Durability of the ribbons

We guaranty a usability of at least one year, if the ribbons are stored correctly (temperature 5 to 35 °C, air humidity: 30 to 80%). In fact they are usable for even longer periods of time, even though you cannot be sure that the chemical composition doesn't change when the ribbon is put on stock for a long time. We still have ribbons back from the 80th which still work fine today!