Paua shell

The nacre, or smooth inner layer of mollusk shells, is sometimes brightly colored and attractive. Some invertebrate animals have been hunted to nearextinction for their brilliant nacre. An example of this is the Paua shell,... 

The shell is partitioned into connecting chambers, with the mollusc occupying only the last one. The rest are filled with gas to give buoyancy. The inner layer of the shell is nacreous, and, as with paua shells, the periostracum can be polished away to reveal the nacreous layer beneath (Fig. 10.9). The material is most commonly used as mother-of-pearl inlay. 

Shells can be dyed, though this is usual only with abalotie or paua shells where a dye enhances or emphasises the colour already there, or with tiny, thin shells sold as ine ensive jewefiety (Figs 10.15 and 10.16). 

Dyed shell may have an artificially bright colour. Viewed with a lOx lens the dye can be seen to accumulate in patches. This is especially noticeable in the areas of organic matrix on the surface of dyed abalone or paua shell (Fig. 10.15). 

The shell industry is still very active in various parts of the globe, especially in the Far East, where every souvenir shop is stocked with items made of, or using, shell. In New Zealand paua shell is made into anything from beads to boxes, and mother-of-pearl and paua is made into laminates for wall coverings. Cameos are not only made in Italy, but also in Japan. Most of them are now mass produced, albeit by hand, for the tourist trade. In northern Europe it has long been a custom in every seaside resort to sell trinkets covered with shells, and shell necklaces are sold to tourists worldwide. 

Brown, Grahame (1986). Gemmology of the Cameo Shell. Australian Gemmologist. Brown, Grahame (1988). Paua Shell. Australian Gemmologist. 

Figure 14.6. A polished abalone (paua) shell from New Zealand (left) and a crystal of the mineral calcite (right). Both materials are constmcted from calcium carbonate, but in the abalone shell, the material takes the form of many layers, each a few hundred nanometers thick. These otherwise clear layers diffract light to impart the vivid colors seen in the shell.

The molluscs from New Zealand are known as paua, while their cousins across the Pacific on the American coastline are known as abalone. Both occur in glorious iridescent greens, blues, pinks and purples. The nacreous layer has a surface pattern resembling waves, which is caused by concentiatioiis of organic matrix. In the centre is a more uneven area where the animal was attached to the shell. The... 

Similarly thin pieces of shell such as paua and abalone may also be backed with plastic, filming a triplet. 

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