Peter
I agree thoroughly with what Thilo has said.
However, I think its worth adding that red iron oxide/ochre is not a particularly common
material (in sufficient grade to be used as a pigment) within sedimentary rocks. The iron
oxide layers in your sandy sediments will typically be brown or yellow hydrated oxides. The
transformation to red in such circumstances is most likely through heat - either accidentally,
or as roasting ore for smelting, or for use as a pigment.
Even without a marked colour change, the application of heat to those oxides typically results
in enormous changes to their magnetic susceptibility - and use of an MS meter can detect
heated iron oxides (e.g. partly roasted bog iron ores) very easily.
If you have pigment production from sand-hosted pan deposits then I would expect to see
probably both heating and washing involved in the pigment production - and these should
leave recognisable archaeological traces.
In Britain the use of red iron oxide pigments was quite strongly associated with hematite
deposits hosted in the Carboniferous limestones - with uses from painting railway wagons, to
marking sheep (that pigment was known as ruddle) to Palaeolithic burial rites. Natural ochres
from the Forest of Dean are still worked for cosmetics - and there is an amazing natural
range from yellow to brown to red, even to purple.
As Thilo said, the difference between an appropriate rock and pigment is only its use.
Tim
On 16 Nov 2011 at 19:03, Peter wrote:
>
> Dear Thilo,
>
> Thank you very much for your response. I was afraid of this. It is indeed a problem of the use of
> natural pigments without extensive refinement.
> Also science has its limits.
>
> Thank you again.
>
> Best regards,
>
> Peter
>
> ----- Original Message -----
> From: Rehren, Thilo
> To: [log in to unmask]
> Sent: Saturday, November 12, 2011 4:51 AM
> Subject: Re: Ochre
>
> I'd say that there is no way 'scientifically' to identify natural iron hydroxides as 'pigment' or
> part of the local geology. Whether it is part of a rock (ie a mechanical mixture of minerals),
> or a mineral (as in a well-defined material of a specific structure and composition) depends
> on your sample size. Whether it is 'geology', or a 'pigment' or an 'ore' depends on the
> socio-economic context, ie its intended use. The latter you can't determine scientifically, but
> only by (archaeological) context and deduction / interpretation. A major deposit
> ofironhydroxide (say, a bog ore layer or iron nodules in a sandy matrix) could have been
> just a mountain for early humans, then being used as a mine for pigment in the Stone Age,
> and the same deposit as a mine for iron ore during the Roman or Medieval period, and now
> just be a mineral occurrence or anuisancefor the local farmers (since it is no longer
> economically viable to mine and smelt it in a modern economic context). Analytically, the
> material has undergone no change at all; what has changed is the way we humans see it.
> From own experience, it can be difficult in the field to distinguish whether something is a piece of
> the local geology, or an 'artefact' brought to (or used at) the site with a purpose. Material
> identification is only one aspect of this; knowledge of the local geology, careful context recording
> and sensible interpretation are other key elements.
>
> Having said this, there are a number of papers that look at how to determine 'intentionality' of
> use, scientifically. One way of doing this is by looking at indicators for heat treatment of iron
> hydroxides that may have been (intended to be) used as pigment: examples include Chalmin et
> al. 2004,Palaeolithic painting matter:natural or heat-treated pigment?, Applied Physics A 79,
> 187-191 (DOI: 10.1007/s00339-004-2542-0), or Manasse and Mellini 2006,Iron (hydr)oxide
> nanocrystals in raw and burnt sienna pigments, European Journal of Mineralogy 18, 845-853.
>
> And then there is the famous 'Kiruna red', a pigment used all over (northern) Sweden and named
> after the Kiruna iron ore deposit; or the processing remains from the pyrite / sulfur mines in Rio
> Tinto (Spain; note the name of that river...) used as a pigment; or the 'terra rossa' / bauxite soil
> that formed in specific (lateritic) conditions and can be just a soil, or a raw material for pottery
> (particularly for red-firing slips or surface coats), or an ore for aluminium production...
>
> Thilo
> UCL Qatar
> [log in to unmask]
>
>
> From: Arch-Metals Group [[log in to unmask]] on behalf of Peter King
> [[log in to unmask]]
> Sent: 12 November 2011 01:06
> To: [log in to unmask]
> Subject: Re: Ochre
>
>
> I have a faint recollection from the accounts of Ashburnham ironworks in Sussex, England, of
> the sale of something (possibly ochre) from what had been mined as iron ore to be smelted in
> the blast furnace. This suggests to me that they were selecting some of the best material that
> could be sold at a higher price. There is nothing in this in the compilation I made over a decade
> ago from my original notes, and the original notes would take me some time to locate.
> However, I have a suspicion that the commodity was not specifically "ochre" but something else
> - possibly rouge.
>
> Peter King
> 49, Stourbridge Road,
> Hagley
> Stourbridge
> West Midlands
> DY9 0QS
> [log in to unmask]
>
>
> From: Arch-Metals Group [mailto:[log in to unmask]] On Behalf Of Peter
> Sent: 04 November 2011 21:21
> To: [log in to unmask]
> Subject: Ochre
>
>
>
> Dear all,
>
>
>
> A Dutch archaeologist asked me if there are ways to make a clear distinction between ochre
> (used as pigment) and naturally ocurring ironoxide (as is foundin abundance in sandy deposits in
> the eastern part of the Netherlands). He found some redish material during an excavation near
> Eindhoven.
>
> Any suggestions ???
>
>
>
> Best regards,
>
>
>
> Peter Seinen
>
>
>
>
>
>
>
--
Dr Tim Young MA PhD FSA FGS
Email: [log in to unmask]
Web: www.geoarch.co.uk
Phone: 029 20881431
Mobile: 07802 413704
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