Discussion in 'Coin Chat' started by mrbrklyn, Apr 29, 2012.
I am totally amazed by the amount of info available in the worlds greatest library, the internet!
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You might think, however, that perhaps tarnish can safely be removed in other ways. However, if any of the commercial cleaning methods demands rubbing with any kind of cloth, the answer is a loud NO for the same reason as above-even the softest cloth in the world can leave hairlines.
How about commercial solutions or "dips"? The answer is a very cautious "It depends." Inparticular, it depends on what active ingredients give the dips their effect, and these are not always listed on the label. Formerly, cyanide was one of the most popular, though among coin collectors the stuff began to lose a little of its reputation after 1916, when the illustrious J. Sanford Saltus picked up the wrong water glass while cleaning coins, and died a few seconds later, possibly without realizing that he had made a mistake. Cyanide lost the rest of its reputation a few decades later, after collectors heard that it acts by dissolving away the top layer of metal from the coins, dulling proofs with even brief use.
The dips that consist primarily of detergent mixtures may be safe for gold or nickel, but the effect on silver is likely to be an unnatural white color, and the effect on copper is an equally unnatural pale pink, which quickly retarnishes, depending on (among other things) how acid or alkaline they are, and how carelessly - if at all- they were rinsed off.
Those that derive their punch from thiourea require the same comment only more so, the color imparted to silver often being yellow or even chalky, and that imparted to copper or bronze looking like the bottom of a copper pot which has been scrubbed to remove burnt-on spills. Thiourea dips keep on working indefinitely long unless they are completely rinsed off, and they activate metal surfaces (as does cyanide), accelerating further tarnishing.
What is left? For gold or nickel proofs, get a covered dish of ammonia (either clear or cloudy will do - the cloudiness is from a detergent), put the coin in a tea strainer, dip it for a couple of seconds only, rinse immediately in hot running water, smell to make sure the last traces of ammonia are gone, air-dry; repeat only once if necessary. Whatever is unaffected by the ammonia dip will probably yield to a dip in methyl ethyl ketone (MEK).
Silver proofs may be given the MEK treatment. Ammonia is not recommended except in the emergency of black stains, against which it may not work anyway; the reason is that ammonia forms soluble complexes with the cuprous or cupric ions in the tarnished alloy, so that repeated ammonia dips leave an unnaturally white surface which-under a microscope shows thousands of minute rough streaks - irreversible damage. The stable golden and bluish tones should be left strictly alone, as they protect the coin against further atmospheric attack in the absence of grease or moisture.
We have as yet had no opportunity to test either the ultrasonic bath or the magnesium plate; these will be discussed in future editions.
There is no way for any amateur safely to remove spots or stains from copper proofs. Dulling is often associated with thin greasy films on copper or bronze; this will yield to MEK though with a certain risk of imparting a bluish color. A safer procedure is CARE, either as a dip (freshly poured only) or applied with a Q-tip and the excess removed the same way, using extreme care not to leave lint. Old CARE - even after only 5 to 10 minutes' exposure to air in a dish is not to be used, as the essential solvent has by then mostly evaporated, leaving mostly silicone, which has no effect except to retard access of atmospheric contaminants. Unfortunately, the stuff becomes sticky as it progressively dries, attracting lint.
If the above sounds a little intimidating, it is meant to; the only safe procedure for the beginner is to leave cleaning and restoration to experts. And some stains will deter even experts. The reason we do not recommend experimentation is that mistakes can be too costly even if you are not using cyanide. Beauty emphatically is skin deep on proof coins, and once it is gone, it does not come back.
The last paragraph speaks volumes
I like how he ended that paragraph:
"Beauty emphatically is skin deep on proof coins, and once it is gone, it does not come back."
On the look out for stolen Coins Thread.
Conservation should be a profitable line of serious trade based on expertise at the top of the numismatics arts and sciences.
It is, and has been been for, well, pretty much centuries.
Do you mean "to the left?" If so, it really bothers me.
What about olive oil? I've heard that works great on bronze.
He forgot Ketchup too
Making a directory of such vendors might be useful. They really need to get together and lead the way for making standards.
Human spit might not be the best solvent. Coins found in ocean wrecks can sometimes have a premium because of pedigree.
Olive oil is a mainstay in the ancient coin cleaning practice. All naturally occurring oils are long-chain fatty acids (long carbon chain with an acid group on the end). These are VERY weak acids and essentially don't attack coins. What olive oil does is to penetrate and loosen debris and the products of corrosion so they can be cleaned off. Cleaning with olive oil usually takes weeks, months or even years, the main down-side is that it often leaves the cleaned coins dark.
I thought they used a mild Sulfuric acid solution to remove the lime et al from ancients. VERY mild.
The 4 companies that pretty much everybody knows about are the TPGs - ANACS, ICG, NGC, PCGS. They will all clean your coins for you - for a price, and in some cases even do it for free. They have even been known to do it in some cases without asking you (the owner) if you wanted it done.
Beyond that, most dealers know how to do it and will do it for you for a price, or for free in some cases. And then there are a multitude of private individuals who can do it, and do, when asked. But to my knowledge none have a "company" per se. So there is no way to compile a directory of them.
As for "standards", there are none, at least none that are published. The TPGs won't tell you how they do things claiming their methods are proprietary and because doing so would, shall we say, not be conducive to business.
That said, what works and what doesn't work is widely known. In other words, more people than you can count know how to safely clean coins. And the 4 basic methods of doing so, and directions for doing so, have been posted on this forum countless times. Many of those times by me. They are -
1 - distilled water
2 - acetone
3 - xylene
4 - coin dip
That right there, that's really all there is to know.
Do you have any contacts in NCG? We would like to talk with them. Thanks
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