The first coasters were designed for decanters or wine bottles, so that they could be slid (or "coasted") around the dinner table after the servants had retired.  The Victorians would also use coasters for drinking glasses, these were most commonly made from silver plate or silver plate and wooden bases.
 
Here are a pair of silver plated wine glass coasters with turned oak bases protected by green felt cushions. In good condition.
 
Dimensions: 7.5cm diameter