Drawing Techniques: a Guide
Brown inks : Iron-Gall Ink  

Old Master drawings are popularly identified with the handsome brown color of their ink. Formerly these sheets were commonly described with the misnomer "sepia". It is usual today to describe all such drawings as "pen and brown ink" or "brush and brown wash", because, although a number of different inks were used, it is difficult to distinguish between them. Of the two primary kinds of ink, bistre presents more or less the original appearance at the time of use, and iron-gall ink turns from black to brown with time.

Iron-gall ink, the most common ink used before the nineteenth century, both for writing and for drawing, was made from a concoction of iron sulfate, gall-nuts, and gum arabic, which was added as a binder. Iron-gall ink may be somewhat less transparent, but is only very obviously distinguishable from bistre when it has been applied in excessive concentration. In these cases, the acidity of the ink eats through the paper to the severe detriment of the artwork. Curiously it was this quality which first attracted scribes to iron-gall ink in the middle ages. It became invaluable for drafting legal documents, since, once it began to eat through the paper fibers, it could not be erased or blurred by scraping or washing.

Link: The Iron-gall Ink Corrosion Web Site [http://www.knaw.nl/ecpa/ink/]

  Pierfrancesco Mola. Caricature. National Gallery of Art, Washington, D.C.