
The question of how to keep your gel pens and Pigma or Zig pens from clogging up when you are coloring over other media is one that comes up quite often on the doll lists. I used to have this problem too - now plain old impatience is my biggest problem. The trick to keeping your pens from clogging is to seal each layer before you go on to the next one.
For instance, if you are going to draw the outline of your features with a Pigma pen you should spray it with a fixative before you go on to your other media, especially if it's a wet one such as watercolor pencils. You HAVE to do this if you are using gel pens because they bleed like crazy. I use Krylon Fixative - it stinks so make sure you spray it outside. Let it dry overnight - yes, I know - it's hard - you want to get right into coloring that precious little face. But do it anyway. Then the next day go ahead and do your coloring, if you use gel pen or paint for the whites of the eyes, or for highlights save that till last. Spray again and let dry. Then take your pens and do the final detailing. Do a final seal. For this I like to use Craftgard - which is a waterproof sealer. It goes on kind of oily but dries great and it doesn't change the colors. This lets you clean the doll with a damp washcloth later on in life when she gets a bit dusty.
If your pens have clogged there are a couple of ways to unclog them. One way that was discussed on the lists is to gently draw them along very fine sandpaper and another is to draw them along a paper towel. I often just draw on the back of my hand until it starts to flow again. You'll just have to try them to see what works for you.