The hard and layered internal shell of Sepia officinalis, simply known as cuttlebone, is commonly used as food for small pets such as birds and reptiles. Yet, one of the most fascinating uses for cuttlebone was linked with fashion, since the internal shell of squids was traditionally employed for jewellery making.
Composed of a chalk-like material known as aragonite (calcium carbonate), cuttlebone has a microscopic structure consisting of narrow layers connected by numerous upright pillars. Its composition and structure allows it to be easily carved and withstand high temperatures at the same time, that's why it is ideal for metal castings.
As highlighted in this display from the Museum of Malacology in Cupra Marittima, this system - mainly used in the jewellery industry until the mid-'50s - is still employed by jewellery masters in Valenza, Italy, especially for one-piece jewels and men's rings.
The cuttlebone is usually prepared by cutting it in half with a saw (the length and thickness of the bone establish the size of the casting) and rubbing the two sides together until they fit flush against one another (sanding them can be useful to make sure the surfaces become flat).
A design is then carved into the cuttlebone with a blade and a funnel-shaped sprue with a channel is added together with air vents. Melted metal is poured into the mould via the sprue; the mould burns when the melted metal is poured in, producing carbon that keeps the metal clean from oxides.
When the process is finished the mould is open and the casting is removed with tweezers and left in a water bath. The sprue is then sawed off and the finished piece is polished. In the very final stage gems or precious stones can be added (though in this case, before pouring the melted metal, small wood cylinders will have to be inserted where the gems are supposed to be mounted).
As stated above, this technique is still employed by some artisans and it would be intriguing to see if younger generations of jewellery designers would be interested in coming up with small collections made with this system. Anybody up for the cuttlebone casting challenge?