No.96 in the 'Catalogue of Curiosities' is described as 'A rasp made of a ray's skin.' It is in the section of objects from the Friendly Isles (Tonga) but files made from shark or ray skin were commonly used throughout the Pacific for smoothing wood, or for grating sandalwood to perfume coconut oil.
In use, the piece of skin was usually attached to a piece of wood using coconut fibre cord, although Charles Hedley, a naturalist who visited the Ellice Islands in 1896, suggests that 'an unmounted fragment, such as a piece of the tail (of a ray) sometimes served.' *
The skin of sharks and rays is covered in placoid scales, or dermal denticles. These are very similar to mammalian teeth, the outer layer being covered with a hard enamel-like substance. These scales give shark skin its hard rough texture, ideal for smoothing wood.
|The skin surface (x6) showing the dermal denticles|
According to Reinhold Forster in 'Observations Made During a Voyage Round the World',when considering the inhabitants of Tahiti, 'If we consider that a stone adze, a chissel of the same materials, or of bone, and a piece of rough coral rock, together with a saw made from part of a sting-ray’s skin fastened round a piece of wood, are all the instruments to assist them in the structure of their houses and boats, we must certainly give ample testimony to their ingenuity.’**
* The atoll of Funafuti, Ellice group: its zoology, botany, ethnology, and general structure based on collections made by Mr. Charles Hedley, of the Australian museum, Sydney, N.S.W. 1897. Sydney. Part IV - 'The Ethnology of Funafuti'
** See previous post for reference