Hi Lyle
I think that the change in color probably corresponds to a change in slag
composition, but this could be attributable to a change of flux (or the
proportions of flux to ore) as well as to a change of ore. In my
experience slags that are light blue or turquoise are fully glassy slags
that are mostly composed of oxides of calcium, magnesium, silicon and
aluminium - the calcium and magnesium deriving from heavy additions of
limestone or dolomite flux. I haven't had much experience with the green
or purple slags that you mention, but the green color might suggest a
higher proportion of iron oxides than in the blue slags.
Dave
On 7/22/13 10:06 AM, "Lyle E. Browning" <[log in to unmask]> wrote:
>Mossy Creek Iron Works was a charcoal fired, cold blast furnace in
>Augusta County, VA, USA that nominally operated from 1774 to 1841 when it
>burned. The typical glassy slag color is dark green, or an almost purple
>or some tint of dull blue. After the associated forge and foundry ceased
>operation in 1880, the property was sold to a grist milling company who
>erected a crib dam in 1903 that had a fair amount of robins egg blue to
>turquoise blue slag. There are also reports that other areas nearby have
>the same used as fill around culverts and so forth. The presumption is
>that the slag was from the ironworks and not imported from elsewhere as
>crib dam fill.
>
>Is there anything that would cause a color shift in the smelting process
>other than a change of ore source?
>
>Thanks in advance,
>
>Lyle Browning
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