Brass disintegrates during sweat soldering

Jewelry Discussion
1

I’ve been working with sterling, brass, copper and other metals for
years, and for some reason, I’ve never encountered this before. I’ve
done some research and reading, including searching these forums,
and can’t find an answer to why this mysterious reaction is
happening.

Recently, while I was teaching a soldering class, I demonstrated
sweat soldering a copper wire spiral and some small brass disks (Rich
Low Brass, melts at 1877, 85% copper, 15% zinc, from Metalliferous in
New York, 1/16" and 3/32" in diameter, cut with a tiny disk
cutter/punch) onto a sterling 1" disk. The demo was for beginners, so
we used easy solder and I set up everything as usual. I applied
solder first to the underside of the brass disks and copper wire,
placed them on the sterling disk and heated the whole piece from
underneath until soldered. For this demo, I held the sterling disk in
air with a third hand. Because this class is meant for people to
practice at home, I used a micro-butane torch.

The copper soldered down fine and the brass dots started too as
well. But suddenly the brass dots just started for lack of a better
word, disintegrating. The sterling was fine. The copper spiral was
fine. They weren’t even glowing, since I was holding the temp at
around the flow point of the easy solder. The brass dots never even
showed any color. And the brass dots are floating in their own molten
blobs, melting out from below, leaving thin skins of brass on the
surface. I haven’t seen this before, so I held the temperature a
little longer. Eventually, even though the sterling never even came
close to a visible red or orange heat, one of the dots ate right
through the sterling below it.

I tried another piece of the same brass on a piece of sterling, no
copper, set it up again and got the same results. I’ve done the same
demonstration with exactly the same dots in copper, and that strange
melty metal thing never happens.

In another class, one of my students used dots of 24 ga. patterned
brass, also from Metalliferous to solder a texture onto a sterling
blank for a ring. The dots sank into the sterling and disappeared,
leaving round craters as if they had etched into the silver.

Any ideas? Even after 17 years of jewelry, there’s always something
new to learn. This one is bizarre and doesn’t seem like a normal
reaction to a simple soldering. Maybe I’ve just never encountered
something that other jewelers like you guys have experienced before.
Unless the rich low brass is not the alloy they claim? So far, I’ve
only seen the reaction with the Metalliferous brass. I’m looking
around for a piece of brass from another source to try.

Anyway, I’d love to have some sort of explanation to offer for this
little mystery. Your help is appreciated.

Joe Silvera

2

I’ve been eagerly awaiting someone’s answer to your question, as I
seem to remember there is some metallurgical chemistry when soldering
with brass. So while waiting I did a search. Check out this thread,
it may offer some insights.

Any other explanations for this?

Carla

3

When you are joining dissimilar metals you will initialy form a
diffusion bonded alloy at the junction point. This will have a
melting point lower than the melting point of both base metals. The
initial fusion will be at the eutectic point ( the lowest melting
point possible with the components) of the mixture. With binary
components - for example silver and copper only. The eutectic point
temperature is C.

Fusion begins with diffusion bonding which is the basis for
granulation, Kumbo, and Mokume.

and sintering (powdered metal fusing and in ceramic glazes. Diffusion
bonding requires intimate contact, clean surfaces and time at
temperature.

There is a minimum temperature point required for metals to begin to
bond. This is called the Tamman point. This is not a totally well
defined temperature but is determined to be about 50% to 65% of the
absolute temperature ( absolute zero based ) at the melting point of
each component.

The range will probably eventually be determined much more closely
but it can be difficult to measure.

As the materials reach this point they can bond but the reaction rate
is very slow but as the temperature increases the reaction goes
faster and faster in a non linear relationship.

The best explaination of the Tamma point that I have seen is in the
Australian magazine " Ceramics Technical" NUMBER 12 2001 PAGE 52 -54.
This is based on ceramics glaze formation not metallurgical
applications but the principle is real. In metal fusing the correct
tammin temperature may be close to the metal oxide melting points
than the pure metal based ones sincc you will never have pure oxide
free surfaces. you will not also have true intimate contact all
over. yopu can ee a little more with a goggle search but it maqy not
be easuy to viualize or interpit.

In the case of fusing brass to silver esspecialy you re forming a
lowest melting point of the comibonation at the joint. You have to
come up to fusing temperrature from the largest mass and not get too
hot.

PLACING HEAT ON TH LOWEST MASS PARTS\WILL CAUESTHE METALSTO FUES
RAPIDLY AND OVERSHOOT. THS CAUSE ALL THE LOWMASS MATERIAL TO SINK
INTO THE LARGER MASS. DEP[ENDING ON ALL THE VARIABLES THIS CAN BE
VERY FUSSY. YOU \ARE MAKING AN\ EASY OR EXTRA EASY SOLDER AT THE
JUNCTIONS.

In a furnace brazing situation the variables can be controled BETTER
and a process developed. TORCH BASED FUSING IS VERY DIFFEREB NT and
will be regulated bny skill and experience.

4

I’ve made brass jewelry for 30 years and have never had the problem
you mention. Mainly, I have to be careful when I work with silver,
not to melt it because I’m used to working at higher temperature (for
brass, copper, and nickel-silver).

When I first read this, I thought you probably just had gotten some
wonky brass. I buy my sheet and wire from Rio Grande and Indian
Jewelers Supply, except for the heavy wire (4 and 6 gauge) which is
available only from Metalliferous. Some years ago, I bought some
wire solder for brass from Metalliferous, and it was useless –
wouldn’t flow. Recently, I bought some of their brass sheet solder
and it seems to be OK.

I’ve done sweat soldering without problems, except when I wanted to
re-do an area. I have no metallurgical answers for any of this.

Judy Bjorkman

5

Hi…my son called it “subduction” when the 14 Kt sank into the
Sterling Silver!

Rose