If you've ever ground whole spices with a mortar and pestle you know it can be tricky—the curved bottom of the mortar can cause the spices to fly out once you start grinding. What's the secret?
It's all about mastering technique, Isolda said in a recent Chowhound discussion. To grind seeds or small-grain spices like fenugreek, begin by tapping lightly to break them up. This can take some time, but it's the only way to keep the contents from flying out of the mortar. Once all the seeds or spices are broken up, you can exert more pressure until they're thoroughly crushed. Incidentally, Isolda prefers a smooth marble mortar and pestle since, unlike wood or porous stone, it doesn't retain smells.
Another option is to rethink your equipment. Chowhound strangemd prefers a Japanese ceramic mortar with textured ribbing, calling it more effective for grinding spices rather than pulverizing them.