Iron-gall inks leave waterproof deposits, which is particularly problematic on old pens and rare use; a 342 can in an emergency be opened and cleaned, but regular use is not recommended. Practical experience shows that even with weekly cleaning, traces can arise on the ink window and in the feed. Frequent flushing with lukewarm (not hot) water is recommended by drawing in and emptying until the rinsing is clear. Anyone using iron-gall ink anyway should use the pen daily and care for it thoroughly; in doubt a modern water-soluble ink is safer for valuable vintage pieces.