedgewood
1860 - 1891 Three Letters: Month, Potter, Year
1891 - 1908 Wedgewood
(stamped separately)
1908 - 1969 Wedgewood
  Made in England
(stamped separately)
1970 - Present Wedgewood Made in England

Jasperware Web Site