On Sun, 04 Jul 2004 11:21:41 GMT, Seppo Renfors
wrote:



"Paul K. Dickman" wrote:

Seppo Renfors wrote in message ...



I already said it was brazing. I couldn't think of the specific
decoration name before, but it is used in making "mokume gane" as
found, and originating on samurai sword handles from about 1600 -
1800.

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

By definition "welding" does refer to melting of material to be joined
- be it in a forge, oxyacetylene or mig welding or whatever.

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

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

Hmm.

http://www.mokume-gane.com/Pages/What_is_Mokume.html

"The billets, composed of various combinations of gold, silver
and copper alloys ....

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.

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

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.

Isn't this what "brazing" refers to?

No.

Are you suggesting silver "sweats" (forms liquid beads) way below its
melting point?

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.

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.

A eutectic can a,d soes apply in some cases, at the interface. Copper
will do this with gold, silver, aluminium and zinc, and no doubt a few
other metals besides.

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.

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.

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.

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

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.

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




Eric Stevens