I have been doing fan cels for about a year now 
and have only used one kind of pen the whole 
time. I only use DecoColor Extra-Fine tips. I 
draw on the back with the paint pen then paint 
over the lines. I have never had any trouble with 
these pens. Like Requiem stated be careful not to 
smudge. I usually throw away the cel if I smodge 
it but now I will have to try out Requiem's 
suggestion. So i'm excited now. Thanks.
Alita