I can’t tell you who lent this object to us for scanning but I can tell you that we told no one it was coming. It was with us for just a few hours and none of us were allowed to know where it is normally kept. It is important to be able to identify objects made in this material but many collections that have them are taking them off display.
Why so much secrecy? Guessed what it is?
Yes, it’s rhino horn. The market for this for the Chinese medicine trade is so lucrative that poaching is pushing remaining populations of rhinos to the very brink of extinction (link) and thieves will go to any length to get their hands on natural history specimens or museum objects worked from these horns (link) just to grind them up into powder.
In fact, rhino horn has no proven therapeutic power. It is made from the protein keratin and, apart from a few differences in its amino acid makeup, it is chemically just like cattle horn or horse hoof. Its structure, though, is unique. Cattle, sheep or goat horn is formed in layers over a boney horn core but rhino horn is solid from its base to its tip and is made up from thousands of fine vertical tubules all cemented together. This gives the horn a very fibrous appearance.
3D scanning unworked rhino horn has been a real challenge because of the fine, fibrous texture of the weathered surface, but scanning worked rhino horn has been even more difficult. The sheen on a polished rhino horn cup can create problems for the laser scanning and for the texture photography. Areas of the rhino horn can vary between dark and opaque patches and areas that are quite translucent.
The laser light can penetrate into the translucent areas creating false changes of level in the surface of the 3D model. When the texture photos are taken care has to be taken that supports for the object do not create dark shadows in these translucent areas. On top of this, the translucency and colour varies depending on the angle at which the tubules are viewed and lit. This means that when the object is turned between successive photographs for the texturing, the same area can look darker, lighter or appear to change colour completely.
We’ve overcome some of these problems by carefully diffusing the lighting . If we still have problems then 3D laser scanning is not the answer to producing our 3D photo realistic models, but in these cases we have other techniques to hand. Find out about these techniques in our next update.