2007: I stumbled upon this article during my research. It's an excellent article on cosmetics and the after-effects on pearls and other gem materials.
(via The Journal of Gemmology, Vol. IX, No.8, October 1964) R Webster writes:
Little has been recorded in literature of the possible effects on certain types of gem materials and pearls by the action of cosmetics used in beauty treatments, despite the fact that the embellishment of the natural appearance of women, and men, by the application of various preparations of mineral, animal and vegetable nature have been used since prehistoric times. The extensive use of the modern artificially made products used in beauty treatments today makes consideration of their effects of some importance.
It is quite clear that no harm will come to those gemstones cut from single crystals, except the greasy components of some cosmetics may adhere to the setting and backs of the stones causing them to lose their brilliancy. This, of course, is most important with diamond, a stone which collects grease so readily, and whose optical properties depend so much on the total internal reflection of light from the rear facets. Periodical cleaning is the answer here, and as this should be done anyway, there is no problem.
Those gem materials which are to some extent porous (and, indeed, these are the gems which can be artificially colored by stain or dye) are obviously those most likely to be adversely affected by the haphazard use of various cosmetic preparations. The most important of such gems are pearl, turquoise, opal and jade, and possibly agate and coral. Pearls are the most likely to suffer damage owing to the nature of their structure and to the fact that in the case of necklets especially, and to some extent earrings, they, when worn lie close to the skin or hair.
When it is realized that cosmetic preparations cover such fields as hair dyes and bleaches, depilatories, skin creams and face powders, hair-setting lotions and sprays, as well as eye shadow, lipstick and nail varnishes, and that each manufacturer has a different formula for his various products, it is obvious that any complete investigation would need the full time services of several workers. This, from economic considerations alone, would be out of the question. Some experiments and some actual cases which have been investigated and which have been reported from other workers are here recorded.
Pearls
Experience has shown that there are two distinct ways in which cosmetics can affect pearls. These are surface contamination and contamination which has worked inwardly through the string canal.
Surface contamination mostly occurs through the use of hair-setting sprays, perspiration deodorant sprays, and atomized perfumes. Hair-setting sprays often contain a synthetic cellulose derivative, such as methyl cellulose, and this, if used when pearls are worn, may give a coating of lacquer to them. Such an accidental lacquering, as has been shown by experiment, so coats the pearls that a pin drawn across the surface will dig up this coating in a similar manner to the effect shown when a pin is pressed against a solid glass type imitation pearl. Further, this coating tends to mask the suture marks, that is the overlapping edges of the aragonite platelets, and this also tends to give the impression that one is dealing with an imitation pearl.
When this extraneous coating ages, or has collected on the pearls rather as droplets than as a complete covering, the coating may peel or flake off and give the impression that it is the pearls that are flaking away. It is well for the jeweler to be mindful of this, as it has not been unknown for a customer to complain of this flaking of her pearls.
The second type of contamination, inwardly, may be illustrated by an actual case where an investigation was carried out. Briefly, a cultured pearl necklet was restrung by a jeweler on behalf of a customer and after about three months had elapsed the lady brought the necklet back and complained that since the pearls had been restrung a number of pearls had turned to a blackish color. The jeweler’s assistant who saw the lady fully agreed that some of the pearls had blackened and asked her to call again and discuss the matter with the manager. Instead of so doing the lady took the necklet to another jeweler, who had previously valued the necklet for insurance purposes. As would be expected the value now placed upon the necklet was considerably less than before, whereupon the indignant lady took the pearls to the local police station and lodged a complaint against the first jeweler.
The police interviewed the jeweler and suggested that a laboratory investigation should be made. The necklet, now in pieces, for the police had cut from the necklet all the blackened pearls, came into the hands of the writer for an investigation as to the cause of the blackening of the pearls. From previous experiments it was known that some pearls appear to darken by possible sulphiding of a metallic compound, which may have adventitiously been taken up by the organic part of the pearl, or by dirty grease entering the pearl through the stringing canal. There is a further, but unlikely, contingency that silver nitrate, which is used in some hair dyes, might be the activating factor, just as it is used for dyeing pearls black.
Examination of the string of the necklet under investigation showed some grease to be present, and that the snap itself was covered by grease, and to such an extent that one of the diamonds set in it was completely covered and could not be seen. Grease was evidently the answer here, but for completeness of the investigation a test for sulphiding was carried out. This gave a negative result.
Some of the discolored pearls were then degreased by using a Soxhlet extraction apparatus. After this treatment the pearls were found to be much whiter, and grease was recovered from the solvent used for the degreasing.
What happened here was that grease, presumably from cosmetic creams, had entered, by capillary attraction, along the stringing canal and up and around the discontinuation layer between the bead nucleus and the outer nacreous layer. The grease had darkened, owning to ageing and admixture with dirt, and this showed through the translucent pearly outside layer and make the pearls appear dark colored.
(continued)
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