The compatibility of Karst Stone Paper with fountain pens can be described as mixed. While the paper is smooth and does not absorb ink as quickly as regular paper, it may cause issues with fountain pens. Some users have reported that fountain pens skip and take a long time to dry on Karst Stone Paper. However, ballpoint pens, gel pens, and pencils work well on the paper. It is important to note that individual experiences may vary, and some fountain pen users might find the paper suitable for their needs.