I see this one pop up periodically. Standard '20 Mule Team Borax"
is Hydrated sodium borate, Na2B4O7 -10H2O at the 99.5% range. The
rest is inert minerals.
Yes it is pure borax, however borax by itself is not a very good
soldering flux. It is ok for higher melting point items like 18k gold
that don’t need much in the way fo flux protection anyway. Borax
works ok for a basic casting flux. Adding boric acid to borax will
lower the temperature where the flux becomes active and make a much
better soldering flux.
A nice way of using a solution with Borax and water is to mix borax
with hot water, shake well and let it cool of. The obundant borax will
cristalize on the bottem of the jar. Poor the liquid solution of and
you’ve a perfect inexpensive solution against firescale.
After watching many jewellers and novices, I’ve seen that people are
using a way to much of flux! Some of them are using it in the way to
learn a metal swimm in flux I quess. The proper way of using a flux
is to preheat your metal first then aply flux (with a brush) where
the flux immediatly evaporates. A thin white layer of powdered flux
should be visable and that’s it. No more no less.
I still experience that many goldsmiths are pooring there flux on
their workpiece, heat the metal “cooking” their flux and then place
their solder on top of it. Some of them like to see their solder dance
by laying their solder on top of the wet flux. One whould be amazed
how often this happends! Other once apply a tick layer of powdered
boric acid (about 2mm and I’m serious know!).
By all means, I’m not correcting anyone or shooting arrows but there
is a better way of using flux and this way can be one of them saving
you a few bottles of flux a year. Feel free to perform you
solderoperation the way it works for you.
I find that high boric acid consecrations not very good for casting.
It’s too sticky and often follows the metal into the mold. displacing
the metal and leaving areas filled with the boric acid flux, rather
than than the metal. Straight borax powder does a better job.
So what’re in those ‘borax cones’? I still have the one I used in
London all those years ago. A bit of spit in the slate, a grind or
two with the cone, and it worked just fine. Never had any trouble
with it not going active until it was really hot, and sterling
isn’t known for being forgiving about lack of active flux.
But it’s solid, not a boric acid slurry, so my assumption was always
that it was simply a cone shaped lump of pure borax.
My assumption is it is just borax but I don’t know for sure. But if
it is then it doesn’t melt till it is at 1369F 743C. This is why
boric acid is added to fluxes because it has a much lower melting
point at 340F 170C.
I still have the one I used in London all those years ago. A bit of
spit in the slate, a grind or two with the cone, and it worked just
fine. Never had any trouble with it not going active until it was
*really hot*, and sterling isn't known for being forgiving about
lack of active flux.
With hard silver solder you are real close to the melting point of
borax so not too big a deal, medium and easy are a different story
and industrial solders with lower melting points are just not going
to flow well with a straight borax flux. This is why fluxes like
Handy Flux are designed to melt at about 1100F so that the lower
silver content solders will be able to flow and wet the metals being
joined.
I still experience that many goldsmiths are pooring there flux on
their workpiece, heat the metal "cooking" their flux and then
place their solder on top of it.
The step that you describing as “cooking the flux” is done to create
what is know as borax glass. If this is omitted and parts are small,
they could move during soldering.
Some of them like to see their solder dance by laying their solder
on top of the wet flux. One whould be amazed how often this
happends!
There is very good reason for that as well. For solder to be drawn
into joint, it must be placed correctly. Solder must touch both sides
of the joint. Watching flux bubble, (dance) allows goldsmith to judge
solder placement.
Other once apply a tick layer of powdered boric acid (about 2mm and
I'm serious know!).
Thick layer of boric acid, either pure or in combination with borax,
is used to insure that previously soldered joints would not come
apart. Thin layer of borax enhances flow of the solder, thick layer
inhibits it.
I find that high boric acid consecrations not very good for
casting. It's too sticky and often follows the metal into the mold.
displacing the metal and leaving areas filled with the boric acid
flux, rather than than the metal. Straight borax powder does a
better job.
If alloy has zinc or nickel in it, use of boric acid in flux
formulation is very desirable. For yellow golds, borax does work
better. However, it can also follow metal during the pouring. To
combat this tendency, powdered glass is used as an additive to flux
formula.
The step that you describing as "cooking the flux" is done to
create what is know as borax glass. If this is omitted and parts
are small, they could move during soldering.
I know Leonid, what I ment is that some are realy drowning their
workpiece in flux by using a seringe or other tools. I believe this is
an overkill and waste of flux…that’s what I’m trying to explain.
I’m well aware of the use of borax glass.
There is very good reason for that as well. For solder to be drawn
into joint, it must be placed correctly. Solder must touch both
sides of the joint. Watching flux bubble, (dance) allows goldsmith
to judge solder placement.
Their is a way of moving a bit (1/10 mm) or jumping (2 and more mm)
around like shivering and shaking. Hard to explane in another
language then your own one. When solder is placed correctly from the
begin it will not move much as the flux act’s like a glue more or
less (sticky might be the proper word).
Thick layer of boric acid, either pure or in combination with
borax, is used to insure that previously soldered joints would not
come apart. Thin layer of borax enhances flow of the solder, thick
layer inhibits it.
Temperature control, binding wire and other tricks are more reliable
then meltable flux in my believe. However, feel free to work as you
like.