On most ink bottles a best-before date is printed that is to be understood rather as a minimum-consumption date — the ink is generally still usable afterwards. With normal water-based ink, dried or thickened liquid can be refreshed with distilled water. Iron-gall ink behaves differently: the iron contained oxidises, which permanently impairs the chemical properties and so writing performance. Collectors observe that even very old ink bottles mostly remain usable over decades, provided they are stored tightly closed.