Have you ever had trouble trying to get your mapping pen to work nicely? This is advice from my experience with pens and ink:
I started off with a Pergamano mapping pen. The nibs were a bit scratchy and I found I was putting rather too much ink on the nib, you should only load to the hole in the nib. I have had problems making the ink flow on the parchment, it seems that I couldn't trace without blobs appearing or no ink at all. The answer may be a new nib, the advice is to rinse the new nib carefully in soapy water before you start, also make sure that the white ink is shaken until you hear the ball rattling. With coloured inks just twist them gently to mix.
I have also tried the PCA mapping pen and nibs and have had similar problems, too much or too little ink on the parchment and a scratchy feel to the pen. I have been advised to hold the pen lightly and glide over the parchment keeping the pen as upright as possible and positioned so that you get a very thin line.
I have now tried a Conte mapping pen and so far have not had any problems, the nibs are probably more expensive as you buy them singly, but I suppose that it is worth while if the tracing is smoother and finer and more accurate. Anyone else got any advice?