Until the end of the 20th century, index cards were the usual form of inventory. For generations, museum staff added information to the stiff paper cards. They added the findings of current research or supplementary information from a wide variety of sources. They also drew sketches on the cards to clarify details that were difficult to see on the object itself. The use of technical innovations such as (colour) photography or typewriters or computers becomes apparent, as well as a steadily growing formalisation of the index card.