On Sun, 27 Aug 2006 09:07:43 -0700, in rec.crafts.jewelry "Paul WIlson"
Post by Paul WIlsonAs to the cleaning of jewlery during processing (removing investment,
You have a number of different tasks here. They do not require the same
treatment.
INVESTMENT
Investment is best removed either with a chemical agent that will do so, or
mechanical help, such as from untrasonic cleaners or steam cleaners. In an
ultrasonic, Any ordinary jewelry cleaner, or for that matter, commercial
cleaner like Top Job or Mr. Clean, will do the job. So will plain water, in the
end. But the commercial investment removers work faster, and can work without
the ultrasonic. There are several types. Most are either mild acids, most
commonly dilute hydrochloric acid, or Citric acid (I know one guy who just uses
lemon juice, straight from the bottle. Seems weird to me...), or strong
alkalis, like quite concentrated sodium or potasium hydroxide. These latter are
more dangerous to use, but will also work with some of the trickier to remove
investments, such as those used for platinum. The most aggressive investment
removers are those based on hydrofuoric acid (which literally dissolves silica),
allowing them to remove even the toughest most highly sintered silica
investments. But these are quite dangerous, to be used only with very good
ventillation, like a commercial grade fume hood. Note that home brew mixes for
investment remover may not work as well as the commercial, since these generally
are not just plain chemical dumped in solution, but a more complex mix of
several chemicals that interact. Especially true of the caustic versions. I
recommend buying the commercial products, rather than using home brew, if you
need the caustic types. But for my own needs with standard investments like
Satin Cast 20 or other gold/silver investments, I usually just use whatever's
handy (plain cleaner, not fancy investment remover) in a seperate beaker in the
ultrasonic (the seperate beaker means the removed investment doesn't muck up my
ultrasonic for normal cleaning, making the process itself cleaner)
GREASE/OIL/POLISHING COMPOUND/DIRT
Grease is best removed by degreasing agents. Normally known as soaps and
detergents, or various solvents like acetone, or strongly alkaline agents like
cauistic soda or lye, etc. . None of the agents you list will have any effect
on grease or oil or waxy stuff like polishing compounds. You simply need an
actual cleaner. Normal household cleaners like Top Job, Mr. Clean, or a slew of
others, especially those with a bit of ammonia, will do fine. Avoid those with
bleach, as that can damage some metals. Heating the cleaning solution will do
wonders to improve the results. For some needs, electrocleaning is especially
useful. For that, a strong alkali (sodium or potassium hydroxide again) is used
to make up the solution. Electrocleaning is useful when you need to get a metal
surface actually chemically clean. Most cleaning agents in an ultrasonic will
get things to LOOK clean, but there may still be a molecular level film of
contaminants. Some commercial cleaners contain lanolin, for example. to be kind
to hands. Jewelry cleaned in that will look bright and sparkling, but don't try
to electroplate over it. And steam cleaning, while good, can also still leave
traces of contaminants.
Normal cleaning of dirt and grease is very effectively done with an ultrasonic,
using the above cleaners, or commercially sold cleaners made for ultrasonic use.
These are more effective, since their surface tension and chemistry is balanced
to optimize the operation of the ultrasonic cleaner, maximizing cavitation. So
you may prefer them, especially for higher volume use where just leaving things
in the cleaner longer may not be desired.
Before the days of ultrasonics, most shops used what was, and is still, called a
"boil out pot.". As the name implies, just a container kept at a near boil, an
nice hot simmer, on a hot plate or a stove burner or something (or use an
electric crock pot) That's filled with a strongly alkaline cleaner. The
classic was just lye (sodium hydroxide), perhaps with some ammonia added. That
will remove even the toughest polishing compound build up after buffing, or
will clean years of gunk from behind the diamonds on that ring you need to clean
before you can repair it. Works fine. use with ventillation. Takes longer
than an ultrasonic, but in some cases, is safer for the jewelry (ultrasonics are
actually quite aggresive to the surfaces they are cleaning. Some softer metals,
like cast sterling silver, can be damaged if left in too long.
If a boil out pot with lye is too aggresive for your tastes, and you want
something safer, use TSP, or just plain machine dish washing powder detergent
like Cascade (which is mostly TSP). Slower still, but what's your hurry?
OXIDES, (FIRESCALE/FIRESTAIN)
Oxides generated by heat, are a common cleaning task after soldering or
annealing, or to be removed from castings, etc. Oxides generally are removed by
acid agents. Generally, in many operations where we're removing oxides, we're
also removing soldering flux residues too (though plain hot water will often do
that)
The classic is Dilute sulphuric acid. It has safety concerns, but it's very
effective. For deep penetrating oxides like fire STAIN on silver (not the
surface black oxides) the classic acid is dilute nitric, actually etching down
into the surface.
A safer substituted for sulphuric acid are the commercial pickles like Sparex.
(Sparex 1 and 2 are not the same. Use 2 for precious metals. 1 is for
descaling steel, if I recall right. Might be wrong on that). Personally, I
detest the Sparex brand of this stuff, since what they package and sell seems
likely to be an industrial byproduct, not pure chemical. It's always got this
brown waxy gunk mixed in that makes a mess of the pickle pot. Instead, buy
almost any of the competing products from other brands, or just get the plain
chemical, Sodium Bisulphate. The easiest source, at least for me (and the
cheapest), is my local hardware store. They sell Sodium Bisulphate in a nice
clean, mostly pure (they add de-caking agents, which don't affect use) as a
chemical to be used to lower the ph of swimming pools and spas and hot tubs. The
products are generally given names like ph-down, or Spa-down, or the like. Work
very well, and don't mess up your pickle pot. The main differences between
Sulphuric acid and Sodum Bisulphate is that the latter does not generate nasty
corrosive fumes, and is somewhat less aggressively corrosive when spilled. But
it will still eat holes in clothing, stain wood, and is dangerous is splashed in
the eyes, etc.
One occasionally very useful variation on sodium bisulphate is for use in
removeing a copper colored layer left on brass or bronze after soldering, when
the zinc or tin in the surface has been oxidized and removed, leaving just
copper. To get back to the proper brass color, or to remove copper "flashing"
left on silver due to contaminating pickle with iron or the like, Get some
concentrated hydrogen peroxide. Not the very dilute disinfectant from the drug
store, but the 20 percent or higher stuff used in hair care. It's caustic, so
treat it with respect. Mix up some fresh sodium bisulphate pickle, and add a
bit of the peroxide. The resulting pickle will remove the copper flashing. It's
aggressive, so don't let things soak longer than needed. The solution degrades,
and must be mixed fresh for each use (well, it keeps for a few hours, but by the
next day, will mostly have lost it's activity, when it can be added back to your
regular pickle (the peroxide will be gone)
Safer substitutes for sulphuric acid or it's salts (sodium bisulphate) can be
used, but are much slower. Alum is one. it's also quite useful for removing
broken drill bits from silver or gold or platinum. Used hot, it will pickle
gold and silver oxides. But slower.
Even slower yet, but also still effective, is Citric acid. This stuff is
popular with jewelers who've got small children around, as it's actually pretty
much not a safety issue at all, at least not in the concentrations usually used.
Effective use of Citric acid usually depends on good technique with fluxes to
prevent excessive oxidation in the first place. Heavy fire scale can be
removed, but it takes a long time, and may require a bit of mechanical abrasion
as well, with citric acid. Citric acid is also a basis for some of the milder
investment removers. They guy I know who does that with lemon juice came to
that use after noting the main ingredient in his investment remover...
Vinegar and salt. Vinegar by itself is just not very effective at removing
oxides. With salt added, it does become a bit more active, especially on
copper. it's a classic cleaner for windows, (without the salt), or with the
salt, for removing mild heat discoloration on copper cookware. But for removing
serious fire scale from gold and silver, you'll find the results somewhat mixed.
it's not totally inactive, but it's also not all that effective either. And it
will do nothing at all for deep oxides like fire stain (but then, neither will
the others until you get to nitric acid etching/bright dipping) Note that
vinegart and salt can also be somewhat unpredictable. If not rinsed, on some
copper alloys, residues will sometimes result in unexpected patinas forming,
especially if the item later is cleaned in anything with some ammonia added...
Plus there's the whole thing about needing to actively rub the surface in order
to get the salt/vingar solution to work. Makes it less useful for anything with
details. You need something that works well with just a soaking action. If you
find yourself with no proper means of doing this, and have the vinegar and salt
handy, then use it. Better than nothing. But understand this is not the easy or
effective way.
Personally, I'm not patient enough or desperate enough to bother with vinegar
and salt. I prefer these on my salads. For jewelry use, I use the much more
effective agents mentioned above....
Post by Paul WIlson1) sulfuric acid.
2) sparex (#1 or #2)
3) alum solutions (100g/l warm)
4) vinegar and salt (rubbing with a cotton swab)
OK, so it seems the fastest, cheapest and safest way is direct cleaning with
vinegar and salt. If that doesn't work, then go with alum.
Why not? There must be a catch.
The main catch is just that it doesn't work all that well. Alum is better, but
slow. if you don't want the sodium bisulphate, which is the best agent for
this, use citric acid. Safer.
Post by Paul WIlsonWhat about in preparation for soldering? Will vinegar/salt work well enough
to clean articles prior to soldering?
You're confusing cleaning with chemical removal of oxides. Before soldering,
the normal cleaning methods or mechanical, not chemical. You're not usually
trying to etch or dissolve oxides before soldering. Rather, you're cleaning
dirt, grease, oil, etc. Different agents. And with soldering, mechanical
abrasion methods have the advantage of roughing up the surface slightly, which
for some uses can aid in soldering. just a bit of steel wool, or fine emery, if
your metal needs it, prior to soldering. Of course, it should also be free of
grease and oil and other dirt first. Detergents are good for that. Vinegar and
salt are sort of silly for that.
HTH
Peter Rowe