PVC damage is caused by storing coins in soft plastic flips that contain polyvinyl chloride (PVC.) PVC most commonly manifests as a light-to-dark greenish residue, although it can appear as milky or light gray in color. It has a distinctive "plastic" odor which can range from subtle to strong. I recommend treating coins for PVC residue whenever you can smell PVC on them, even if you don't see the greenish residue yet, because if the coin has a plastic stink, the PVC breakdown process has begun.
- Put on latex gloves and eye protection. Make sure you have good ventilation, and avoid using the kitchen or any area where an open flame is present. Acetone is a powerful chemical that is extremely flammable. Although acetone doesn't burn the skin (it is a key ingredient in some nail polish removers,) you should avoid unnecessary contact.
- Pour a very small amount of acetone into the container. (Don't use plastic because acetone will melt it.) You only need about 1/4 to 1/2 ounce if you use a small drinking glass, or tiny jar. You need only enough to cover the coin by about 1/4 inch.
- Gently place the coin with PVC residue into the dish, and swirl the acetone around for about 30 seconds. If both sides of the coin are affected, turn it over and swirl the other side.
- Remove the coin and let it air dry. If the PVC residue is still present, continue with Step 5. If the coin is clean, proceed to your next coin, and when finished dispose of the acetone by pouring it into a resealable jar. Never pour acetone down a drain, or let more than a very small amount evaporate. Acetone is considered hazardous and must be handled appropriately.
- If the coin still needs further cleaning after swirling (and in my experience, most do), take a cotton swab (such as a Q-Tip) and dip it into the acetone. (Don't use cotton swabs with plastic sticks!) Then, using a firm and steady hand, roll the swab across the coin's surface on the PVC-infected areas, taking care not to use any sort of rubbing or abrasive maneuver. If the coin has a lot of PVC residue, you should replace the swab every few "rolls." Keep rolling, using new swabs as needed, until the coin appears clean, and then swirl it again to finish.
- Never rub the coin with the cotton swab. Use only rolling motions. The slightest abrasion might cause hairlines to the coin's surface.
- Sometimes PVC residue can be stubborn and will not respond to rolling. Try soaking the coin in a sealed jar of acetone for 24 hours before attempting the rolling maneuver again. If rolling still fails, try more intensive, higher-pressure "dabbing" (but don't "scrub!") If the PVC residue still doesn't respond (in other words, if the swab isn't picking up anything at all,) your coin may not be cleanable (or maybe it's not PVC residue that you see on the coin.) You could try sending it to NCS for expert conservation.
- To prevent future PVC damage, do not store your coins in soft or pliable plastic flips. Use the more inflexible Mylar flips instead. Never store your coins in any kind of plastic containers that have a smell.
What You Need:
- Full-strength acetone (sold where paint supplies are found)
- Small glass or metal dish (PVC melts plastic!)
- Coin with PVC damage
- Latex or rubber gloves
- Protective eye-wear
- Cotton swabs (such as Q-Tips)