Back to Ganoksin | FAQ | Contact

Cracking 14k red when soldered to platinum


#1

A bid for help with a platinum/14k red gold project. We have
soldered to a 6mm wide band ( ring) thinner (1.5mm )boarders.,
Ther red gold was cast from gold, cooper, silver alloy and looked
and acted just fine untill we soldered the boarders to the platinum
with 20k white. Hairline cracks appeared- some larger than others.
we desperatly tried to repair the cracks via burnishing, and then
flowing ( or rather gobbing) 14k red easy solder. More cracks
appeared. The piece was air cooled through-out.

What did we do wrong? After grazing through the archives- I saw
that 20k white seemed to be the apprpriate solder… We suspect the
difference in melting points causing varying contractions in the
different metals may be the culprit… I remeber reading that Doug
has been working with plat and red gold. Any clues Doug? Should I
use 18k red to reduce a few more degrees between the metals? Any
tips would be much appreciated…Thanks to all for your various
experiences.

Rona


#2

I’m just curious. This is a good metal alloys issue.

Did you mix your own red alloy? This sounds like an alloying issue
with the red gold and not soldering technique.

I just thought of something. Was the crucible you melted the red
gold in ever used for melting silicon gold (the gold that casts up
without oxidation)? It’s just a thought, as silicon increases the
grain size, and makes for gold that can crack while being worked. I
personally have experienced issues with silicon gold such that I
prefer to keep it out of my shop entirely.

I’ve done a lot of soldering with various colored golds and haven’t
seen this problem, although I certainly have seen some weird results
with cu/au combinations, like a high karat red gold that was so hard
when I dropped the ring on concrete it broke into many pieces! Copper
has problems with oxygen, it absorbs about 20 times it’s own weight
in oxygen when molten IIRC, so some zinc is usually used as a
deoxidizer. Perhaps an alloy with the addition of a small amount of
grain refiner would help as well.

Jeffrey Everett


#3
 More cracks appeared.  The piece was air cooled through-out. What
did we do wrong?  

You air cooled. Red golds must be quenched to prevent brittleness
and cracking. The thing that makes this tricky is that plat. likes
an oxidizing atmosphere, and red gold likes a reducing one. Plat
hates fluxes and red gold loves them. I think the cooling is the
real culprit here, though.

Spike Cornelius, Portland, Or. RC ArtMetal


#4
    You air cooled. Red golds must be quenched to prevent
brittleness and cracking. The thing that makes this tricky is that
plat. likes an oxidizing atmosphere, and red gold likes a reducing
one. Plat hates fluxes and red gold loves them. I think the cooling
is the real culprit here, though. 

14k Red is not generally a problem in the air cooling regard, 18K
definitely is. For this job I would use a 14k white or better yet
a 18k yellow solder for this. We don’t normally do red rails to
platinum rings but we do the platinum rails to various colored golds
including red. I would stay away from the 19K white as it is too
hot for the 14K red. The 19K white is liquid at 1640F which is
within 50 to 100 degrees of the melting point of the red gold so
your temperature control must be excellent and a full seam all
around the ring is a large joint that is easy to over heat. My guess
is you overheated the red and it lost its structural integrity.

This is a difficult solder job due to the differences in thermal
expansion between gold and platinum often these joints will crack on
cooling no matter how they are cooled. So a highly ductile solder
will help a lot, which is why I suggest using 18k yellow hard. Also
a stress relieve anneal at 700F for 30 min after soldering will
help.

Jim