Regarding your post about cleaning gold, you mentioned using a
tinning block used for tinning soldering irons. Tinning block seems
to be sal ammoniac which is ammonium cloride, you said to use
ammonium sulphate.
Please clarify. thanks.
Richard Hart G.G.
Denver, Co.
Regarding your post about cleaning gold, you mentioned using a tinning block used for tinning soldering irons. Tinning block seems to be sal ammoniac which is ammonium cloride, you said to use ammonium sulphate.
Richard, you’ve not named the original poster nor used the original
message subject, so I cannot specifically reference an original
question. But that said, ammonium chloride (Sal ammoniac) has
traditionally been used as a “refining flux”, used to help remove
impurities when melting gold. Generally this refers to baser metals,
like lead, iron, tin, etc, which may contaminate the gold, or things
in your alloy from inadvertently included solder when reusing old
gold. It does not actually behave as one expects of a flux, ie
melting and covering/protecting the metal. Rather, a small pinch is
added after the metal has fully melted. It doesn’t melt, but instead
breaks down, releasing (I think) chlorine gas, or some compound
thereof. Lots of noxious blue smoke generated as the bits of
chemical skitter around on the surface of the molten metal,
evaporating away. Doesn’t take long and it’s gone. It works because
the chlorine aggressively bonds with the baser metals, selecting the
most reactive (baser) metals first, rather than the gold, silver,
copper, etc. These metals form chlorides which happen to be insoluble
in the metal, so the float to the top and slag off, mixed with the
remnants of your regular melting flux.
Don’t do this without really good ventilation. Those blue smoky fumes
are nasty. But it does work to improve previously cracky or brittle
gold. I’ve got references to this use of Sal ammoniac/ammonium
chloride in old books by George Gee in the late 1800s, where he
describes just this use and behavior (though at that time, melting
was done in a furnace, not with a torch as we might do today. He also
mentions plain old table salt (sodium chloride) as having a similar
use, though apparently it’s not as effective. I’ve not compared them
so I can’t say why that might be so, but that’s what Gee’s book says.
If you go to the German web site of jewelry tools supplier, Karl
Fischer, you can find another product used for a similar purpose.
They call it Auropurifax,
and describe it as potassium nitrate. A related product, Argoflux,
also contains this, plus other stuff, for use with carbon/graphite
crucibles. Not sure exactly the difference beyond that. Otto Frei
carries both of these (watch out for the hazardous shipping charges)
Presumably it does something similar, since this is a strong
oxidizing agent, which would also react first with baser metals,
again slagging off the oxides with your melting fluxes. I got a
bottle of this stuff years ago and have been using it up slowly
since. It seems to work about as well as ammonium chloride does, in
my experience which is only a casual comparison rather than any
really good side by side testing. It has the very big advantage of
not generating those noxious blue smoky fumes.
Hope that helps
Peter Rowe
It appears the flux auropurifax is potash. Take a good look at the
label, it’s in German.
AFAIK “auropurifax” is basically potassium nitrate, KNO3; in German,
properly, “kalium nitrat,” altho there may be more archaic
designations still current by useage in a trade as old as this one.
Cheers
Hans Durstling
Moncton Canada
It appears the flux auropurifax is potash. Take a good look at the label, it's in German.
At age 5, I spoke German. Not now. So I’m stuck with needing
translations.
the Karl Fischer web site, however, specifcally says potassium
nitrate (also known as saltpeter). And the description on the Otto
Frei web site says the same (though I’d guess they’re just copying
the Fischer web site. I’m guessing that’s whom they import it from,
though I don’t know…) Potash is an imprecise term for any of a
number of potassium compounds, including potassium nitrate. Potassium
itself is not likely to be the functional agent in the refining
flux, but rather what it’s a compound with. Potassium nitrate is a
strong oxidizer (oxygen source) which would tend to cause baser
metals to form oxides, which generally slag off from a melt. I don’t
know, but I’d guess that potassium chloride, also lumped into the
name potash, might work the way ammonium chloride (sal ammoniac)
does, by similarly reacting with baser metals to form insoluble
chlorides, which also slag off. Whether the actual mix of
auropurifax is only potassium nitrate or a less pure mix of several
potassium compounds, I don’t know, other than to observe that the
bottle contains a pure white uniform crystaline powder, whatever that
means. Some of the other potassium compounds, like potassium
carbonate, would be unlikely, I’d guess, to have any useful
properties as a refining flux. I’d guess that the label in german
may for whatever reason be using a simple generic name, rather than a
more precise chemical name. Not sure why they’d do this, but it seems
possible that they make it with a single pure chemical, but refer to
it with the old traditional less precise name. One can look at a
number of commercial silver oxidizer products that list as the active
ingredient, “liver of sulphur”, but examining the MSDS shows the
active agent to be a more carefully chosen single chemical rather
than the impure mix of LOS. That would be an example of similar
labeling, if indeed that’s what’s happening with Auropurifax…
Peter.
It appears the flux auropurifax is potash. Take a good look at the label, it's in German.
According to the safety data sheet, it contains (as harmful
components)
potassium nitrate
potassium carbonate (potash)
Dinatriumtetraborat (whatever that is in english)
This stuff is toxic, harmful to the environment and oxidising (fire
accelerant), it can harm the fertility of women… usual workplace
safety recommended: Hand and eye-protection, good air ventilation.
Potassium itself is not likely to be the functional agent in the refining flux, but rather what it's a compound with.
Role of potassium in refining is to get rid of metalloid compounds,
which are the major cause of brittleness in alloys.
In this process it is potassium itself which is functional, and the
reason it is introduced in compound form is the difficulty in using
it in pure state. Potassium violently reacts with water forming very
strong base. It is this property of forming strong base that is
important in dissolving metalloid compounds. It is unnecessary to use
in day to day melting and should only be reserved when resulting
alloy is unworkable. It should be noticed that it’s use damages
crucibles.
Sal ammoniac is the way to introduce potassium into melt. Chlorine is
never a desirable component and must be controlled. Correct way of
using sal ammoniac is to mix it with powdered charcoal and use it not
as smelting flux but as cover flux. Chlorine gas is absorbed by
charcoal and potassium is released into alloy to engage metalloids.
It is used with silver alloys primarily. For gold alloys it is not
recommended. It can be used if alloys is heavily contaminated and
must be saved, but it should be introduced in form of saltpetre.
Chlorine should be kept away from gold.
Potassium is the most active metal in the base forming row. Next
metal in the row is Sodium, and #3 is Calcium. It means that these
metal act in the same way, but require larger volumes and more time.
It is not practical to use them in goldsmithing, but in large scale
industrial application, they are much cheaper to use that Potassium
compounds. One of the examples I can think of is the use of limestone
in many flux recipes for bronze.
Leonid Surpin
- Dinatriumtetraborat (whatever that is in english)
Di-sodium tetraborate - AKA borax.
original poster here- yeah, ammonium chloride or ammonium sulphate-
both salts of ammoniium ( a mineral - not an ammonia salt !) Both are
NH4 's, depends on the manufacturer as to their exact chemical
composition ( one is NH4CL, the other NH4SO)- bottom line: Sal
Ammoniac, sold as a tinning block - commonly at stained glass
suppliers is the thing to crush up and add to charcoal ( activated)
to make a refining flux for gold.The ratios I gave originally are
correct.Carles Codina, DX Ross,Harold O’Conner and a host of other
notable jewelers reference the same mixture for a simple refining
flux The stuff Fischer in Germany sells is not at all the same thing
and misses the point I wrote at all - simplicity and cost ! most
people have some activated charcoal around for one thiong or another
(in the studio, aquarium or garden) - the tinning block is under 3
bucks a block - which will make more refining flux than one person
will probably use in a couple of years for smallish melt and pour
open crucible jobs/castings.When ordering the Fischer vended product
consider that the shipping alone from Fischer ( and maybe a hazmat
upcharge too) is more than a bag of charcoal bought at a home store
and a block of sal ammoniac from a stained glass supply or craft
store, plus taxes, the gas to get there and back ( or whatever method
of retrieval you choose.) and any other costs you can associate as
compared to making it one’s self !!! The main thing to remember here
is that it (Sal Ammoniac) absorbs humidity RAPIDLY- store the block
wrapped tightly in plastic or other material and in a non-metal
lidded container, and the small amount of mixture of charcoal and
ammonium chloride equally capped and tightly closed ( a film
cannister with a screw on top works adequately well, a glass rubber
gasketed container better…rer