If you ask ten United States gold coin experts what the most important pedigrees are, you are certain to have the Bass collection mentioned nearly every time. Clearly, the Bass collection was among the greatest collections of United States gold ever assembled. But I’ve learned a dirty little secret about some of the Bass coins that I’d like to share with you. Harry Bass was a pretty compulsive buyer and many of his coins came from the major auctions of the 1960’s and 1970’s. When these coins were shipped to Harry, they were enclosed in the clear plastic "flips" that were popular during this era. What we now know is that these flips were made with polyvinylchloride (or PVC) which is an oil-based chemical that imparts a residue on coins.
I don’t know this for a fact but I believe that many of the Bass coins were stored in PVC flips for many years; in some cases as long as two or even three decades. During this period, a lot of PVC "grime" got onto the surfaces of the Bass coins.
So how can you tell if a Bass coin has PVC grime on it? Generally, gold coins with this residue develop a sort of cloudy whitish film that seems to become thicker with the passing of time.
The coins that appear to have the most noticeable residue are in PCGS holders and have "original" Bass pedigrees. If a Bass coin was removed from its original holder but resubmitted later to PCGS (in an attempt to upgrade it) it was still given a Bass pedigree but to distinguish it, it was designated as "Bass" on the insert by PCGS. Coins that are in their original "first generation" Bass holder have a pedigree on the insert that states "Harry W. Bass Collection." There are also NGC coins that have Bass pedigrees. These were in the Bass collection but were cracked out of their original holders. Ironically, I have never seen an NGC Bass gold coin with any PVC grime on its surfaces.
How serious of a problem is this PVC? I am not a chemist and would defer the chemistry-related issues inherent to this question to someone else. From what I do know about gold, it is a very inert metal and one that is far more forgiving than, say, silver or copper. If the Bass collection had been copper coins and they had been stored in PVC flips for years, I think the coins would have been at considerable risk. Being gold coins, I think they were at far less risk. I’m not certain if the residue from these plastic flips did any long term damage but in the instances that I have seen coins on which the residue was removed, the underlying surfaces seemed just fine.
For me, the biggest problem with these coins is aesthetics. Some of the Bass coins in their original holders that I have seen with this PVC grime simply aren’t very attractive. If you purchased coins from the Bass sales in 1999-2000 and you haven’t inspected them recently, I’d suggest you take a quick peek and see how they look.