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In page Cupellation:

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Archaeological investigations as well as archaeometallurgical analysis and written texts from the Renaissance have demonstrated the existence of different materials for their manufacture; they could be made also with mixtures of bones and wood ashes, of poor quality, or moulded with a mixture of this kind in the bottom with an upper layer of bone ashes.[2][3][4] Different recipes depend on the expertise of the assayer or on the special purpose for which it was made (assays for minting, jewelry, testing purity of recycled material or coins). Archaeological evidence shows that at the beginnings of small scale cupellation, potsherds or clay cupels were used.[5][6][7]