Wait, I believe I misunderstood you. I thought you wanted pens that you could -cover- with clay and cure. Not pens that would write on polymer clay. If you want pens that -write on- polymer clay, I would think any pen advertised as 'acrylic ink' would be suitable. Sharpie and alcohol based pens look okay when first used, but over time, the ink bleeds into the clay, and the lines get softer and blurrier. There are a few pens that ARE good with polymer, again, checking Blue Bottle Tree, or The Glass Attic would be helpful I'm sure. Colored pencils work on cured clay too - a clay with some texture works better, a very fine texture, like imprinted with silk fabric or a paper towel. Souffle seems to take to colored pencils VERY well, with that suede-like finish.