I have no trouble soldering sterling or fine silver but this bronze
(11% tin, 89% copper) has got me buffaloed. It is fired from the
BronzClay but it is true bronze. I bought bronze solder from Rio,
fluxed using my regular silver flux. But the bronze blackened
immediately (oxidized) and the solder would not flow. I thought
putting the piece on a charcoal block would help create the
reduction atmosphere that the bronze needs to keep from oxidizing,
but no go.
Anybody have any experience with this? Any suggestions?
I have soldered BronzClay pieces just a few times so far, using
ordinary silver solder. A couple of attempts have been failures–
the solder runs all over but not into the joint. So, a couple of
thoughts-- First, like silver clay, the bronzeis presumably porous,
even though it is very hard. So burnishing the area with a hammer
handpiece may help, as well as withdrawing the heat sooner, when the
solder just slumps. Also, I’m getting the sense that what flux you
use may be important. The Magic Flame I use in my own studio seemed
to work well; the borax and alcohol at the studio I teach in didn’t
seem to. I hope someone else knows more!
I suspect that your regular silver flux is breaking down before the
piece has reached temperature. We braze and weld a number of bronze
castings and I would note that a TIG torch using a silicon bronze
filler rod is a substantially more effective method of jointing. On
the limited occasions I employ a torch I will apply a very liberal
paste of a high duration flux, in our case Johnson Matthey Tenacity
No, 6.
I have absolutely no experience with soldering bronze metal clay but
I would try a black (boron modified) flux. It is available from Rio
and other vendors of brazing materials. It will have the best chance
of deoxidizing the surface enough to allow the solder to wet the
surface if it is a flux issue.
The composition of bronze must be effected immediately before
the casting, for bronze cannot be kept in store ready prepared.
In forming the alloy, the refractory compound, copper, is first
melted separately, the other metals, tin, zinc, etc., previously
heated, being then added; the whole is then stirred and the
casting carried out without loss of time. The process of forming
the alloy must be effected quickly, so that there may be no loss
of zinc, tin, or lead through oxidation, and also no
interruption to the flow of metal, as metal added after an
interval of time will not combine perfectly with the metal
already poured in. It is important, therefore, to ascertain the
specific weights of the metals, for the heavier metal will
naturally tend to sink to the bottom and the lighter to collect
at the top. Only in this way, and by vigorous stirring, can the
complete blending of the two metals be secured. In adding the
zinc, great care
must be taken that the latter sinks at once to the level of the
copper, otherwise a considerable portion will be volatilized
before reaching the copper. When the castings are made, they
must be cooled as quickly as possible, for the components of
bronze have a tendency to form separate alloys of various
composition, thus producing the so-called tin spots. This is
much more likely to occur with a slow than with a sudden cooling
of the mass.
I’ve had similar problems soldering bronze, brass, or stainless steel
when I used my normal flux which is formulated specially for precious
metals. When I used EasyFlo powder mixed to the usual creamy paste
consistency, the problems went away. If the items take a long time to
reach temperature then use a flux like Tenacity; but be aware that
it’s much more difficult to remove afterwards.
I’m not sure what the mystery is. I work in silicon bronze very
often. I’ve been making forged buckles lately. Bronze–I use the
alloy Everdur from Atlas metals–hot bends beautifully, forges and
welds.
I solder it with silver solders, brass brazing rod or, lately, just
plain sterling. Works great.
I use Dandix paste flux, but any good flux should work.
Visit my website–andycooperman.com-- for examples of bronze used as
fabricated elements.
I really don’t appreciate the moderator putting these words in my
mouth. This is not what I posted in reply to Delores. By what
stretch of the imagination did you(the moderator) think it was ok to
post this in my name? I expect a public statement saying you did
this.