To prevent wax bloom, give the drawing a couple of layers of fixative. You may need to wipe off any existing bloom first, if the drawing has taken some time to do. It's important to apply fixative correctly, and to test it before using on finished work. Create a test-piece using the same technique on the same paper, and do a test application to ensure that you are happy with the results.
To remove wax bloom, wipe the surface gently with wad of cotton wool, checking frequently to ensure that you are not moving any pigment. A tissue also works, though can be slightly abrasive. Again, you should practice this method on a practice piece before attempting it on a major work.
