Either water or steam is used in the blocking process. Once your mitten is completed, the blocking is done. Blocking will help adjust, and reshape both the length and width of your mitten. Both of your mittens should be identical. Blocking will ensure proper size and fit of your mitten.
Your mitten can be dunked in cool water until completely saturated before shaping. Steam can also be used by pinning the mitten to the correct measurements, then using a steam iron held above the mitten to steam it into shape. Don't let the iron touch your mitten because the natural fibers can be scorched, and man made fibers will be ruined.
Which ever method you decide to use, it is important that the mitten should dry completely.
After blocking your mitten it should still have texture, and life. It should not be blocked to the point where the stitches are lifeless and flat.