Mortar and Pestles
It's a good idea to have two - or even more, depending on how you plan to use them. If you make guacamole and salsa, you might want a separate mortar and pestle so that the stronger herbs and seeds you grind won't flavour these more delicate dishes in an odd way.
How to Season a New Mortar and Pestle
The next thing I learned is that a new mortar and pestle must be seasoned, like a new cast iron pan needs to be seasoned. The actual process is different but they both need to be prepared before they are used for the first time.
A new mortar and pestle set needs to be seasoned to remove stone grit from the inside. The interior surface is left rough and unpolished so the items you're grinding can "grab" the bottom and sides and not jump out of the bowl. Without seasoning it first, you'll end up with sand or grit in your food.
First wash the mortar with hot water and let it air dry. Never use soap or it will flavor your food. Then grind a small handful of uncooked white rice with a bit of water. You'll need to do this several times, until the rice powder is "clean" and has no grit or color in it.
After rinsing out the rice, grind a whole clove of garlic with a teaspoon of salt, another of sugar, and a few peppercorns. Mash this into a smooth paste and rub it around the inside of the mortar. Let it set for about thirty minutes, then wash it with hot water (Do not use soap, or it will flavour your food) and let it air dry. Your mortar and pestle are now ready to use.
Cleaning
Wash the mortar and pestle in hot water and air dry immediately after use to minimize staining. Granite is especially prone to staining when exposed to acidic and oily foods.