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High temperature silver solder: eutectic solder


#1

Please, I need some help/advise:

I went through the archives and found a lot of on IT and
eutectic silver solders. The specific use is to solder a fine silver
cage for Plique-a-Jour enameling.

I just made some eutectic solder for enameling (72% fine silver and
28% pure copper). I was very careful to clean the fine silver and
copper before weighing on a digital scale.

I then melted it together on a charcoal block with an acetylene
torch using a flux made of half borax and half boric acid. I melted
and stirred with a

Wood dowel, let it solidify and then melted and stirred again twice.
I let it cool a bit and then into pickle made of sparex.

The problem: the top surface of the ingot (10 grams total) was
copper colored! The bottom was a nice silver color. The copper looked
like a plating

That you can get with contaminated pickle (by iron). The copper
coating could be brushed off by hand with a brass brush.

I used a coarse file to create filings and soldered a piece (using
Battern’s flux) that survived 1435 in the oven for 120 seconds. The
piece was a 5 mm long rectangle 2 mm wide soldered at a 45 degree
angle by an acetylene torch and then placed in a dental porcelain
oven.

So the solder works just fine but the copper coating only on the air
surface is a mystery!

Does anyone have an explanation?

Thanks
Charles Friedman DDS
Ventura by the Sea


#2

The copper that oxidized during your melt floated on the top of the
melt as it is less dense than the metal, the silver oxides formed by
heating are not stable and returned to silver metal during cooling.
The pickle managed to reduce some of the copper oxide back to
metallic form. That is my guess.

Jim

James Binnion
James Binnion Metal Arts


#3

Charles,

I cannot explain this, but I would not worry about it. I also make
eutectic solder (I use 70% Ag and 30% Cu)and my ingots are
discoloured also. I made shibuishiusing 15 % Ag, 30 % and 50% and
theseingots were discoloured also. The plating can be easily removed
by putting the piece in a 10 % sulphuric pickle for a couple of
minutes or use sodium bisulphate with a drop of hydrogen peroxide. I
like sulphuric acid because it pickles very well, but I read on an EU
data sheet that exposure to sulphuric acid fumes is carcinogenic. I
am using a German pickle now.

As for the plique a jour, I am not sure at all that the solder will
hold up. I would not do plique a jour on a silver soldered piece.

Best, Leach


#4

The molten pool is exposed to atmospheric oxygen at the top. The
bottom is shielded. The copper will oxidise, then the oxides are
somehow reverted to copper. This will happen when the ingot is
quenched in alcohol, but can also happen in other mysterious ways.


#5
The copper will oxidise, then the oxides are somehow reverted to
copper. 

Alloying copper with gold or silver is not trivial. Copper oxidizes
very easily and could form metalloid compounds, which would render
alloy unusable.

The practical method for a craftsman is to roll copper very thin,
glaze it with borax, and introduce into gold little by little, after
gold is completely melted. Good cover flux is a must.

Leonid Surpin
www.studioarete.com


#6
The molten pool is exposed to atmospheric oxygen at the top. The
bottom is shielded. The copper will oxidise, then the oxides are
somehow reverted to copper. 

I suspect that the red layer is not metallic copper but is cuprous
oxide, which is also red. It will be removed by bright-dipping
(PhDown + hydrogen peroxide; or, dilute nitric acid, if you have some
on hand).

Judy Bjorkman


#7
I suspect that the red layer is not metallic copper but is cuprous
oxide, which is also red. It will be removed by bright-dipping
(PhDown + hydrogen peroxide; or, dilute nitric acid, if you have
some on hand). 

No, I have seen this before it is definitely metallic copper not
cuprous oxide.

James Binnion
James Binnion Metal Arts