Black Gunk On 1866 Indian Head Cent

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

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THE FIRST STEPS OF CONSERVATION

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.

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


STEP 1: WATER

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.

STEP 2: ACETONE

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.




STEP 3: XYLENE

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.

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