Ink is an organic substance and should not be used for longer than around three years after opening, since oxygen contact, evaporation and ageing change consistency, colour intensity and flow behaviour. Batch-related colour deviations are also normal even with fresh ink. A 1-litre bottle of Montblanc vintage ink from the 1950s is, from a collector view, more likely placed unopened on the shelf as a contemporary witness; collector value drops by opening. Computationally, one litre yields about 20 fillings of today's bottles (shop price about 170 euros); the ink value, however, makes up only a small part of this price; the main share lies in the glass.