Peter,

thanks for that very thorough reply.

Coming from this problem at the other end of "how to make one", I'm faced 
with three very obvious problems:-

1. What mould (or is it mold) material to use.
2. What shape to use.
3. What post-mould work to do on the blade.

Regarding the material So far I have tried sand and clay as the "obvious" 
materials. Surprisingly they worked remarkably well which led me onto the 
next problem.

The shape (and related - the precision and detail of the mould).

After a bit of effort I have the shape and size of a number of axe blades 
"as found". But what I don't have is a size and shape of the mould used to 
produce these blades as the blade is likely to have been worked after 
moulding. Which then begs the question:-

What post mould work was carried out on the blades?

My experience with a copper blade is that it is not too difficult to 
substantially change the shape after moulding, but any working makes the 
blade thinner. Therefore the mould shape must be thickened where it is 
intended to work the blade.

Peter, you say the whole blade has been worked. Do you have details of the % 
thinning and how did it vary in different places on the blade?

Finally, what was the final heat treatment? Is it cold working after 
quenching? Is it cold working after allowing to cool? Is it heating and then 
allowed to cool after final cold working?

Mike


----- Original Message ----- 
From: "Peter Northover" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, October 11, 2007 1:27 PM
Subject: Re: [ARCH-METALS] Flat bronze axes - tooling marks or restoration?


> Dear Mike,
>
> The first quick answer to your questions is that some axes were cast in 
> one-piece moulds and some, usually copper axes (in Britain before about 
> 2150BC) do show clear evidence of this. The evidence might be a rough 
> surface or, if you take a core right through (which we have done on a 
> couple of unprovenanced axes, there is a clear density gradient of oxide 
> inclusions showing how oxygen has been absorbed from the atmosphere into 
> the solidifying metal. One should be careful, though, in saying open 
> mould. Experiments we did many years ago showed that putting a flat stone 
> or slate as a lid on the mould cut down the surface roughness greatly and 
> the meniscus at the cutting-edge and butt ends went part of the way to 
> shaping the blade. The ideal is to have the molten metal just in contact 
> with the lid and not poured so as to lift it. Also, if the metal was 
> poured gently in this way there would be a meniscus along the edges as 
> well and no flash. In Middle and Late Bronze Age axes which were 
> manifestly cast in by valve moulds the position of the flash line may 
> often be assymmetircal. This could be for a practical reason, for example 
> so the matrix for an attachment loop need be formed in one valve only.
>
> Having done metallography on probably 100 or so flat axes it is very 
> evdient that in the majority of cases, especially the bronze ones, that 
> the whole blade has been hammered and annealed and possibly planished as 
> well. Thus the surface of most of the axe has been smoothed by hammering. 
> Whether they were also ground and, sometimes, even polished is something 
> that has to be judged on a case by case basis. Of course, the faces and 
> sides of the axe might then be decorated, or in the case of one class of 
> Scottish flat axes, tinned.
>
> The symmetry of many of the axes, both bronze and some of the later copper 
> ones, does suggest the use of a bivalve mould. The alternative would be a 
> lot of hammering and I am sure this was done too. Don't forget that metal 
> technology came late to Britain and that the necessary technologies were 
> well established on the continent, where more complex shapes had been cast 
> for some considerable time.
>
> The place I would expect to see the most visible grinding marks (with a 
> stone rather than a metal file the latter beign a tool they did not have 
> in our Bronze Age) is on the cutting-edges of the axes, especially when 
> they were being re-ground by the user.
>
> The real key to undertsanding the way these axes wre made is definitely 
> under the surface in the macro- and microstructure. The right samples can 
> give you a quantitative measure of how much the axe has been alred in 
> shape, and where, what the annealing temperatures were, possibly waht the 
> casting conditions were, etc. Find an unprovenanced axe and take it to 
> pieces. You will learn an awful lot, and it will give you many more points 
> of comaprison for experimentally produced axes.
>
>
> Yours,
> Peter
>
>
>
> -- 
> Dr Peter Northover,
> Materials Science-Based Archaeology Group,
> Department of Materials, University of Oxford
> Tel +44 (0)1865 283721; Fax +44 (0)1865 841943 Mobile +44 (0)7785 501745
> e-mail [log in to unmask]