An ink, first used for writing, made from a suspension of iron-salts in gallic acid obtained from the nutgall, a growth on certain oak trees caused by disease. Originally black, iron-gall ink turns brown with time as the acid eats into the paper with damaging results. Many drawings and manuscripts executed with this ink are, as a result, often extremely fragile. Iron-gall ink was originally used for writing, the first extant examples dating from around ad 200. The earliest iron-gall drawings are from the beginning of the 13th century. Most artists of the early Italian Renaissance employed it for drawing. Many artists of the Baroque era also employed it, such as Rembrandt and his pupils, the Italians Guercino and Pier Francesco Mola, and the Frenchmen Claude Lorrain and Nicolas Poussin. From a later period, much of Van Gogh's correspondence and many of his drawings were also executed with this ink.