Copper Casting In America (Trevelyan)

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Possibly, probably. But more importantly, there is still an volume of gas bubbles trapped inside the ingot, that is equivalent to the volume of the blob sticking out of the upper left hand side.

Yes

They are a result of the small air bubbles trapped throughout the metal caused by melting it in less than controlled conditions. Pure copper, direct from the mill, melted in a vacuum furnace, or a void and inclusion free piece of native copper, would forge out as well as the upper alloyed sample.

not also depend on the

I have added a 4th picture to the above mentioned url to address this. It is of a forging made from manufactured bar. In fact it is made from the same bar that made up most of the cast piece.

The cast piece was annealed 8 to 10 times in the course of it's forging. That is a lot, considering it's length was only increased by 50%. But the large crack on right the appeared in the first round of hammering and I didn't want the piece to fall apart.

The piece made from manufactured copper was annealed twice. I probably could have done the forging with out annealing at all, but it was a small piece being held in my fingers. As the hammering hardens the metal, more vibrations travel up the metal and into the hand. It can be quite painful.

For the sake of orientation, the sectioned surface of the ingot is the small end of the forging.

The outer surface of the casting solidifies very rapidly, and is usually bubble free, the bubbles tend to be trapped inside. Subsequent forging would mash these shut (although not bond them together) making them difficult to see in a radiograph as they would either be smaller than the resolution or look like regular forging flaws.

This is why radiographs are inconclusive an any piece that may have been forged.

This is true, but as cast copper is as soft as it can be and needs a significant amount of hammering to harden it. For any edged tools or fish hooks or awls, this would surely display the tendency to fracture. Sheet goods also would require a lot of hammering. Heavier decorative items or ceremonial pieces would require much less work and cast preforms would work fine.

Yes, that appears to be the rub. And is an area in which someone should undertake some real hands on research.

Otherwise, it is like the old saw about the man who lost his keys late one dark night. He spent the rest of the night looking for them beneath the only street light that he passed, because if he lost them anywhere else, he wouldn't be able to find them in the dark.

Paul K. Dickman

Actually, Mokume Gane is not a brazing process, but a diffusion bonding process similar to forge welding.

It occured well below the melting point of all the alloys involved.

I cannot speak to the state of the science now, but back in the late 70's, when I was doing research on it in college, our theory was this.

At elevated temperatures the grain structure of the metal undergoes enormous changes (this is what causes annealing) as the grains grow they can grow between separate but closely associated pieces of metal, Assuming that the junction is chemically clean and free from oxides.

Actually it can. metals alloyed together have an Gestalt proportion called the eutectic. In the case of silver and copper it melts at a lower temperature then either.

But the term sweats as it applys to Mokume gane is kind of a misnomer. It comes from the amount of blacksmiths we had on the project. It was a term they used in forge welding iron, and refered to the surface geting a greasy or oily appearance as the welding temperature is acheived.

For Mokume, the rule of thumb that we used was that this temperature was roughly 2/3 of the eutectic temperature of the alloys involved.

Paul K. Dickman

Eric,

My understanding is that 'native copper' is a term meaning 'pure copper' (well over 99% pure as found), and not a reference either to copper 'native' to, say, the Keewenaw Peninsula of the Upper Peninsula of Michigan, or to copper used by 'native' peoples. By that definition, copper that needs smelting is not 'native' copper.

Sort of like 'meteoric', init?

Tom McDonald

Eric,

I thought I recalled that they may have been given, perhaps by the Smithsonian, to a much smaller museum. Kelley Museum? Something like that.

Or I could be conflating two stories.

Tom McDonald

My recollection is that they were given to a repository for archives.

Eric Stevens

The point is we are discussing the possibility that some native copper may have been s/melted. Putting a fence around the definition of 'native copper' means that we have to find another word for copper s/melted by the natives. That all native copper is pure is merely an assumption.

Although some object to it. 'meteoric' is a precise description of the type of copper used by North American natives to make many (if not all) of their known artifacts. There is no absolute reason why the natives should not have used other sources of copper.

Eric Stevens

Actually I referred to neither. I referred to the use of pressure only as "merely by pressure" was your point.

Eric,

No, it is not merely an assumption; it is a definition. There was copper ore that was not pure. It would be called 'copper ore', or other names (halfbreed, etc.) specific to the type of ore body present. I think it useful to use the terms by which the metal and its compounds are known in the area we are discussing.

I don't think it is useful to use the construct s/melted. Melting can occur without smelting, in native or drift copper that is already pure. Smelting is necessary early step in a process to extract copper from ore. Melting may or may not happen later in the process.

Perhaps I'm over-sensitive about s/melt just now. Seppo has been playing silly buggers with that term, and it raises my hackles a bit. Still, I think it useful to use the terms separately.

Tom McDonald

I don't actually SEE any bubbles at all in the pigs, not even when magnified to its largest extent - where 1 cm = 3.5 cm on screen.

Now in this item I can definitely see "holes" that you call "porosity"

- and you have difficulty accepting it as cast - despite it clearly displaying the shape a mould. I would even suggest that this metal was well overheated when it was cast from the pure look of it.

The items are pre-Columbian from around 1300 AD. They are described as "Two copper pigs". I accept their view of it being copper.

It is malleable in relation to granite but then so is steel....

Fahrenheit is a long ago discarded temperature measure here and it is fairly meaningless to me - however the 500F appears to be a temperature people use to bake cakes or roast a leg of lamb in a standard domestic oven. I don't even see the copper glowing red from heat at that point. Naturally annealing can be done at almost any temperature, but from other things I have read, much much higher temperatures are in fact used before the term "annealing" is applied to it. Eg go get the metal red hot.

But one thing that does puzzle me in this claim of yours. A piece of pure copper, as a result of bringing it up to baking temperature can cause "bubbles" - forget the baking, take it to dark red state to form "bubbles". From what does the "bubble" form, we are talking about pure copper here? How did (whatever) get INTO the copper to form a bubble in the first place?

Totally irrelevant. But you do point to an external source for the bubbles by that example - so how does it actually get INTO the copper in the first place if it isn't (partially) melted?

No it can't. "Pressure" in itself does almost nothing. A loaded freight train running over a "copper" coin only flattens it and does nothing else. It is the sudden impact pressure that causes the molecules to move rapidly, that causes FRICTION, which in turn causes heat and if sufficient sudden pressure is applied (eg hammer blow to already hot metal) it CAN melt the material. To "weld" something by definition requires bringing part of it to a liquid state - ie melted in the portion being welded.

WELD - verb [with obj.], join together (metal pieces or parts) by heating the surfaces to the point of melting with a blowpipe, electric arc, or other means, and uniting them by pressing, hammering, etc - OED.

Though I note that "metals" isn't the only things welded - plastic is also welded, but the rest applies just the same. It also reminds me of an axle being welded onto the wheel mounting flange. The axle is placed against the flange with pressure, and spun very fast. When suitably hot, the rotation was stopped, added pressure was applied, the axle was pushed in on the flange by about 1 cm, this to weld it. This melted the material in the joint part as well as expanded the contact area.

The evidence exists that casting was used - Eric Stevens has provided expert testament to that effect. I have pointed to actual evidence (such as exists) including in this post. You label cast copper as "of no use to anyone" when it obviously was of use. You are probably very right in everything you say -for today's use when high quality melted copper can he had - but that isn't the issue at all. Frankly, if you find it "useless" in your endeavours is irrelevant, it doesn't mean the ancients did. YOU are not them.

You are very quick at labelling "wrong" without a single shred of proof or alternate theory! I therefor totally reject such unsubstantiated claims as worthless.

It is indeed that.

[..]

Well...... he did as God to get out of his chair.... if that is any indication...

You say it started off as a steel disc. You have not mentioned two pieces which were welded together.

describes the manufacture of gears using a similar process to that used for the Mini.

Eric Stevens

---- snip ----

You are wrong, particularly in the case of copper. The power in your house comes to through a large number of cold welds formed merely by pressure. This is true irrespective of whether you are supplied via copper or aluminium cables.

How do you explain the well known welding at ambient temperatures of precision slip-gauges made of hardened steel? Leave them in contact overnight and you will be lucky to get them apart in the morning.

--- snip ---

Eric Stevens

Please point me to a source.

Eric Stevens

Well, that's what happens when a term is abused.

In any event nothing prevents the pure copper from also being melted - specially not a badly though up term. The point being making small pieces into big pieces.

No. While true cold welding can occur, that's not the mechanism(s) responsible for wringing gage blocks together.

Frankly, the exact details are still in dispute. Part of it is atmospheric pressure differential between the outside and the area where air has been forced out from between the blocks. (up to 14 PSI) Part of it is often due to the stickiness of oil on the blocks. (roughly 2 or 3 PSI)

But neither mechanism is strong enough to account for the amount of force typically needed to separate the blocks. (typically on the order of

100 PSI)

Most experts believe that Van der Waals forces (the same forces that give water surface tension, or make solder adhere) are responsible for the bulk of the effect. Others now point to the Casmir force (a quantum effect). Lively disputes still continue.

A true weld is as strong as the parent materials. (up to 200,000 PSI for tool steel gage blocks) When you break a true weld, parts of the parent materials are ripped out. That doesn't happen when separating wrung gage blocks. So that's not an example of actual welding.

To do an actual weld, the atoms of one piece of material have to be brought as close to the atoms of the other piece of material as the atoms of one of the pieces are to each other. At room temperature this requires a lot of force, on the order of the yield strength of the material.

This is a few thousand PSI for relatively low yield materials like copper, or more than 100,000 PSI for materials like tool steel. Of course, as you increase the temperature, the yield strength of the material declines, and less force is needed. When a material melts, the yield strength goes to virtually zero, so little or no force is required to achieve a weld.

Gary

... when he quoted my response to it.

You are discussing the underlying welding mechanism. The point is that, in those circumstances, welding occurs without either heat or significant pressure, irrespective of whether it is due to Van der Waals forces, the Casimer force, atmospheric pressure or whatever. I do know that if such gauges are left in contact for sufficiently long it is virtually impossible to separate them.

That is very rarely the case.

It depends upon how long you leave them together.

So?

But we (Seppo and I) were discussing welds at ambient temperature. See

Eric Stevens

Yeah well..... that isn't really what happened despite there being several substances in that same solution - as they would all have ended up in one glorious mix.

Never had anything fly off an aircraft that wasn't intentionally thrown out of it..... or a mob of disgruntled passengers who decide to get off in mid air at some 4000 ft as it is the fastest way to the pub....

Actually that is a page I had found... but lost again, as I wanted to use an image from there to demonstrate the NEED to melt even pure copper:

A good site!!

By definition "welding" does refer to melting of material to be joined

- be it in a forge, oxyacetylene or mig welding or whatever.

Actually no "alloys" are involved - they are pure materials laminated in mokume gane.

I'm pretty sure that will be close enough still :-)

Isn't this what "brazing" refers to?

I'm aware of that, but these are not alloys - these are pure metals made into a "Dagwood" sandwich - therefor the "eutectic" thingo doesn't apply. If on the other hand you speak about a real copper/silver alloy, as per your experiment - that is a different story.

Whoever it was that said this, it was a person familiar with making mokume gane. It is a visual indication of having reached the desired point "when the silver starts to sweat" not the copper, but silver, that has a lower melting point - a method that was used in ancient times before thermometers and fancy little bench top gas kilns were invented.

...which is only just below melting point - yes THAT look I recognise.

That would be fine IF you were using "alloys" - in my example no alloys are involved.