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Pores in soldered joints


#1

Hello everyone,

So lately i’ve been soldering joints and for some reason after i’m
done soldering i’ll notice that there are tiny pores on the sides of
my rings. This happened on gold and silver rings after I had sized
them. I usually clean the joints pretty well and dip the rings into
boric/denatured alcohol, add flux then solder(medium), and apply
heat. Any suggestions on what I can do differently? any help would
greatly be appreciated.

  • Sincerely, Jimmy

#2

Jimmy- It looks like you are prepping your work properly. Are you
using paste flux or liquid? I’d recommend paste.

Usually porosity in solder seams is from over heating the solder thus
"boiling out" the lower karat metals that were alloyed with the
solder. I always wait until the object I’m soldering is at solder
temp and then at the last second add the solder to the inside of the
seam. I prefer to use the highest temp solder I can to help avoid
this issue. Lower temp solders tend to show pits more than higher
ones. because it’s easier to over heat them. Have fun and make lots
of jewelry.

Jo Haemer
timothywgreen.com


#3

I’ve suffered the same at times, and it is apparently a symptom of
over-heating during soldering. If you overheat the metal, one or
more of the lower temperature metals in the solder alloy can
evaporate, creating the pores.

Helen
UK


#4

Pores, or pits as some people call them, in my experience usually
occur for two main reasons: a dirty soldering station, or heat from
my torch - either too much or too long. I usually start by cleaning
my soldering area. I dump out my boric acid/alcohol solution, clean
off my soldering slate, empty my solder flux jar and get fresh flux,
and completely clean all my soldering tools like tweezers and picks
with soap and water. I also try to be more patient when I re- solder
my piece and not try to heat the work too fast or for too long. I
also always try to use the highest melt point solder I can in the
event that I have to go back and solder in the same area of the
piece. I have found that medium and easy flow solders pit more
often.

Hope this helps


#5

Hello,

Zinc is the metal to put the blame on.

People used to call it “zinc gobble” or “zinkfrass” (german) Zinc
starts to oxidize -at high temps- leaving pits behind in a joint. As
others already mentioned, this is caused by overheating and/or
extended soldering procedure.

For the ones who make their own solder, zinc gobble may be caused by
incorrectly melting of your metal ingredients.

Roll the material to thin pieces and cut them in small pieces, heat
your (boraxed) crucible and then insert the solder.

Cover it with a mix of charcoal and salt. Melt your solder quickly
(!) Poor an roll to the wanted thickness. This results in a fine
solder of good quality.

Adding a few flakes cadmium can help aswell (which I don’t recommend
for beginners due to the toxicity of cadmium). Cadmium prefends the
oxydation of zinc according a recipe I have from older books. Only
work in a very good ventilated room and take precautions needed for
cadmium!

Have fun and enjoy
Pedro


#6

All solder seams have some gas bubbles or pits in them, the problem
comes when they are too big or too numerous. There are two main
sources of the bubbles, absorbed gas being released as the molten
solder cools or vaporization of zinc or other low boiling point
metals. Cadmimum which is getting less likely to be found in solders
has a boiling point of 1413F which could cause problems with vapor
off gassing but most silver and gold solders now contain zinc
instead of cadmimum and it vaporizes at 1665F so most silver
soldering will not have bubbles from zinc vapor as you would be darn
near the melting point of sterling at 1665F. And with the exception
of high temp white gold solders most gold solders are fluid below the
vaporization temperature of zinc. So the big culprit is oxygen from
the fuel gas being absorbed during the heating by the molten silver
in the solder and then coming back out of solution as the silver
cools. Copper and zinc the other metals in silver solder do not
release oxygen on cooling but form stable metal oxides. Hydrogen
from the fuel gas can do something similar in copper and other metals
used in solder formulations as they cool the hydrogen comes out of
solution.

As mentioned by others overheating or prolonged heating will increase
the number of bubbles due to greater absorption of gasses.
Insufficient flux or too oxidizing a flame can also be problematic
for the same reasons.

James Binnion
James Binnion Metal Arts


#7

Thanks for the James. I didn’t know about the zinc.
Probably still a good idea to use hard solder though. Sheri


#8

I might add, solder does not cross (relatively) large gaps well. The
tendency to have pits increases with larger gaps. One needs to be
able to employ strategies of configuration whereby these gaps can be
minimized. Close fits are of primary importance. Long solder seams
are more problematic too.

David L. Huffman