To clean or not to clean this Bombay Presidency milled rupee?

[cmerc]

It is well agreed upon that the decision to clean a coin and the cleaning technique depends on the coin in question.  So here's the coin in question: Bombay Presidency milled rupee, 1215-46, Pridmore #284.  I think it is a nice F-VF, but the black toning/dirt detracts it from its potential eye appeal. 

• Should I clean the coin? I don't want to risk damaging it.
• If yes, what would be best way to get rid of the black stuff?

Given the relative scarcity of this coin type and my limited budget, I am satisfied with this coin.  Wouldn't mind making it look a nicer though. 

[malj1]

Soap and warm water and perhaps a soft brush will suffice, dab dry with a soft cloth.

[cj_fam]

Never clean your coins, definitely not with soap and brush, this will significantly degrade the value of the coin. If you really want to get the stuff off, try dipping it in a mild cleaning solution and rinse under running water, do not rub the coin.

[akona20]

Cleaning by the advised method will not substantially degrade the value (if at all) if done carefully.

The coin not need or require cleaning to present maximum value at sale in the real marketplace.

[Coinsforever]

If I'm not wrong it seems some grease or oil marks on the coins surface .

Warm water with mild soap solution will remove a bit greasy content ,  but rubbing & brushing will definitely ruin the surface  due to scratches /marks.

Cheers

[Figleaf]

Never clean your coins, definitely not with soap and brush, this will significantly degrade the value of the coin. If you really want to get the stuff off, try dipping it in a mild cleaning solution and rinse under running water, do not rub the coin.

This sort of advice fits a very narrow category of coins (sort of), but is not appropriate for most coins. Cleaning will not significantly degrade the coin, unless it is done badly and ignorantly. Water and soap cannot attack metal, while it solves fatty substances on the coin (including fresh fingerprints), but not drying the coin properly may cause damage. There is an extensive discussion on the cleaning board and in other threads, showing plenty of coins that couldn't even be read without cleaning.

On this coin, it depends on what the "black stuff" is. If it is dust and mud, water and soap will suffice - it may take a bit of a soak. If you are still unhappy afterwards a soft eraser wil help.

Peter

[akona20]

The question about this coin is what is the percentage of silver in the coin? Given the source the percentage can be researched. Given the percentage the "tarnish" effect is probably natural.

[cmerc]

Thanks for all the suggestions.  An update on what I did based on your inputs. 

Soaked in in acetone for an hour.  No effect on coin.  Black parts are either toning (Ag20?) or stubborn dirt.

Soaked in in hydrogen peroxide solution to get rid of stubborn dirt.  The darkest portions of the coin bubbled vigorously, indicating that it is probably stubborn dirt.  Kept monitoring it every 30 seconds.  However, before the dark black regions went away, a rainbow tone (oxidation layer??) developed on the exposed silver bits, particularly the reverse.  Not very attractive.

Will try buying some ammonia and soak the coin in ammonia solution tomorrow.  IMO, the coin has enough detail/relief to look good when clean.  Just want to get rid of the black patina: not very attractive. 

As advised, did not run the coin with anything abrasive.  Just tried lightly rubbing my finger across a few times with acetone, to check if dirt is easily removed (not easily removed ).  There is definitely some dirt on it. 

Coin status as of end of tonight:

[Coinsforever]

Coin status as of end of tonight:

Congrats , Smart looks after short makeover


Cheers

[akona20]

SIGH!!!

[cmerc]

SIGH!!!

!!  I generally do not clean coins at all, except for a soak in acetone.  This one looked like a good candidate to try.  I understand your frustration/disappointment, but one has to experiment to learn.

Let's see what ammonia does.  I think I have spent enough time researching the chemistry.  The black stuff is silver oxide, which reacts/dissolves in ammonia.  Good.  However, the alloy contains copper, which turns into blue compounds with ammonia.  Bad.  A short exposure to ammonia should remove most of the black, but prevent too much blue.  Fingers crossed. 

[akona20]

Before you even think of experimenting you must understand the composition of the coin.

So what is the silver content of this coin?
What is the NORMAL effect on such silver in what can be termed in numismatic terms toning?

There have been a number of debates here recently on cleaning and toning in which misinformation seems to have been part of the process.

So before you clean you must understand nowmal process.

But hey if you want a coin that shows "as struck" it is no more than a manipulation of process.

[cmerc]

Did some research about the coin and chemistry.  This coin is ~92% silver, and 8% alloy.  It originally had a lot of dirt on it, along with black toning.  The only silver compound that appears black is silver oxide (Ag2O), hence the toning is likely to be silver oxide.  The dirt also appears black.

Got some ammonia (i.e. 10% ammonium hydroxide solution) today from the hardware store.  Silver oxide, reacts in excess of aqueous ammonia solution to form a soluble compound.

Ag2O(s) + 4 NH3 + H2O <---> 2 [Ag(NH3)2]+ + 2 OH-

So the black toning should disappear if left in the ammonium hydroxide solution I got.  I diluted down the solution considerably to start with a milder condition.  Kept checking my coin every 30 seconds or so, and stopped the process after 5 mins.  Rinsed the coin thoroughly in running water and then soaked for a long time in acetone to get rid of any ammonia.  Below are the before and after pics.

As you can see, there is still considerable black spots and some dirt remaining (around the 'julus' word).  But given the initial state of this coin, and the price I paid for it, I am happy.

Moral of the experiment:  (1) I will never use ammonia on coins again.  Too strong and dangerous.  And I will not clean coins again.   (2) I will not buy coins that I do not like, and will patiently wait for better specimens.

FIRST PICTURE: Coin photographed by dealer.
SECOND PICTURE: Before cleaning (except acetone soak), photographed by me.  (Rescaled from pic above.)
THIRD PICTURE: After cleaning using aqueous ammonia.

[akona20]

The Bombay series of EIC type coins has been tested for meatl content. This coin is aproximately Sterling Silver. As a natural process Sterling Silver tarnishes. Coins that are Sterling Silver of this age that have not oxdised have been cleaned.

So is it acceptable to clean these coins? Well not if you are true to the cause of arguing about bright shiney coins and anti cleaning. But there will be continued discussed about how great some bright shiney coins look and other arguments about cleaning marks on coins being bad. lol. So what is being hawked around is that if you can clean a coin without marking it that is okay but it is bad if you mark it. Hmm.

[cmerc]

The Bombay series of EIC type coins has been tested for meatl content. This coin is aproximately Sterling Silver. As a natural process Sterling Silver tarnishes. Coins that are Sterling Silver of this age that have not oxdised have been cleaned.

So is it acceptable to clean these coins? Well not if you are true to the cause of arguing about bright shiney coins and anti cleaning. But there will be continued discussed about how great some bright shiney coins look and other arguments about cleaning marks on coins being bad. lol. So what is being hawked around is that if you can clean a coin without marking it that is okay but it is bad if you mark it. Hmm.

In general, I am against cleaning except for a short bath in acetone  to rinse away oils and fingerprints.  On this coin, most of the black stuff was not natural tarnish (Ag2O), but dirt.  In fact, there was some green/yellowish plastic/rubber spot on the obv at 3 o'clock.  I used non-abrasive ways to get rid of the dirt.  Some of the dirt along with the tarnish still remains and I shall leave it be.  The goal was to reveal more details without damaging the coin.  I got lucky with this coin, but will not do it again.