Centuries ago medieval monks typically used iron gall ink to copy texts onto parchments made from sheepskin or cowhide. Unfortunately these documents grew harder and harder to read over time, in part because the ink would fade from a dark black to a light brown; the parchment slowly darkened as well. The contrast that was once stark slowly grew distorted, often rendering the texts illegible.

Making matters worse, parchment became incredibly expensive during the Middle Ages. Rather than go to the trouble of creating new material by scraping animal skin and curing it, monks often reused older parchments containing texts that they no longer valued. They would scrape off as much of the old ink as possible, rotate the page 90 degrees, and then write a new text across it. As a result, the original content on countless manuscripts has remained a mystery.

For decades researchers have used ultraviolet light to resurrect these lost texts. This process works because the collagen in the parchment fluoresces a soft blue color under near-ultraviolet illumination. The ink, however, strongly absorbs the near-UV light, which transforms the faded light brown ink to appear black again, restoring the contrast that once existed.

An overwritten manuscript, purchased on eBay, under normal light. Credit: Shawn O'Bryhim
The same manuscript, under UV light. Credit: Shawn O'Bryhim

Unfortunately, the modern devices employed for this purpose are far too large for researchers to carry with them as they travel around the world and are too expensive for archives and libraries to purchase. Therefore, the equipment must either be shipped at great cost or the documents must be removed from their permanent homes to the nearest device. This can be incredibly burdensome and risks damaging the already fragile texts.

Removing this unnecessary step is what drove us to work together to create the “Manuscript Illuminator,” a lightweight, low cost and, most importantly, portable device that researchers can use to reveal and record texts that have been lost for centuries.

Over the course of about two years we performed several laboratory experiments on various manuscripts that pinpointed the optimum wavelength and bandwidth of the UV light at between 365 and 390 nanometers, just outside the range that our eyes normally detect. These wavelengths can be produced by LEDs, and they make the parchment fluoresce around 420 to 460 nanometers—a range that is easily detected and recorded by standard digital cameras.

In December 2015 the Illuminator was placed into a small suitcase and sent to the manuscript library of Ruprecht-Karls University of Heidelberg. A section of one of its manuscripts had been scraped off and written over. Another researcher had already examined it and made an educated guess as to the obscured reading. After just a few seconds under the Manuscript Illuminator, his hypothesis had been definitively confirmed.

The Manuscript Illuminator is far more portable and less expensive than comparable devices. Credit: Franklin & Marshall College Office of Communications/Deb Grove

Not including labor, the cost in materials to develop the device was $500, which largely covered a lithium battery to provide an independent power source. If manufactured, we would want to ensure the price remained in reach for researchers who might benefit from its accessibility.

It remains to be seen whether scholars of ancient texts will flock to the archives with this new tool in hand, but the goal is not for the singular groundbreaking discovery of a lost document. Instead, the gradual deciphering of materials over time will continue to advance our knowledge and understanding of these problematic manuscripts. If our medieval predecessors felt it important enough to create and save these texts centuries ago, there’s no telling what discoveries could be revealed under the light of the Manuscript Illuminator.