"Paul K. Dickman" wrote:

In order to illustrate the nature of the porosity in melted copper I put a
few
pictures up.

http://tinyurl.com/3cw7p

Very interesting!

The first labeled Casting is a small ingot cast of ca110 copper It started
out
essentially 99.9% fine. The casting method was about as simple as you can
get.
It was melted with an oxy-acetylene torch and poured into an open mold, made
by
scraping a depression into some foundry sand.

The "cocks comb" sticking out in the upper left is not a sprue. When the
pour
was finished the ingot was shaped like a little loaf. As it solidified,
dissolved gasses came out of solution with the metal. As they did they were
trapped by the solidified metal on the outside of the ingot and built up
pressure. Eventually a weaker spot in the surface of the metal gave way and
metal and gas squirted out. Like stepping on a ketchup packet in the
McDonalds parking lot.

I can't say I can speak from experience on that issue :-)

The size of this is indicative of how much gas was dissolved in the metal.
It is approximately 10% of the original volume of the ingot.

Essentially what you are saying is that a lot of the gases escaped
before it solidified.

The rough area in the lower left is not indicative of porosity, It is where
the metal first struck the sand. When it did, it's surface tension was
sufficiently
disturbed to allow it to flow into the spaces between the sand grains.

The second picture, labeled section, shows what this looked in a cross
section cut at about the base of the "cocks comb"
You can easily see the large bubbles. It also has a large amount of small
bubbles that are visible under a 10 power loupe.
You can see that it looks very similar to the R666 radiograph. However that
piece looks more like a mistake than a deliberate casting.

....or just a casting to make small pieces into one big piece?

You can also see that it is not a single round bubble but a miriad of
amorphous blobs.

....still similar to R666....

The third picture, labeled forgings, shows it's workability.
The lower shot is from the pure copper ingot, You can see it is full of
fractures and tears.

I assume this is from the melted copper described above? Are you
suggesting the "tears" are the result of (A) the pure copper having
been melted (B) because it is pure copper? If (A) how does it compare
to not melted copper of equal grade? Would it not also depend on the
handling of the material if it tears or not - eg more frequent
annealing - hot working etc?

If it is from the melted ingot - what has happened to the "myriad of
amorphous blobs" - they are no longer visible.

The upper forging is made from an ingot cast from approx. 4% silver-96%
copper.
This ingot exhibited no cocks comb and the forging was made from the entire
ingot, with no waste removed.

The two metals are visually identical, but one casts like crap and the other
doesn't.

If something is acceptable or not, depends on the use and views of
acceptability on the day. If something was melted to get a single
lump, to be later beaten into a sheet for further working to jewellery
for instance, then perhaps it really doesn't matter - perhaps it may
no longer even be obvious to have been cast.

If they were casting on any scale, it is not just inevitable that alloying
occurs, it is pretty much a necessity.

I doubt there was any real high volume of casting occurring,
considering other sources. However the lack of scraps and off cuts
note, as well as the storing of off cuts in a bag with other copper
artefacts and a sheet of copper indicates scraps were used up.

If you want to prove casting, stop stroking around with radiographs and look
for alloying.

Well..... there is the problem. This information hasn't been gathered
of either kind to any extent to my knowledge. The radiography (or
analysis) of two items... or even a dozen items, is not representative
of the tens of thousands of artefacts found.

--
SIR - Philosopher unauthorised
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The one who is educated from the wrong books is not educated, he is
misled.
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