I have been using 14k yellow gold solder to solder both 18K
joints and 14k joints. I used it on the 18k seams because I had
read in a book by Robert von Neuman to use lower karat solder to
make seams.
J…S., I’ve not gone and looked it up again, but i’ll bet the
comment in RvN’s book was a reference to an old trick of using 14K
gold to solder 18K, or 10K gold to solder 14K, etc. This simply is
based on the observation that for a similar color, usually the lower
karat golds melt lower than the higher karat ones, thus the lower
karat golds can, in a pinch, be used as solders for the higher karat
ones. But understand that this is merely an old cheapskates trick
from the days, perhaps, when solders were not as sophisticated and
available as they now are. Remember that RvN’s book isn’t exactly
recent info. And he’s talking about the basic gold alloys being used
as solder, not saying you should use a low karat solder to work with
high karat gold. Your solder grade should be matched to the karat
you’re soldering. Use an 18K solder to work with 18K. It’s designed
for optimum performance in this role. Likewise, use a 14K solder to
work with 14K. To get the best color match, use the harder grade
available (highest melting point of that karat). Lower karats, or
lower temperature ratings for a gold solder, generally mean the color
will be a poorer match. While there may be times, in repair work,
where you’ll need to drop down to a lower karat solder than the work
your soldering, this should only be done when you really must have
that lower melting point. Even then, often there are extra easy
melting solders available which can still be rated for the right
karat, and get the job done for you.
Also, it’s important to discuss the types of solder as well. Aside
from the myriad available karats, melting points, and colors of
solders, there’s also a basic division between so-called 'repair"
solders, and “plumb” solders. Repair solders are intended to be
easier flowing, for easier repair of items which may be especially
fragile, etc. The karat content isn’t considered so important, and
these solders generally are a lower karat than the work for which
they’re designed. The Plumb solders, however, are made with the same
gold content as the work for which they’re designed. To get the
lower melting points, compositions may have to differ from the gold,
so sometimes, though the gold content is higher, plumb solders
sometimes don’t match color as well. Repair solders sometimes can be
a better color match, but then are lower in gold content. Note that
I say sometimes. With plumb solders, your higher temp ratings are
usually the best available color matches, as well as producing the
best joints.
Note too, that solders from one manufacturer may differ markedly
from those of another manufacturer that may be labeled the same
grade. Buy from several, and test them out. They’ll vary in color,
how well they flow, exactly what temps they flow at, and strength of
the joint.
Peter