Fig 1. Light microscopy in action
Our first encounter with animal mummies is with the complete artefact. Photography enables us to record the current appearance of the mummy bundle and assess its level of preservation. Radiography helps us to understand the construction techniques and the animal (or non-animal) remains that each mummy bundle contains. However, this is usually as far as macroscopic techniques can take us. More in-depth information about the materials used to create animal mummies requires microscopic and chemical analysis. And these techniques require samples.
Sampling methods have, in the past, often been highly destructive with large amounts of ‘animal mummy’ required to get meaningful results. This is usually the vision of many museum curatorial and conservation staff when sampling is mentioned, often based on previous experience. Sadly, some museums offered up their finite resource to have no results (or leftover samples) returned to them by the researchers involved. Thus, their caution is understandable.
Fig 2. A feather under microscope transmitted light
Research by The Ancient Egyptian Animal Bio Bank Project is mindful that museums are in a dichotomous position whereby they are responsible both for the preservation and study of their collections. To help them achieve this goal, it is important to follow a protocol which does two things: firstly, only take a sample that does not affect the appearance of the animal mummy (even if that means not sampling at all); and secondly, prioritise non-invasive and non-destructive methods over destructive analysis.
Some animal mummies lend themselves to sampling as they are in a poor state, primarily due to the fact that they are over 2000 years old, have travelled by boat from Egypt and were not always considered valuable artefacts! Samples come in all forms – from linen pieces, feather, fur and bone collected by museums over the years in labelled bags and the ever-present ‘mummy dust’. One problem is that they all seem to look the same! So, first thing is to try to identify what they are and the best non-destructive tool is the light microscope (Fig. 1).
Fig. 3. Feather coated in dense material
The sample is placed on a glass slide to allow it to be viewed under different types of light. Transmitted light (Fig. 2) is useful for samples that were not treated with embalming substances – resins for instance – and are very thin. Those samples which are denser and were covered with mummification ingredients were better suited to reflected light (Fig. 3), which reflects light off the surface of the sample, rather than passing through it.
Reference collections are important for comparison and show us particular characteristics of samples. For instance, feathers are recognisable by their almost leaf-skeleton formation, whereas cat fur has a symmetrical, vertical pattern, a little like a ladder. The flax plant under the light microscope is recognisable by its smooth and flexible appearance and bamboo-like nodes placed at regular intervals along the length of the individual linen strands. These were woven together to make linen for everyday use as clothing and in mummification of humans and animals.
Fig. 4. Tree resin
Some samples are a little trickier; in particular a variety of materials collectively called ‘resins’. A light microscope can say that these substances are present (very important fact!), were hot, thick and sticky when applied to the animal mummy and are thought to originate from tree resins (Fig. 4). However, it cannot identify exactly what the material is. That requires chemical analysis by way of Gas Chromatography-Mass Spectrometry (GC-MS, for short). Each ancient material has an elemental fingerprint, which can be identified by way of a chromatogram, which is a type of print out of the GC-MS result. This graph shows which individual elements are present and in what quantities – almost like a recipe! – helping us to identify the material present.
A collaboration with the University of Bradford has allowed suitable animal mummy samples to be analysed using GC-MS. This has produced interesting results showing the wide use of plant products in animal mummification, including the use of pistacia resin in an ibis mummy in a stone coffin (Fig. 5), tentatively from Saqqara, and the use of pine resins and beeswax in some animal mummies.
Fig. 5. Ibis mummy in stone coffin – courtesy of Durham University Museums
Come and experience some of the sights and smells in our interactive mini-lab in the new exhibition Gifts for the Gods: animal mummies revealed.
 Image courtesy of “Gotaq” by Ailinaleixo – Own work. Licensed under CC BY-SA 3.0 via Commons – https://commons.wikimedia.org/wiki/File:Gotaq.jpg#/media/File:Gotaq.jpg