Solder is inferior metal from the point of view of structural
engineer. Previously, I mentioned Brepohl. Brepohl also gives very
good introduction to properties of precious metals. Did you ever
wonder why are we using 18k and not 17.5k or 18.5. Not to make
thing overly complex, but if one alloys gold, silver and copper,
there are only 3 combinations which have good mechanical properties
and they are 18k, 14k, and 9k. Slight variations makes a lot of
difference in mechanical properties.
Nope. Sorry. We use (normally) even karats by convention, habit, and
in many places, law.
Originally, the even karats were what goldsmiths used because they
were the easy alloys to make. 18K is 18/24 (or 3/4) gold, so it was
easy to do the math. Equally so with 22, 14, 12 and 9K. Keeping in
mind that the 24K system goes back to the middle ages, when most
goldsmiths couldn’t read, let alone do figures. Also keeping in mind
that the simple concept of arabic numerals didn’t come into wide use
in the west until the 1200’s. Just try working out the math for a
complex alloy using only roman numerals. (Roman numerals have no
concept of decimal places or “zero”, for example…)
Since the karat alloys you mention predate such simple concepts as
arabic numbers, what’s the likelihood that they were chosen due to
any systematic search for ideal mechanical properties? None. They
were chosen because they were easy to make.
Now they’ve become codified in law in most places. In the UK, you
can (if you want) use 14.5K, or any other silly number you want, but
it’ll still hallmark as the next lower karat, so there’s no
financial point in it. Since it’d just be a waste of money, the
refiners only produce metals that work out to the legally required
By way of example, there is an alternate silver standard in the UK:
Britannia Silver. Instead of 925/1000 Ag, it’s 958.3/1000 Ag. It was
used (briefly) during the reign of Queen Anne, and has been retained
ever since. The way they got that particular percentage was 958.3 was
what resulted when the silversmith melted an ounce of fine silver,
and then threw in a certain number of grains of copper per ounce. The
sterling standard at.925 resulted from a similar formulation. Both of
those alloys were chosen for standardization because they were easy
to make, rather than any other reason.
About term brazing. Silversmiths, most of the time, cannot fit
joints to required precision for capillary action to take place.
It is not a putdown. As size of joint increases, the level of
difficulty of obtaining good fit grows exponentially, so
silversmiths solder by heating joint with torch and simultaneously
supplying solder from the rod, known as brazing rod and technique
Nope, it’s normally known as “stick feeding”, and is metallurgically
identical to the action of the solder if placed into the joint in
pallions. Namely: brazing.
What about mechanical strength you may ask? Different schools of
silversmithing handle it differently. English formulated their
solder with understanding that there will not be any capillary
action, so formula was designed to increase strength. French
increased purity of their silverware. Hallmarked french silverware
is not 92.5 percent silver, but 95. Some German guilds used 80/20
and employed gilding, and etc.
Please see above: sterling resulted from easy math. As did 80/20 and
.900 coin silver. The need for a stronger/cheaper alloy than pure
silver was genuine, but the regarding the actual alloy percentages
chosen, those came from easy math.
Regarding our discussions of Brepohl, I emailed Charles Lewton-Brain,
the man who wrote the translation you cited, asking him what term
Brepohl used in the original, and whether or not he’d translated it
as “solder” in the English to save confusion. I also asked both
Charles and a Swiss goldsmith of my acquaintance how German talks
about “soldering” in the goldsmithing sense. The text of Charles’
Ok, I went to look and read the pages. Essentially he defines it
all as l__ten (soldering), hard and soft. in all cases the
material melts, flows in the seam by capillary action and diffuses
into each side of the join. If the metals being joined melt then
one is welding. He then discusses soft soldering, talks about the
negatives, what it is used for and that the 'aformentioned
diffusion is very limited', so he does consider some diffusion to
occur, but almost not noticiable.
so, its all soldering in Germany. But that does not mean that it
is all soldering in English, different language, culture,
concepts... And is it a goldsmithing book, so an engineering text
might have a different take on it.
Essentially the difference appears to be the temperature range at
which it occurs and the degree of diffusion that can occur.
So. It looks like the confusion starts with the original German,
which doesn’t distinguish between soldering and brazing the way
English does. It just talks about hard and soft soldering, much as
American jewelers always have. (I’m betting we picked up the habit
from immigrant German jewelers.)
You will note that the man who wrote the translation you cited
(kindly) re-examined that section of the original text, and came to
the same conclusion as the rest of us: in English, the distinction
has to do with temperature.
As far as diffusion (and capillary action) goes, Brepohl’s talking
about it happening on an inter-crystalline scale, which is vastly
smaller than any joint you or I could make. Thousandths of a
millimeter or less. At that scale, it’s not just silversmiths who
can’t make a tight joint. No human could.
As long as we’re on the subject of books, might I recommend to you
Mark Grimwade’s “Introduction to Precious Metals” (2nd edition). It’s
an entire book devoted to the metallurgy of the precious metals,
written by one of the foremost precious metal metallurgists of our
generation. It was recently rewritten and re-released with loads of
fascinating about not only karat gold alloys, but also
brazing alloys. For example, (from page 166)
"It is important to draw a distinction between the terms soft
soldering, hard soldering and brazing. By convention, soft
soldering refers to joining by soldering at temperatures below
450CB9Ac, whereas hard soldering is soldering above that
temperature. The dividing line is somewhat arbitrary and it
arises from the fact that soft solder alloys have relatively low
melting ranges and hard solders have much higher melting
temperatures. "..."Hard soldering at higher temperatures,
typically above 600CB9Ac, is known also in the engineering
industry as brazing and, hence, these alloys may be known as
brazing alloys because the original alloys were based on
copper-zinc. (brass.) The principles of soldering and brazing are
the same and because jewelers have traditionally used the term
soldering instead of hard soldering or brazing, this will be
followed throughout this chapter where applicable."
He then goes on to list several pages of fascinating information
about joint design and the metallurgical behavior of hard solders. I
recommend it to your attention.