On old writing instruments, ink pigments penetrate the material surface and there form a relatively firm bond with the material that cannot be fully removed either by mere soaking or in the ultrasonic bath. Mechanical work is necessary: collectors use sheet-metal gauges, a scalpel from medical supply or used dentist's instruments from flea markets to clean the channels of the feed cautiously. Before exchanging a feed it should be checked whether an original-faithful replacement is available — not every feed fits mechanically or capillary-technically all models.