Pearl durability
Pearl durability
Hi Marebear,
With pearls you have a double-edged sword. You have to wear them or they dry out and the nacre goes dull and crumbly (happens to opals, too, but that's a different story). If you wear them the nacre slowly erodes. Now that the nacre is usually very thin in akoyas they wear off a lot faster than in the olden days.
For instance, bleach destroys protein in a process called denaturization. That makes pearls whiter and also more glossy because the conchiolin (the protein that glues the aragonite crystals that form the nacre together) is both inherently colored and more or less opaque. So, if you dunk your pearls in bleach they become whiter and have greater potential for a nacre quality called "water" that refers to the nacre's transparency. However, this process also destroys the very stuff that holds the nacre together. As a result the nacre gets more brittle and abrades more easily because there is less or even no conchiolin to provide cohesion and elasticity.
The extra water however comes at the price of losing another quality of luster called "mirror" that refers to the reflectivity of the nacre. The conchiolin's inherent body color (ranging from greyish blue to greenish brown) originally provided the mirror backing just like with your mirror at home. If you take the silvery black coating away, the glass is by far not as reflective as the mirror was.
The next processing step is thus to put some color back in but one that is a) desirable (i.e. pink) and b) transparent so as to not interfer with water. Then of course, you are still short of reflective backing so pearl processors buff the pearls with wax and some of them even coat the surface of the pearls with a metal vapor deposition. Rhodium vapor deposition tends to produce the most desirable color of a pinkish lavender with a touch of metallic bling. In the olden days, pearl farmers would have to selectively breed albino mussels (they are not oysters) because their conchiolin is transparent pink to achieve the same effect. Modern chemistry allows us to have the same look without the effort of selective breeding and the risks of long culturing times.
And, of course there is no orient (the rainbow play of color that is a function of light being reflected through a substantial layer of nacre) in such pearls.
Was that short enough?
Zeide