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Black Gunk..

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Bedrock of the Community
10726 Posts
 Posted 12/19/2009  07:03 am Show Profile   Bookmark this topic Add SHAFTA9a to your friends list Get a Link to this Message
I picked up a 1866 Indian cent a while back, I know this has been answered before, but this coin has a bunch of black gunk on it, I have had it in Olive Oil for a couple days, seemed to help it a bit, but was there something else that would take it off better?

Thanks for your responses.
True North
Valued Member
United States
199 Posts
 Posted 12/19/2009  10:44 am  Show Profile   Bookmark this reply Add Brewzz to your friends list Get a Link to this Reply
Have you tried a soak in Acetone?That might help,depending on what the gunk is made up of....
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United States
23521 Posts
 Posted 12/19/2009  10:56 am  Show Profile   Bookmark this reply Add SsuperDdave to your friends list Get a Link to this Reply

I have had it in Olive Oil for a couple days, seemed to help it a bit,

I've been working on an Indian head. It's been in olive oil since December 2007. Not done yet.
Valued Member
United States
123 Posts
 Posted 12/19/2009  11:48 am  Show Profile   Bookmark this reply Add freewheel to your friends list Get a Link to this Reply
I have soaked coins in acetone but have not heard of olive oil. How does this help? and why soak them so long?



Pillar of the Community
United States
1883 Posts
 Posted 12/19/2009  2:53 pm  Show Profile   Bookmark this reply Add ratman4762 to your friends list Get a Link to this Reply
Soaking coins in olive oil removes encrustation. It is a method widely used on dug ancient Roman coins. It has no ill effect on the coin. The downside is that it takes a lengthy soaking or several soaks with a removal of loosened encrustation between soaks.
Bedrock of the Community
United States
19337 Posts
 Posted 12/19/2009  5:15 pm  Show Profile   Bookmark this reply Add just carl to your friends list Get a Link to this Reply
Hope you end up with more luck than I've been able to do with dark spotings on Indian cents. I've tried the Olive Oils, Vinegars, Acetone, Baking soda and distilled water, Laquer Thinner, Mineral Spirts and lot of other solutions and so far nothing good to report.

Note in the attached photo the Indian cent. When I first started with these coins that one had that dark stuff on it and still does. All of these coins were either polished, cleaned, corroded, etc so nothing to loose experimenting. All were in the same solutions at the same time and all are now on a kitchen window sill. The Indian cent only turned a reddish color but the dark stuff stayed there.
just carl
Pillar of the Community
United States
1729 Posts
 Posted 12/19/2009  8:09 pm  Show Profile   Bookmark this reply Add pls to your friends list Get a Link to this Reply
I use Goo-Gone for non-critical coins. Works like a charm, but I have no clue as to any residual effects. Takes black goo off immediately - probably chewing gum or road tar.
Bedrock of the Community
United States
16494 Posts
 Posted 12/20/2009  11:34 pm  Show Profile   Check BadThad's eBay Listings Bookmark this reply Add BadThad to your friends list Get a Link to this Reply
Whenever you have residue and want to try to conserve a coin, you should follow the solvent polarity ladder. Randomly trying different solvents is not systematic, it is problematic. You'll never figure out exactly what kind of residue you have and whether or not you'll be able to remove it by darting around. The goal is conservation and if you're not careful you'll cross-over into the evil world of cleaning.

Here's an except from my upcoming book on verdigris....but it applies here too. I also have an in-depth look at olive oil that should make for interesting reading.


ALWAYS be aware that sometimes organic residues can be green and mistaken for verdigris. Just because a coin surface contaminate is green doesn't necessarily mean it is verdigris. Coins can be exposed to anything and everything during their existence. That green spot could be a very old piece of gum. For this reason it is recommended to first try what I call the solvent POLARITY LADDER shown below:

Wannabe Geek Note: Polar means a chemical has a negative charge on one end and a positive charge on the other end.

Very Important Note: Only use glass containers with a tight fitting lid for soaking coins.

TABLE 3: The coin solvent Polarity Ladder.

Deionized or Distilled Water Polar
Acetone Less polar than water
Xylene or Hexane Non-polar


Water will remove many polar surface contaminants. On the Polarity Ladder we start with the absolutely safest coin solvent in the world. As long as soak times are kept reasonable, probably less than 7 days, distilled water will not damage a copper coin. When water soaking, be sure to change out the water at frequent intervals. The more frequent the water changes, the better. Remember, the water is dissolving unwanted contaminants so it becomes contaminated. Each time you change it you're throwing away the bad stuff. Always use distilled or deionized water for soaking. Unpurified water or tap water contains contaminants that may deposit on the coin defeating the conservation attempt.


Acetone chemically, OC(CH3)2 , is a very polar, organic, volatile solvent. High grade acetone can be purchased at most hardware stores. It can also be ordered over the internet in a higher grade like ACS (American Chemical Society) but at a much higher cost. It will remove many organic materials from the coin surface.

Warnings: Do not soak in directly sunlight and store your acetone away from sun. UV light can degrade acetone and produce some chemicals that might be hazardous to your coin. Never allow the acetone to evaporate while the coin is soaking or everything that was dissolved will simply be redeposited on the surface. Use high quality acetone only! DO NOT USE NAIL POLISH REMOVER! Acetone will dissolve plastics and styrofoam so only use a glass container with a tight sealing lid when soaking in acetone. Acetone is flammable; keep open flames away from it. Be sure to read the label and MSDS so you understand the hazards of working with this organic solvent.

A good test to perform before using acetone on a coin is to place some in a glass dish and allow it to evaporate. Inspect the bottom of the dish once it's gone and make sure there's no residue, haziness or sticky film. Any acetone that fails this test is impure and should not be used on a coin.


Xylene is what we call a non-polar solvent and it's completely safe on copper. It's important to use a non-polar solvent because it's the only thing that will dissolve some organic residue. If the surface debris is non-polar, chances are that xylene will be able to dissolve it. Remember "like dissolves like"! Do not over-soak in xylene or you may affect the patina, it can lighten a brown patina with enough time.

That is the process of stepping through various coin safe solvents before attempting conservation. If the green is removed, then it was most likely organic (carbon containing) in nature.
Lincoln Cent Lover!
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