Hi Greg,
It seems that I have seen that horseshoes and nails were used directly in crucibles, but I did not think of it, the reason must be that it was not horseshoes, but mule shoes

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Persian Steel by James Allan and Brian Gilmour, pages 41-79. On page 61 a recipe is given where some of the things, which should be used, are mule shoes and nails. Other old recipes on how to make crucibles are also given.