I use Staedtler pigment liner Sketch Pens. They come 4 to a pack. .1mm .3mm .5mm .7mm I have 1 set now for three years. They "erase" with alcohol and I dust the new lines with clear dope with my airbrush to seal the lines. They only cost me $10.
http://www.dickblick.com/zz207/57/
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Also...remember whether or not you use those new pens....THINK CLEAN CLEAN CLEAN...as the surface must be free of all finger prints. Although I don't advocate some harse cleaners such as Prep-sol and Naptha. I have had good results using my rapid-o-graph pens with the "etch" formula that seems to work ever so beautifully and can be cleaned with a watered down soft paper towel wetted with "Earth friendly-No Chlorine, Perfume or Dye...Hasn't scratched yet..over 120 years
BON AMI POLISHING CLEANSER. seems to work amazingly well for me over the years.
Plus it rinses clean, clean, clean with no residue. Remember that sooooo many cleaners "scratch dirt and fingerprints away...Bon Ami's soft abrasives are unique.
Try it.....we used this in the wind tunnel for many projects that we could not use Naptha or Prep-sol based cleaners???