Mario writes: I have several Morgans, MS 63-67, in plastic folders and have them in a safe. Should these coins be placed in PCGS holders to protect them from moisture and mold? Also, is there something I should keep in the safe, moisture wise, to protect the coins. I have paperwork in the safe also and often open up the safe to level out the atmosphere. Thanks for any help.
First of all: Don’t keep coins in polyvinyl flips. They eventually decay and release an oily film that will damage most silver, nickel and copper coins. Small amounts of hydrogen sulfide are released at the same time which is corrosive. It can take as 6 months or longer for the spots to appear after contamination. The presence of any polyvinylchloride holders in a closed area can also be a source of damage. PVC decays over time releasing corrosive hydrogen sulfide gas and a oily softener. Coins stored inside PVC will be severely damaged by these products. Silver coins usually turn green and lose their luster. Paper money will also be affected by PVC, mold and moisture.
Use only inert materials such as Mylar, acetate or hard plastic to store coins for long periods of time. PCGS or NGC holders are not dangerous but do allow air to enter. Cardboard coin boxes are OK. Though they contain sulfur, they won’t affect coins not physically in contact with the box. If humidity is a problem in your area, you can purchase a product that will absorb moisture and pollutants from the air. See: Intercept Shield
With all the noise about storage mediums, it seems that the old standard cardboard 2x2s with the acetate windows are fine for coin storage. I have mint state U.S. cents from the 20’s and 30’s that are still full red that have been stored in 2×2’s in a cardboard coin box for many years. Modern U.S. Mint sets usually store well in their original packaging as long as they are not in contact or near decaying PVC.