A completely solvent-free ink does not in principle exist, since water itself is an inorganic solvent; the claim that Pelikan ink, in contrast to MB ink, is gentler on historical pens is not substantiated. Recommended for old pens is Pelikan 4001 royal blue or Montblanc royal blue, both well water-soluble and so easily rinsed from the feed. In general, caution is warranted with coloured and especially red inks, since they are more aggressive and can eat into the material. Iron-gall ink should absolutely be avoided in old pens. Ink can indeed spoil or grow mould, which is why use of ink no older than three years and regular cleaning of pens is recommended. Open shelf life is, according to Pelikan, about five years for ink bottles and twelve months for cartridges.