Parchment Browning–part II: The Dead Sea Scrolls

https://doi.org/10.1016/j.polymdegradstab.2020.109414Get rights and content

Highlights

  • Large parts of the Dead Sea scrolls' (DSS) text is obscured by parchment darkening.

  • Checking theory on parchment and collagen browning developed in 'part I' on the DSS.

  • Comparing 2000 years of natural aging vs. artificial aging of parchment.

  • Browning could be due prolonged water exposure, ex. slowly evaporating salt water.

  • Pigments are likely melanoidins formed via Maillard reaction.

Abstract

The Dead Sea Scrolls are often described as the most important archaeological find of the 20th century. These 2000 years old manuscripts have great religious, historical and linguistic importance. The fact that large parts of these texts are obscured by the darkening of the parchment is extremely unfortunate. In our previous research we explored the possible causes of parchment browning or darkening using artificial aging, which allowed both destructive and non-destructive testing. Our results could be summarized as two main theories, one related to parchment fibers flattening and changing the way light is reflected, the second related to the formation of strong brown pigments, likely from the melanoidin family. Here we examine the scrolls themselves and discuss their degradation in light of these theories. The main DSS collection could only be surveyed by completely non-destructive means, namely multispectral imaging and Diffuse Reflected Infrared Fourier Transform (DRIFT); however, a few fragments were examined by micro-destructive means including SEM and FTIR-ATR and EPR. Despite the great variation between scrolls, we demonstrate that the browning of the scrolls and their degradation fits within the framework of those theories developed on artificially aged samples. We suggest the extreme degradation occurred when parchment was exposed to water and particularly if that water was slow to evaporate, for example saturated salt water which is slow to evaporate, and was very likely present in the caves where the scrolls were found by the Dead Sea. Hydrolysis and denaturation freed the necessary components to meet and initiate the formation of large melanoidins.

Introduction

The Dead Sea Scrolls (DSS) were first discovered in a cave in the Judean Desert on the northwestern shore of the Dead Sea. The majority date to the 1st century BCE-70 CE and include religious texts written at a time when both Judaism and Christianity were being formalized to the religions we know today [1], [2], [3]. Once the importance of the documents had been established, the caves in that area were surveyed, excavated and at times unfortunately looted. Over 25,000 DSS fragments belonging to about 1000 manuscripts were unearthed [4].

The state of preservation of the DSS is amazing considering their age (Fig. 1); however, many of the fragments are badly damaged. The parchment has in some cases turned so dark that the contrast with the ink was lost and the text can only be read using near infra-red (NIR) light. Photographs of the scrolls from the 1950s show much of the damage was already present at that time of their discovery. The scholars who took charge of the DSS at that point applied various materials to the DSS in attempts to unroll, soften and improve the legibility. Also various types of tape and glue were used to attach fragments. Some of these treatments caused additional harm. More detail on this has been published previously [5].

Parchment, the substrate of most of the scrolls, has been in use since 2500 BC as indicated by drawings in Egyptian tombs [6]. It is made from animal skins, usually goat, sheep or calf. There is no known description of the methods of parchment manufacture at the time the DSS were written. Modern parchment is produced by similar methods to those documented in the Middle Ages in Europe: Hides are cured in salt then soaked in a lime bath (CaO), after which flesh and hair can be easily removed leaving only skin, the skin is then stretched on a frame to dry. The skin may be smoothed using a pumice stone, or chalk can be rubbed into the surface to whiten the parchment. Some modern manufacturers add enzymes to the parchment after the lime bath to soften the parchment. Historically this was accomplished using animal excrements or rotten vegetable matter. Parchment prepared according to Jewish tradition is somewhat different. The Rambam, who wrote about Jewish practices and laws in the 12th century, mentions an additional step using flour to treat the skin. The term ‘flour’ is interpreted broadly and more frequently ground barley is used. Possibly this serves as a source of enzymes for softening the parchment. The Rambam also explains the final step for Jewish parchment preparation, which is lightly tanning the skin, using vegetable tannins [7,8]. Earlier studies of the DSS confirmed the presence of tannins, sometimes throughout the parchment and sometimes focused on the hair side, which was prepared for writing [9].

Earlier we used modern parchment, prepared by such traditional methods (using barley as flour), for a series of artificial aging experiments [10]. We studied the change in color as well as changes to the chemistry and structure of the parchment. The main component of parchment is collagen, a protein that has been studied extensively. The main degradation pathways are hydrolysis, oxidation and denaturation [11]. To summarize our results, we found with exposure to heat and humidity the parchment underwent some hydrolysis and denaturation, and also some browning. Extreme darkening of the parchment, as seen on some DSS, only happened with exposure to water, particularly if the water was not allowed to evaporate quickly. This sort of damage was associated with total loss of structure in the collagen. We theorized that the flattening of the translucent fibers could be contributing to an apparent change in color. However, following additional analysis of artificially aged parchment we believe the main reason for browning was formation of pigments, most likely melanoidins. These are loosely defined as large, brown, N-containing macromolecules formed by Maillard reaction between amino-acids and reducing sugars or oxidized lipids. These are strong enough pigments that even when formed in such small quantities that are difficult to detect analytically, they can still cause a drastic color change. In parchment the source for amino-acids is obviously the degrading collagen. The source of reducing sugars may be less obvious. Skin does contain proteoglycans and other forms of sugar, but most of that is presumed to wash out during the parchment preparation. It is possible enough remains to react and form pigments. Additionally, the barley-flour used and the plant extracts used for tanning the parchment are potential sources for more sugars. Wallert and Schilling found polysaccharides in DSS cross-sections [12], proving the necessary components exist for our theorized browning mechanism. Alternatively, Zamora & Hidalgo have suggested that oxidized lipids (which are definitely present in parchment and the DSS [5]) could react along with sugars, or even in place of them, to initiate the melanoidin formation mechanism [13].

So far, we have mainly addressed results of artificially aged parchment; however, the only way to fully recreate the effects of 2000 years of natural aging is to wait 2000 years. It was necessary to examine actual scrolls, to see which of our observations from the artificial aging are repeated in the scrolls themselves. There are two main issues with this: first, the majority of the scroll collection cannot be examined by any destructive means. Only four small fragments, with no writing or assignment to a particular manuscript, were made available for more extensive analysis. Second, the preliminary results from those 4 fragments, as well as earlier studies on the scrolls [9], showed great variation between scrolls. Differences are due to the original manufacturing (ex. different types of tannins, different quantities of calcium carbonate), differences in storage conditions (ex. found buried in mud vs. wrapped in linen, found in a bat cave or one inaccessible to most wildlife), and finally differences in treatments after discovery including unrecorded interventions by the first scroll scholars and various conservation efforts. Despite all these differences, we found that the basic degradation chemistry and browning mechanism appear to be consistent and only vary to an extent with the specific conditions for each fragment.

Section snippets

Samples

DSS samples were provided by the Scrolls Conservation Lab of the Israel Antiquities Authority (IAA). Only four small fragments, with no writing or association with a particular manuscript, were subjected to extensive analysis. Other DSS were examined in the conservation lab by un-invasive means.

For artificially aged parchment, full details were provided in our previous paper [10], briefly:

Cycle A: Pieces of traditionally prepared parchment were placed in an artificial aging chamber maintained

FTIR-ATR

The theories we developed and mentioned in the introduction were all based on artificially aged modern parchment. The first question, therefore has to be, how similar was our modern parchment to the DSS? Fig. 2 shows an FTIR-ATR comparison of our artificially aged parchment and a DSS fragment (both darkened extremely). While there are differences in relative peak sizes, the actual peak locations are almost identical in both parchments. This proves that our suppositions about parchment

Conclusions

The theories regarding the parchment browning established based on artificial aging experiments, discussed in our previous paper, were put to test by comparison to analysis of original DSS fragments. We found that artificial aging was successful in recreating some aspects of the DSS degradation, especially in the case of parchment artificially aged while damp. Both the chemistry (as seen in FTIR) and the structure were almost identical to a DSS fragment of similar appearance. In cases of less

Authors' contribution

Yonah Maor: designed experiments with advice from ZA, conducted the experiments, analyzed the data and wrote the papers;

Pnina Shor and Zeev Aizenshtat: advised, supervised and reviewed the paper.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors would like to thank the DSS unit team: Lena Libman, Tanya Bitler, Tanya Treiger, Yana Frumkin, Shai Halevi, Orit Rosengarten, Beatriz Riestra and Ilit Cohen-Ofri, for providing samples, discussing their conditions, photographing samples and much more. We also thank the scientists who provided access and assistance to the various analytical methods used: Amram Samuni, Marcello Manfredi and the staff of the Hebrew University nano center. Yonah Maor also thanks the institutes that

References (22)

  • J.B. Poole

    The Nature, Origins and Techniques of Manufacture of those of the Dead Sea Scrolls which are made from Animal Skins

    (1960)
  • View full text