Monday, January 23, 2012

What The Bones Know

From the desk 
Conservator at the 
Royal BC Museum
I have been thinking a lot about bones lately having broken the tip off my elbow – lost my funny-bone, so to speak. We also have a lot of bone in the lab at the moment as artifacts are being prepared for inclusion in the new archaeology display.

Through human history, bones have found many uses. Bone meal has long been a staple slow-release fertilizer – ground skeletal material providing the necessary phosphorus for healthy plant growth. Bone china uses up to 50% bone ash to achieve its high levels of whiteness and translucency. Before the widespread availability of metals and, more recently plastics, bone provided a ready source of workable material more finely grained than wood and more resistant to moisture: bone needles, scrapers, combs, buttons, handles for cutlery and tools were created by our resourceful ancestors.

Partially cleaned bone strut of a folding fan. 
The distinctive pattern of blood vessels is clear.
Because we are unaccustomed to thinking of bone as anything other than skeletal material, when found in artifacts it is frequently mis-identified. Ivory, from the teeth of many species, is dense, white and hard; it is very finely grained and has been fashioned into intricate carvings and jewellry. Although bones and teeth are similar chemically, their physical structure reflects their different functions and enables us to identify them. Tiny blood vessels radiate from a bone’s marrow - when bone is carved these vessels mark the surface with tiny dark spots and pits. “French Ivory” is neither ivory nor bone but a marketing name for cellulose nitrate, a plastic widely used in the 1920’s and 30’s. “Vegetable Ivory”, or tagua, is the vegan answer to renewable non-plastics; some palms, especially the Ivory palm of the Andean plains, produce a dense, hard, white nut that can be cut and carved. “Whalebone”, however, is not bone but baleen. Like horn, it is a protein similar to hair and fingernails. Occurring in large sheets in the mouths of filter-feeding whales, it is lightweight, flexible, water-resistant and can be cut and shaped. In the 19th Century, it was the perfect material for “boning” corsets.
Conservator Lisa Bengston 
recording the condition 
of archaeological artifacts

Removed from its damp origin, relieved of its original purpose of holding flesh upright, bone is very susceptible to changes in humidity. Heat or dryness will cause artifacts made of bone to crack and split; once acclimatized, however, they will warp and split if they become wet. Light can raise the temperature as well as causing fading and deterioration. In the museum this means that light sources as well as illumination levels must be carefully chosen; exhibit cases are monitored, and in some instances, buffered with silica gel to maintain a constant level of humidity. To preserve bone artifacts at home, keep them out of direct sunlight and away from the heat of a fireplace or spotlight.

Like ivory, bone is very absorbent. Coloured storage materials can stain bone, as can sulphur containing substances like rubber and wool. Acid-free tissue is an ideal wrap and cushion; excessive acidity can harm the calcium carbonate of which bones are composed, and any fibrous material, including batting or fabric, can catch and tear rough or irregular surfaces. Oils absorbed from handling contribute to a tendency to yellow with age. After many years bone artifacts develop a natural yellowish-brown patina which should be preserved. Light dusting with a soft brush is the safest method of cleaning, though sometimes surface soil can be removed with a barely dampened swab.

 My old bones are pretty fragile, but with the help of some stainless steel screws, will soon be as good as new (I am willing to let the patina take care of itself). The bone artifacts will receive much less invasive brass mounts; stainless steel is expensive and not so easily shaped and welded. Look for the new archaeology exhibit on the third floor. It will be ready this Spring and will include many carefully preserved examples of our ancestors’ ingenuity.

A fractured olecranon is no laughing matter 

1 comment:

  1. Fascinating! :) I hope your elbow heals soon.


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