Mark Lewis, Senior Curator of Roman Archaeology and Conservator, National Roman Legion Museum, Caerleon, gave us a fascinating talk on the science of how to conserve archaeological items from the ravages of time, there being four categories of things that can damage an item:

• Chemical
• Biological
• Environmental
• Physical

Environmental can be just the wrong temperature or humidity, or fluctuating temperature & humidity. Too high humidity and mould will grow, too low humidity can cause items to dehydrate and crack. Items in museums are often in glass cases (think green house). Spotlights cause the cases to heat up each day and cool down at night. Ultraviolet or infra-red light damages paper and cloth. These days LED lights are used that don’t cause the heating or produce infra-red damage.

When items are first excavated they are often wet. Wet wood is freeze dried to expel the water, then the water is replaced with polyethylene glycol. When wet rocks or pottery dry out, salts in them will crystallise out, and can either come to the surface and just be brushed off, or they can come out to just below the surface which will cause the surface to flake off. So the items need to be desalinated before they are dried out.

Chemical damage can come from acidic human grease from handling, contaminants from the soil the item was buried in, or old conservation techniques (that we now know cause damage). When an item is dug out of the ground, it is suddenly exposed to air and oxidation starts. When copper, brass and iron items oxides them break down (think rust), so items need to be treated quickly.

A lacquer made from cashew nuts is now used to as a glue for wood and ceramics, and as a protective coating as it is waterproof and has antiseptic properties.

Biological threats include wood worm, carpet moth and the like. Physical threats include being dropped or lost, or just lost knowledge of where they are!

Mark’s talk also included forensic archaeological uses for x-Ray Diffraction, x-Ray Florescence, Fourier Transform Infrared Spectroscopy, and some wonderfully simple ways to see beneath the ground: magnetometers and LIDAR can be used to look into the ground without actually digging it up, and strontium analysis of tooth enamel can be used to work out where someone grew up.

Wendy Lefevre

Image © Amgueddfa Cymru-National Museum Wales