Looking for the missing link in the evolution of black inks

In the transition from carbon to iron-gall inks, the two documents from the Egyptian Museum and Papyrus Collection in Berlin
with shelfmarks P 13500 and P 13501 discussed in this work present an important case. Their inks appear brownish, although
they date back to the fourth and third century BCE, when carbon inks are believed to have been commonly if not exclusively
used. Using imaging micro-X-ray fluorescence and infrared reflectography, we discovered that the inks in both documents
contain a significant amount of copper in addition to carbon. Comparing the extant recipes for black writing inks and the
experimental evidence, we suggest that these inks are a transition between the pure carbon and the iron-gall inks. Such inks
may have been quite common before the production of iron-gall ink was clearly understood and established.