Is this ivory? Or china?
The material itself is a type of ceramic known as stoneware which isn't quite as fine as china. This style of stoneware--white on a colored background--was developed by Wedgwood and is known as Jasperware.
The term Jasperware comes from what the Wedgwood artists were trying to imitate: ancient Roman pieces of jasper decorated with white figures. All of the clay starts out white and is then coated in a proprietary slip including very finely ground pigments.