For most of us, the idea of invisible ink has been the stuff of our treasure hunts at the local magic shop and endless childhood wishlists reminiscent of things we saw on Pee Wee's Playhouse. To a group of researchers from Helmholtz-Zentrum Berlin and several Berlin universities, the "invisible ink" of an ancient piece of papyrus from Elephantine Island on the Nile has been all too real, and actively barring Egyptologists from closer examinations of a collection of rare papyri for decades. Utilizing synchrotron radiation from the famous BESSY II, that may be changing.
What is at stake?
Berlin plays home to the Egyptian Museum and Papyrus Collection, a vast cache of often meticulously folded papyri excavated from Elephantine Island by Otto Rubensohn between 1906 and 1908. About 80% or more of these priceless documents have never been studied due to the implicit danger that unfolding a papyrus which has been folded for thousands of years presents to the contents.
It is not simply that the Egyptians intricately folded the papyri, but that they folded them into the most minuscule, tiny sizes imaginable in order to conserve space. The significant aging of these documents disallows unfolding, but also has caused conspicuous blank spots in otherwise character-populous areas on the documents. Check out the symbolic ways that the Egyptians made the papyrus in the following video.
Non-destructive decoding tactics prevail
In order to find out what might have been written on those teasing blank sections, the Berlin physicists have attempted what amounts to an X-ray echo on the papyrus. When the specimen is exposed to X-ray light, the papyrus atoms enter an excitation state and reply with X-ray light of their own making. This general method is referred to as X-ray fluorescence.
Via X-ray fluorescence, the Berlin researchers were able to measure the energy of the radiation returned by the atoms in the papyrus and thus identify them. As Egyptian scribes were known to use some metal-based inks, it was posited that these metals would be visible through X-ray fluorescence if they were, in fact, once used to fill those pesky blank spots. Absorption edge radiography from the Bamline station of BESSY II not only revealed that the invisible ink once there was indeed metal-based but showed the physicists characters in decently high definition.
So, what was the secret message?
The Rathgen Research Laboratory Berlin was able to use a Fourier-transform infrared spectrometer to determine that the ink in the blank boxes was lead carboxylate, which is, interestingly, colorless. The researchers suspect that the vanished characters might originally have been written in coal-black galena (lead glance) or bright minium (red lead).
The chemical reactions instigated by protracted exposure to sunlight would have likely faded these original colors to the mysteriously invisible lead carboxylate version that so beleaguered the curious Egyptologists. No word yet on an official translation, but speculations have been voiced that the characters in the empty spaces represent deities. Not a shocking revelation from the beyonds, but at least a bit more profound than "Be sure to drink your Ovaltine."