Ghost double exposure?

I'm still learning to usemy D7100, and have been trying to do double exposures. The shots come out ok, but in the 2nd shot , the subject looks almost transparent (ghost- like)!!
I set the gain to "on" as advised in the manual, but they all come out the same way!
Does anyone have any advice they can offer on this?

Cheers
Jim

Double exposures are not that simple to do. First, you have to remember that light adds and once you get something white, you can't have anything show over it on your second exposure. So you have to divide your exposure in half,or less for one or the other exposure, making sure that the second image will only show on dark parts of the first, where first and second images could be done reversed with the same result.

It's a little early for me to be thinking this strait.