Gray spots on NGC slabs.

Skipper53

After buying strickly PCGS grades coins, I recently bought several
NGC slabbed coins. I noticed that two of the four had gray spots on
the white portion of the slab.
Is this a normal occurence ?
Could it be a contaminant that could cause problems over time ?
Should they be re-slabbed ?

Thanks

dlimb2

Skipper it may be air pockets caused by glue. I have one with the same thing and it has not bothered the coin and I have had it for a couple of years now.

Conder101

Actually it is a contaminant. When the plastic parts of the shell and insert are produced te molds are coated with a thin layer of oil called mold slip. This is done so that plastic does not stick to the molds or equipment. If the parts are not completely cleaned traces will remain on the plastic. Once the slab is assembled any place where the inner sleave touches the inside of the shell will give you that gray appearance and the defraction fringe around it cause by ligt passing through the thin layer of oil. This seems to be ver common on NGC slabs so reholdering is unlikely to help. Fortunately the oil should be harmless to the coins. (The oil that leaches out of PVC flips is actually harmless and well. It causes damage because it absorbs moisture and outgassed decompositon products from the PVC which are damaging once they are combined. And then the oil keeps them in contact with the coin. Tis is not a problem with the plastics used in the NGC slab.)

AValde

Don't clean the slab. This contaminant will add to the value of the slab when a secondary market for slab develops in 30 years. Its part of the value. Just don't clean anything. As long as it is full of gunk, the value increases.