I am a water metal detectorist and as such find many silver chains
and rings that have been in salt water. They have a heavy silver
sulfide tarnish that can only be removed with a 10/15 % solution of
nitric acid,this leaves the piece pitted and practically
unpolishible. What type of professional vibrational tumbler and what
polishing solutions are necessary to make these pieces look like new
so that they can be sold.
Thanks in advance,
William
First off, try Sparex instead of nitric - maybe you have, but nitric
acid dissolves silver with ease. Much of your pitting is coming not
from the aging but the treatment. Even maybe try some other things,
like Naval Jelly or instant tarnish remover (the pink stuff - used
to be called “Tarnex” on TV), which works great. Silver really
doesn’t belong in nitric unless you are etching or bright dipping,
which is 30 seconds. Putting chains in a tumbler is a very bad thing
to do, unless they are big curb link ID bracelets. You are going to
get a tangled mess of (still pitted) chains. Even though there are
grinding operations in tumblers, putting a chain through it is not a
good idea - it is an indescriminate thing. By the time the pits are
gone, the chain is gone, too. Unfortunately, since each chain is
probably worth $5-$10 or even $20, and you will never ever get them
back to “new” condition - clean, maybe, but not new, you might just
send them to a refiner and take the $50.
First off, try Sparex instead of nitric - maybe you have, but nitric acid dissolves silver with ease. Much of your pitting is coming not from the aging but the treatment. Even maybe try some other things, like Naval Jelly or instant tarnish remover (the pink stuff - used to be called "Tarnex" on TV), which works great.
Not exactly Ag chains…but might apply…
One of my other afflictions than gemstones/jewellery is ancient
coins…
I have had great results with some horribly spotted items…by
soaking in household ammonia…sometimes monitoring on an hourly
basis…rinse with dish detergent and scrub gently with a
toothbrush…and then back in again…
Minimal or no pitting, but a grey shadow often left…
I leave the grey shadow…I can’t bring myself to polish a
coin…Maybe a swipe or two with a Sunshine Cloth (BTW…buy
several, you will never regret the investment,they are really a nice
adjunct…no connection…)
But I’m not purist enough to allow the splotches to hide the
image…
BTW…these are not EF grade coins…maybe VG to Fine… That’s
old coin coin grade, which varies a tad from normal numismatic std
for modern stuff…and it gets argued about…
I get the coins to make jewelry out of…
Ran across this ammonia rec at some site somewheres…ammonia will
not damage a silver (relatively) coin…in a soak…
And got an AlexIII (aka The Great) drachm for a bargain. Because it
was crudded black splotches reverse…and some on the front…
Later several Shahi Jital…
JOHN BURGESS…can you tell us why this might work…?
Old silver coinage was of varying silver content… But it’s worked
on black and in one case bluish grunge crust…
Cleaning a grunged coin is a crap shoot…might be flat dead and
pitted underneath… I’ve been lucky (?) four times…
Now…this is not collector stuff…$80 or under…one was so ugly,
it was under $10/…
I have also let said dealers know of my success…and the
method…
They reply…they sell them as they are, and don’t want to take
the crap shoot…
Except in extreme basket cases…but all profess ignorancs of the
ammonia soak…(?)…
JOHN…?
Gary W. Bourbonais
A.J.P. (GIA)
Gary,
Whilst I don’t want to comment on polishing new silver chain, I
would like to suggest that you take care using ammonia to clean any
valuable coins, it is an old fashioned method that we now know is not
appropriate. The problem with using ammonia is that it can cause
embrittlement of the metal and lead, over a period of time, to the
metal literally turning to dust. I frequently come across this
problem in old clocks where, for many years, the standard
professional method of cleaning them was to scrub the parts in a
solution of soft soap and ammonia, rinse in clean water and then
allow them to dry in a warm place. When I see them now, I find that
individual teeth or whole sections of wheels have fallen away and
turned to dust. The problem is twofold - partly mechanical and partly
chemical. When an ammonia solution is used it penetrates into any
cracks or gaps in the metal structure. These micro cracks are most
often found in metals which have been forged or coined where the
hammer blows have flattened the individual grains of metal into hard
plates - ordinary cast brass is less susceptible as the grains are
rounded and softer and so can absorb the stresses better. The rinsing
of the metal does not remove this ammonia from deep within the crack.
As the metal dries, the ammonia is concentrated and drawn into the
furthest recesses of the cracks by capillary action until it forms a
compact anhydrous plug at the bottom of the crack. Now, the next time
the metal gets wet or the atmospheric humidity changes, this
anhydrous material swells as it takes in the water and exerts a very
strong force on the metal grains. Over a period of time this
continual prising action loosens the grains and they simply fall
away. This is the primarily physical action. The chemical action is
known as Hydrogen embrittlement where the atoms of the Hydrogen in
the Ammonia (NH_3 or, in its Hydrate form HOH-NH_3 ) diffuse into the
brass and chemically change the atoms of the copper and the Zinc to
form a copper-Hydrogen complex (either CuH_1 or CuH_2 ) which in turn
releases electrons which attach to the Zinc and effectively corrode
it. I’m sure John Burgess can correct any of the chemistry here and
improve on my description - its a long time since I did high school
chemistry!! Anyway, the point is that, whilst using Ammonia solution
to clean copper or silver (a silver / copper alloy) coins may produce
a good finish in the short term, it could easily cause damage in the
long term which would destroy the coin. Remember, these items are
only on loan to us to hold in trust for the next and future
generations. A better system of cleaning the coins would be to set up
a simple ‘reverse plating’ bath - also known as an ‘ionic cleaner’
which have been described on this list before. I made the one I use
very simply from a small glass jar with straight sides, a piece of
stainless steel shim salvaged out of an old computer disk drive and a
’wall wart’ low voltage mains adaptor which supplies 6 or 9 volts DC.
This is the system widely employed by museums for cleaning off metal
articles salvaged from the seabed or for other archaeological metal
artefacts which are too delicate to clean by physical abrasion.
Best wishes, Ian
Ian W. Wright
SHEFFIELD UK