Schreger Lines and Narwhal Tusks

On Tuesday and Wednesday I attended a course at Lancashire Conservation Studios on how to identify keratinous and osseous materials. The course (which was taught by Dr. Sonia O’ Connor) was so intensive that I couldn’t possibly touch on everything we covered in one blog post, but here are a few of the things we learnt.

The first lectures were on how to tell the basic differences between antler and bone. One of the most basic ways to tell via a cross section is that longbones have a hollow cavity where the bone marrow once sat, and antler has a spongy material all the way through it. Of course, this becomes harder to discern when the bone or antler is fashioned into an object, or the spongy material in the middle of the antler is removed.

After a coffee break and getting to know each other, we learnt about our next material: Ivory. Ivory is a word used to describe any animal material which is dentine in origin. The most well known ivory is that of elephant. However, many people have trouble identifying it.

If the ivory has been fashioned into an object, has been broken or cut down the middle, then sometimes a pattern called Schreger can be spotted. Schreger pattern is made up of intersecting lines that change in colour when hit by light. They appear at convex and concave angles.

Below is a broken piece of elephant ivory displaying this pattern.

In elephants, the angle Schreger patterns is obtuse, while in mammoths and other extinct Proboscideans the angles are acute.

Cross-section of elephant ivory:

Cross-section of mammoth ivory:

Schreger lines won’t be of much help if you have an intact elephant tusk, however. Elephant tusks are often confused with the incisors of hippos. They are similar in shape, and in younger elephants, also in size. There are differences that can point to clues though. Elephant tusks tend to be more oval in shape, while hippos are much more round. Hippo tusks are also bent at more of an angle, and have an inner commisure.

Hippo tooth:

Crocodile carved from hippo tooth. Note the lack of Schreger pattern throughout:

Sonia also showed us other forms of ivory such as sperm whale teeth, walrus tusks and this impressive Narwhal tusk:

We also had a lecture on other organic substances, for example whale balleen, which was used in the past to shape corsets and other articles of clothing. Tortoiseshell, vegetable ivory, hornbill casques were also discussed.

On the second day, we were given a practical. We were split into groups of two and each of us was given a tray of items and a microscope. Using the information we learnt and the microscope, we has to discern what each object was. A task that was not as easy when the animal substances were fashioned by people into objects!