Giovanna,
You poured pure copper, didn't you? Pure Cu has a strong
tendency to absorb oxygene when molten, that gather as bubbles
when it solidifies. This, combined with a possible slight
emission of carbondioxide from the limestone mould, may be the
cause of your bubble/porosity problem.
Anders
>----Ursprungligt meddelande----
>Från: [log in to unmask]
>Datum: 08-07-2012 08:32
>Till: <[log in to unmask]>
>Ärende: Re: Stone mould
>
>The depth of the moulds were about twice the thickness of a
regular flat axe. We thought that it might provide a reducing
atmosphere, so that the upper surface would not oxidise as
much. When we tried it out, it worked well and the upper
surface was much smoother than if the bronze had been poured
right to the surface. However, we did have a constant problem
with air bubbles forming on the lower surface (a photo of an
example is in O'Kelly and Shell 1978 in "The Origins of
Metallurgy in Atlantic Europe" p. 139).
>
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