Corals are masterpieces of a coelacanth called polyps in the sea, and pearls and amber are organic gemstones, often growing in the form of dendritic branches. In different seas and depths, due to the different content of mineral elements absorbed during its growth process, it will grow into different colors, including white, red, blue, black, gold and so on. And those volcanic earthquakes in the sea, is the breeding ground of gem-quality corals, because the frequent activity of submarine volcanoes, for their growth provides a wealth of mineral elements, if they absorb a large number of iron-based substances, coupled with coral insects from plankton obtained by cartevin (a carotenoid), over time, it will gradually become the red coral we see.
The formation of coral is very long, so there is also a saying of "thousand years of coral red", high-quality red coral is warm and beautiful, and the handicrafts carved by it have often been given full of auspicious meanings since ancient times. For a long time in the past, due to overfishing, resource exploitation, environmental pollution and other factors, coral resources have been seriously damaged, and have been listed in the appendix of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) as a protected animal at the national level.
Figure 1 Red coral (photo source network)
Red coral
The surface layer of red coral is calcareous and has a glassy to waxy luster. Generally, the coral jewelry you have just purchased is red and bright, but some of them will find that after wearing it for a period of time, your luster becomes dull and its color is even white. The author received such a sample some time ago (Figure 2), the color of the red coral ornament has turned white, is the coral quality not good or there is another mystery? So what is the white substance on the surface of the red coral bead chain? Let's explore it together.
Figure 2 Sample photo(1)
Figure 2 Sample photo(2)
Microscopic observation
Observed under a microscope at 10-40 × (times), it was found that these white substances were different from the form of the white core in the red coral, which was part of the coral body, the same chemical composition as the red part, the luster was consistent, the glass luster was to waxy luster, and it was white only due to the absence of carotenoids (Figure 3).
Figure 3 Red coral white core
The white powdered substance in front of me is matte and adheres to the texture, pits and crevices on the surface of the coral, and is more common in the wearing position of the bead chain and less near the bead hole (Figure 4).
Figure 4 Photo under a and b-10x magnification conditions, c and d-40x magnification
Infrared spectrometer testing
A small amount of white material was scraped and tested by attenuated total reflection (ATR) using Nicolet IS10 infrared spectrometer, with a resolution of 8 cm-1, 16 scans, and a test range of 400 to 4000 cm-1. The infrared test results show that its line is similar to the reference map of lactate, that is, the main component of the white part of the sample is lactate (see Figure 5).
Figure 5 Red is the sample ART infrared spectra, and purple is the lactate infrared spectrogram
The main component of coral is calcium carbonate, which is unstable in nature. The chemical components in skin care products, including human sweat, contain lactic acid, fatty acids, etc. may have a chemical reaction with it, so it is inferred that the white powder crystal that appears in the close position of each bead is a white crystal formed by the chemical reaction between coral jewelry and human sweat or skin care products. The deterioration of luster is due to the low hardness of corals, and quartz particles in the air may cause wear and tear on it, so the corals that have just been polished are glass luster, but after long-term wear, they may become waxy and shiny under the influence of daily environment. If this is the case, repolishing is an alternative.
Tips:
Coral-like organic gemstones include pearls, amber, etc., and their chemical stability and hardness are relatively low, so you should understand the special conservation methods of these varieties before purchasing. For these natural gems, careful care can keep them radiant.
Coral products should not only be well maintained, but also well protected when worn.
1. Avoid contact with acids and nail polish, detergents, perfumes, lotions, etc.
2, avoid exposure, prevent continuous constant temperature baking, coral will lose color and luster due to exposure and high temperature.
3. When wearing corals, they should avoid rubbing with hard objects, especially metals, and avoid rubbing with other inorganic gemstones and jade.
4. Coral jewelry storage should be placed separately in the jewelry box to avoid rubbing with other jewelry.
5, coral necklace is best to re-string every few years. Knots are knotted between each bead when threading to prevent friction between the beads and to prevent the beads from falling apart in case the line breaks.