Friday, September 4, 2009

Care For Your Cash

Collectors want to know, "How can I clean cash coins that are heavily crusted with patina?" There is no simple, direct answer to this question. Well, in a sense there is, but it ignores some very important considerations. The simple answer is, "Acid bath, base bath, brush and oil." The important considerations begin with another question, "Why clean the coins at all?"

Back in 1991 I wrote an article which was published in the Numismatics International Bulletin, entitled Care For Your Cash. I am starting my new blog Oriental Cash with a reprint of that article, including images in color, which could not be published back in 1991 in the black and white hardcopy format. I hope my fellow collectors and students of Oriental Cash will find this helpful.

Improper Cleaning Methods
Recently I had an unpleasant experience with a customer of mine. Some coins that he returned by mail were not the ones I had sent him, or so I thought at first.
They had been badly scraped or sanded, the scratches running every which way. A few of them were only slightly damaged, and I could tell that they were the original coins, though spoiled. I wrote to him, asking for an explanation. In his reply, he confessed that through ignorance he returned a few of the coins after sanding them. He wrote, "As I've said, I'm new to cash coins. I saw them full of green stuff [verdigris] that was covering the design of the coins, and I tried to remove it. I also sanded all the coins I did keep." Whatever else he said, it was the last statement that really bothered me. I had sent him, on approval, several very special pieces with exceptionally attractive patinas, including one with amethyst color. To think that he may have sanded that piece!

The Value of Patina
(pronounced păt′i·na, not pa·tē′na)
When I first started buying cash from suppliers in the Far East, I mentioned that I would be acid-cleaning some of the coins. From one dealer I received an emphatic warning never to use acid to clean cash, only cleanser and a brush. I could see his point, but because we in the West do not have the æsthetic sensibilities of Orientals, I have continued to use acid to clean cash—but only those that would otherwise be of no use at all.

Something that Western collectors must be taught is the value of patina. We are so accustomed to the verdigris and unattractive discoloration that sometimes mars our own classical specimens that we lack the sensitivity to color that cash collecting gratifies. Cash, due to their age and environmental factors, come in a wide spectrum of patina colors: Everything from chalky-white to soot-black tones the coins. The usual patinas are either brown or green. We are used to these, as Western coins exhibit the same colors, but there are others.

Red-brown and blue-green often occur in the same coin, with a light yellow-white clay crust in the fields, producing an "earth and sky" effect. Powdery light-blue, or green, or even salmon-pink will occasionally color the field of a cash. Bright-orange is another, usually with dark-brown rims and characters. My favorite is the scarce purple patina, which varies from light grey-lilac and powdery to rich red-violet with actual crystals forming in the recesses, called amethyst.

Do I sound like a connoisseur savoring a vintage wine? Well, there is a lot to appreciate in cash collecting that cannot be found elsewhere. Cash collecting appeals to the artistic and antiquarian instincts equally, and it sharpens them. After having said all this, I must come to the real reason for this article—the proper care of oriental square-holed cash.

Cleaning Cash—Materials and Method
If you plan to clean cash at all, there are several items you will need, most of which can be purchased at a hardware store.
1. Muriatic acid (20% solution)
2. Baking soda
3. Plastic containers with lids
4. 3M scouring pads
5. 220 grit sandpaper
6. Bar of soap (Ivory)
7. Stiff plastic-bristle brush (or tooth brush)
8. Cooking oil (olive preferred)
9. Deller's Darkener

The plastic containers should be small and can be recycled soft margarine or ricotta cheese tubs. Any cooking oil can be used, but I prefer olive.

To clean cash, you need a well-ventilated area. This is a MUST! The muriatic acid is actually hydrochloric. This acid is a gas which is in water solution, and it is constantly escaping into the atmosphere. If you get a whiff of it, you will know it! Observe the safety precautions on the product label. Set up your cash care laboratory on a back porch or a wide-open windowsill.
Don't coop yourself up in a basement or windowless washroom!

Set up two plastic tubs—one with muriatic straight from the bottle or diluted 50-50 with water, the other with a supersaturated (heavy) solution of baking soda in water. The baking soda should not be completely dissolved; you will use the undissolved crystals as a soft scrub. These are your acids and bases. Keep the containers at least a few inches (~15cm) apart. Have the lids handy. When not in use, cover the acid solution with its lid.

Get a plastic or metal utensil that can be used to lower coins into the solutions, because you don't want to use your hands any more than is necessary. Never dip your fingers into the acid. Wear plastic or rubber gloves at all times.

Before acid-cleaning, inspect your coins for surface dirt that could block the acid. Often, a coin will only be dirty and not really need acid cleaning. Soak the coins in warm, soapy water for a few minutes. Then take your stiff plastic-bristle brush and vigorously brush each coin, adding extra soap to the brush if needed. Remember, the plastic will not mar the copper surface at all, so brush as hard as necessary. Stubborn clots of clay may require removal using a sharp wooden or plastic pick. Refrain from using metal utensils to remove surface dirt. Lay the coins out on a paper towel and blot them somewhat dry. Remove any that won't need acid cleaning, and set them aside "as is."

Lower cash singly or a few at a time into the acid. The color of the acid will change from yellow to green-black as the coin is being cleaned. The acid removes most soluble patinas but does not eat away the copper. Other ingredients in the original coin may also be soluble in the acid. The Chinese have used many additives in their alloys!

After about 5 minutes, remove the coin from the acid and lower it into the soda solution in the other tub. There will be a lot of fizzing. Using rubber gloves, you can rub the coin surface with the undissolved soda crystals which act as a cleanser. This will give the coin a reddish color. To restore a dark color to the copper, dip the coin once more in the acid bath for a minute or two, then neutralize in the soda without rubbing. Remove the coin from the soda after about 10 minutes, and blot. Some collectors soak all acid-cleaned coins overnight in a weak soda solution.

Apply oil to seal the surfaces against further corrosion. Deller's Darkener is a vaseline-like grease that darkens the surface quickly. You don't need it if you let the second acid-and-base dip darken the coin.

Not all cash are presentable after acid-cleaning, which is another reason why you shouldn't acid clean unless you know you have something positive to gain. Some cash will have very pitted or porous surfaces. The 3M pad will even out the appearance of some of these. Some cash will retain surface compounds that can be removed using the 3M pad or sandpaper. Whenever you use an abrasive, always be sure your last strokes are parallel, otherwise the result will be very unattractive with random scratches running in every direction. A properly sanded and retoned cash can still be a very presentable piece. At the time of manufacture, cash from late Ming and early Qing dynasties were usually filed, leaving parallel striations, which is also why I don't think a properly sanded coin is necessarily a tragedy. Cast coinage can be expected to undergo certain metalworking methods that are to be avoided in struck coinages.
Note: Never clean your struck coinages by this method!

Cash Repair
Occasionally, you will need to repair a cash. Large cash with cracks running from hole to rim need not be strengthened in any way, but small cash with cracks sometimes break in two when handled or cleaned. Common specimens can of course be thrown away, but a scarce specimen can be glued. A quick-drying glue such as Super Glue can be used with good results.

Cash are sometimes badly bent or buckled. These can be nicely flattened in a vise. Wrap the bent coin in an insulating material (industrial blue paper towel works well) to prevent contact with the metal grips of the vise. Very rarely when flattening a buckled large cash, the coin may break. If you tighten the vise slowly, this usually will not happen.

Cash that have been mutilated can have their surfaces repaired by careful use of abrasives; then they can be retoned. There is no reason to try to repair such defects as sand holes which occurred during the casting. Also, do not attempt to heat a cash for any reason. Copper is not damaged by heating, but other additives to the alloy such as lead, zinc or mercury will be sweated out of a coin into shiny little bubbles all over the surface.

Grading Cash
Having covered the method of cleaning, I will end this article with a short discussion on grading cash. Below are listed the various grades with advice on whether to clean or not to clean.

This is truly a beauty of a coin. The rims and characters have a smooth finish without pitting. The interiors of all the characters are perfectly clear. The fields are smooth, even glistening, if Ming or later. The patina if present is thin and even with no blobs. If there is surface dirt that can be safely removed, do so, but do not acid clean!

As above, but possibly with some detracting features. Remove surface dirt if necessary, but do not acid-clean!

Some signs of wear, some blurriness in character interiors, heavier patina. Some coins of this grade can be heavily patinated. If the patina obscures the characters, you can try acid-cleaning, and the result may be an agreeable, barely porous coin that can be artificially toned brown. This is where experience begins to kick in.

An average cash with clear characters but obviously worn. There is usually a moderate to heavy patina in the fields and a thinner patina on rims and writing. Character interiors can be filled in. Heavier patinas on such coins, when removed, still present a decent specimen.
It is best not to acid-clean, as long as the writing is not obscured.

A below-average cash. Perhaps average for certain types or dynasties. Characters are visible but worn with most of the interiors blurred or filled in.
Acid-cleaning does not improve these at all.

Sometimes, to bring up the design, careful use of a 3M pad will yield good results.

1. Never acid-clean in a closed work area.
2. Never let the acid contact your skin.
3. Always neutralize acid-cleaned coins in a baking soda solution and seal them with oil.
4. Never acid-clean a coin with light or moderate patina and legible characters.
5. Never acid-clean a coin with brown (or other very light) patina.
6. Never use a metal tool or brush to remove surface dirt.
7. Never use an abrasive on a coin better than GVG grade.
8. Never heat a cash coin to tone it.


  1. Hello Norman, Just found your website. Very helpful information on cleaning cash coins. However, my problem is a bit different. I am working with a large burial lot in which large numbers of coins are stuck together with dirt and calcification and oxides. Do you have any suggestions for separating these burial coins before further efforts at individual cleaning?
    best regards,
    Dr. Allan Pacela, from California, at: