Is it possible to darken a pencil drawing to match the colour of charcoal? I am busy sketching the Mona Lisa using pencil and charcoal (unfortunately I cannot add the picture).
I used pencil to do her face and head in the beginning and then used charcoal to start doing the dress. The problem I ran into was that the dress was way darker than the head because of the use ofcharcoal. 

Now I need to make the head darker as well, to match. Is there I way I can do this? Is it even possible? The detail looks just like the original but now the 2 different tones on the artwork make it look pretty crap.
I think that there are a couple of ways of dealing with it.


Rework the head with charcoal, possibly using an eraser and add some pencil marks to the rest so that you have a bit of cohesion everywhere 
Leave the skin as it is (with pencil) and use charcoal everywhere else
Use fixative (or hairspray) to knock back the darkness of the charcoal
Use a mist of white spray paint to subdue everything
Take it in stride as a learning experience and make another drawing