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Red Casein Loaner Pen - Sheaffer tried using Casein plastics in the early 1920's. The material is not stable and it shrinks or expands as the temperature and humidity change. This unfortunately allows the section to fall  out of the pen. Since this was not a good selling point the pens were used as loaners. They are marked on the side "Service Pen Loaned By" and below that is the name of the pen repair shop. This one is from Stecker's Book Store. These pens should not be soaked in water. It can cause perminat damage!!!