BEAL has developed a special ink for marking ropes, in the middle as well as at the ends. This ink hardly stiffens the rope, is water resistant, and stands up to abrasion well. There is a small roller at the tip for better inking, and you can make 30 marks of 5cm from just one container.

Features
• Water Resistant
• Durable
• Warranty – Depends on end use
Design
• Hypoallergenic
• Excellent hold
• Very good abrasion resistance
• 30x 5cm rope marks from one container

https://www.alpinesavvy.com/blog/how-to-use-the-beal-rope-marker