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Soldering bi-metal

Looking for advise on soldering bi-metal. I’m using 18K/sterling and
trying to solder an 18K bezel on the sterling side. It seems to take
a LONG time to get the easy silver solder to flow on larger pieces
(say 2" x2" area). I’m using acetylene with a goss torch.

Beverly Schnell

Beverly -

I’m guessing you are using the 20g sheet? From the sound of it, you
are not getting the metal hot enough. I don’t know what a goss torch
is…I use a Smith acetylene/air torch, and have no trouble with the
18k/925 bimetal. I’ll bet you don’t need higher temperature, but the
ability to put out enough energy per second to overcome the high
heat capacity of silver, and overcome the bleeding away of heat from
the edges and corners. Try heating up the corners and outer edges
first, before you ever address the area where the bezel is.

When soldering items that have a lot of surface area, I put a
support* under it, so torch heat can easily flow all around,
including underneath. With thicker gauges, it allows me to address
both top and bottom of the sheet. Sounds like you need to be more
vigorous in heating the sheet - you not only have a lot of surface
area but (if it is 20g), considerable thickness. If I’m working with
a large and/or thick piece, I’ll use the #2 head on my torch. Try a
bigger torch tip if you have one.

Most of the time, the support I use is a flattened wad of 26g iron
binding wire. I take a looooong length, wrap lightly around my
fingers a few times, then cross-wrap until I have sort of a bulging
oval. Then I put it between two steel bench blocks and mallet it a
few times until it’s flat. This gives me a very porous surface with
plenty of support for my piece. It doesn’t act too much like a heat
sink, and prevents the work from sagging.

hope this helps,
Kelley Dragon

One of the things that is easy to forget is that gold needs a
different flux than silver. If you are trying to use paste flux for
the 18K bezel, it doesn’t work very well. Instead, use yellow liquid
flux - it used to be called Griffiths. And easy solder isn’t your
best choice either - use 18k solder.

Judy Hoch

Goss is a Prestolite type brand of air/acetylene torch.

Beverly, a 2" x 2" sheet isn’t that big unless it’s a thick gauge. If
it’s 20 gauge or so, then yes, it can suck up some heat. Either way,
Kelley’s suggestion of a binding wire nest or something that helps
get the sheet slightly up off the soldering block will help. The two
biggest mistakes I see when people are soldering something small to
something larger is that they either don’t give the piece enough heat
(moving too slowly, flame too small, or brick sucking the heat away)
or they have a big enough flame, but in an effort to stay away from
the smaller more vulnerable part like a bezel, they move the torch
around too far outside the edge of the sheet, which means the sheet
isn’t receiving all the heat. That’s an easy mistake to make when
keeping the torch moving quickly.

You’re right to use easy silver solder on the bezel since you’re
soldering it to the silver side of the bi-metal. It will give you
better flow than the 18k solder.

Hope this helps!

Victoria Lansford

That’s not been my experience…paste flux for gold, silver, bronze,