Color pigment question solved!

Magnified view of 5143 pigment
Magnified view of 5143 pigment in visible light spectrum
IR microscope view of the same section of 5143 pigment
Magnified view of the same image in the infrared light spectrum using IR microscope

Since we started work on the the papyrus 5143c, an open question has been the chemical composition of the pigment used to create the spiral design. The ink on most papyrus fragments has a strong black color indicating the presence of carbon. In contrast, the spiral pigment drawing is brown with a distinct red-orange tone.

Recent analysis using a specially equipped microscope with Infrared (IR) capability confirmed the use of iron-gall ink. Macro images taken in both in the visible and infrared spectrums were compared to each other. In IR iron-gall ink disappears completely. This test confirms that the drawing was made using iron-gall ink. 

Iron gall ink is basically made from powdered gallnuts (gallotannic acid), a metallic salt, gum arabic (a binder), and water resulting in a brown-color. Iron-gall ink is more penetrating, but it also damages the papyrus eventually, a circumstances, that challenges conservators nowadays. The presence of the ink also has implications for exhibition since exposure to light can accelerate loss.

This composition of ink became common practice in Late Antiquity and Middle Ages. We are not sure, when and where its use started. The famous carbonized papyrus-scrolls from Herculaneum, which was destroyed by the eruption of Vesuvius in AD 79, already show traces of metal in the ink:

So far, scholars saw the use of iron gall-ink increasing from the 2nd–3rd century AD

This analysis was carried out by Marieka Kaye, Conservation Librarian, Book Conservator at the University of Michigan. We owe her our thanks!