 With a material dry, you can clean the dormant powdery mold. One effective way is by vacuuming using a HEPA filter vacuum. This is a machine with a special filter that traps dirt, dust, and mold particles inside it, preventing them from being exhausted back out into the air. You may need to use a screen so that you're vacuuming through the screen, or you may want to be putting cheese cloth between the end of the hose and the vacuum attachment so that you're not risking the possibility of a piece of the artifact going with the debris that is going into the vacuum cleaner.