The Geha cartridges sold by Pelikan today no longer fit into old Geha cartridge pens, and converters have not been produced for more than ten years. Without an old original cartridge from which a makeshift converter could be tinkered, such a pen practically remains a display piece only. The problem is not limited to Geha: even big brands like Waterman have changed their cartridge system and gradually discontinue supply with converters and cartridges of older models. Polyethylene, the material of the old cartridges, cannot reliably be glued, which makes self-build difficult. The case illustrates the general risk of proprietary filling or consumable systems.