Preparing dried chilies

Preparing dried chilies 
in general, large, smooth chilies are much less hot
than small, wrinkly chilies. Both are used dried and
fresh. When dried, chilies are normally rehydrated
before adding to a recipe. They may be seeded, too,
to make them less hot. When preparing chilies, you
may want to wear plastic or rubber gloves, as there
is an alkaloid in chilies, called capsaicin, that can
irritate your skin. After preparing chilies, thoroughly
wash your hands with soapy water .
Put the chilies in a bowl of lukewarm water and place a small plate on top to keep them submerged. Leave to soak until soft and fully rehydrated (this can take as long as 15–30 minutes, depending on the size of the chilies).
Drain the chilies and pat dry with paper towels. Tear the chilies open and remove the stalks, veins, and seeds. (It is the seeds and veins in a chili that contain the heat.) Chop the chilies, then grind in a mortar for a curry paste or use according to the recipe instructions.
Ground roasted chilies
Roast dried chilies (mildly hot red chilies or very hot bird’s-eye or bird
chilies) in a wok or pan over moderate heat, stirring regularly to
prevent scorching, until they change color and smell toasted. Allow to
cool, then grind to a coarse or fine powder with a mortar and pestle,
a clean coffee grinder, or a spice mill. The powder will keep well in an
airtight container in a dark, cool place for up to 1 year.