In article , Harold & Susan Vordos says...

OK, lets talk about this in a slightly different light. In industry,
there is a solder that is called "silver solder". It is a solder
comprised of silver and copper, generally with some sacrificial element,
often cadmium. It has a color similar to brass. The alloy varies, but
it runs in the area of 50% silver. It is not solder for silver. There's
a huge difference. Most people associated with the machine industry
understand what silver solder is.

(snip)

The terms 'silver soldering,' 'silver brazing,' and 'brazing'
are often used interchangeably in industry. "Braze welding"
or brass welding is quite different as a rule.'

(snip)

... Silver solder is not a filler material, and is most effective when
there is a proper fitting of the components.

Yep. The silver solders with cad in them will flow like crazy into
the tinyest crack or joint. There is really no need to leave a
gap for the filler the way that soft solder requires. My favorite
story was related to me by Arthur (Bud) Embry who was the 'torch
brazer' at work when I hired on there. I learned to silver solder
by watching this man. He said that during WW2 the liners were
pressed into anti-aircraft barrels and then a gang of men with
rosebuds would heat up the entire barrel to the flow temperature,
and then the silver solder would be applied to one end of the
barrel liner - and it would wick all the way down the five or
so feet and appear as a bright ring at the other end.

I'm not sure exactly what constitutes brazing as opposed to soldering, for
in each case the base metal is not melted, but the soldering medium is. I
get the idea that the main difference is that in brazing one can effectively
build up an area with the brazing material, whereas in soldering it is to
be discouraged, and works poorly when attempted. Where's Ernie when we
need him? g

Again, the term "braze welding" is typically used when one is building
up a joint like that - when the entire item is not brought up to the
flow temperature. But when the entire joint is brought to the
flow temperature this is brazing. The heat can be applied via
torch, or sometimes by placing the entire item in a furnace with
a controlled (typically reducing) atmosphere. In the latter case
one can use things one does not typically think of as a braze material,
for example, gold, copper, nichrome. These can be applied in advance
to the joint as a preform (ring or sheet) or can be applied as
a paste of binder and metalic powder. Extremely intricate work
can be done this way. Bud was in charge of the hydrogen furnaces
and after he died things kind of were never the same. A real
craftsman.

No doubt somebody will chime in here and claim I am full of it, (probably
am) but I think that if it melts above about 900F then that is brazing
and below that it is soft soldering. Purely an arbitrary line drawn
in the (temperature) sand because the process is *exactly* the same:
joining two similar or dis-similar materials, using a third material
as a kind of inter-atomic 'glue.' The adhesion forces that make
solder of any kind stick to another material's surface are not really
well understood by physicists in general. There is considerable
discussion even now about the physical processes of "adhesion" in
some industries. Like mine.

The qualities of lead you described are exactly why one should never uses
lead with precious metals. The solvent qualities are apparent even al low
temperatures. Platinum, for example, melts at over 3,000 degrees F, but
dissolves in molten lead. It is lead's solvent quality that makes it so
useful when assaying. It is introduced to the heat in the way of
litharge, along with the appropriate fluxes for the assay in question.
The lead that is reduced from the litharge dissolves traces of precious
metals and concentrates them in the lead so they can be recovered. The
lead is once again reduced to litharge in the cupelling process, leaving
behind a button comprised of the values.

I found out how well lead can dissolve gold the hard way - by trying
to solder a 0.003 inch diameter gold wire with lead-tin solder.
Talk about frustration!

But to re-cap: The following terms really mean the same thing:

Brazing
Torch brazing
Silver soldering
Silver brazing

When one lumps up brass on a cold item, that is
best called brass welding or braze welding.

Jim

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