Hi John None that I know of, but note... When I have used it to label bags or bottles (plastic or glass) 1) the surface needs to be clean & oil free. 2) If it comes in contact with alcohol such as: Ethanol, Isopropanol, Glycol, Ethylene Glycol, it tends to run, or become non-adherent and wipe off. So this fact probably applies to shells as well. I do find it great for labels! I recomend using the Sanford Brand Sharpie - Ultra Fine Point - Series 37000 Leslie ---------------------------------- Is there any good reason not to use Sharpie permanent marker pens on shells? (It is a US brand of permanent marker pens which are much easier to use than India ink) Thanks for any info. John Wolff Lancaster, PA