FABER-CASTELL PITT ARTIST PENS - Very light-fast and waterproof drawing ink. The quality brush point provides maximum flexibility for spontaneous freehand sketches or accurate detail. Reliable and even flow of ink; point glides softly and smoothly over the paper. Acid free. Highly permanent after drying.

The Blue Bottle Tree review... "Sakura Microperm and PITT Artist Marker both have excellent performance on polymer clay. They both hold up to water and alcohol and neither bleeds when coated with Varathane. Microperm markers can be a bit pale and PITT is probably better if you want a dark line."

Read the whole review at The Blue Bottle Tree