Slabbed gold coin vacuum seal experiment... now what to do?
Paul1967
Posts: 11
I started a couple of Gold American Eagle $5 coin collections a few years ago. I wasn't sure of the best way to store the coins being a reborn newbie. ( That is to say, I collected circulated coins from spare change as a kid but now I can actually afford to BUY my coins. 
)
I decided to try an experiment. I stored both PCGS and NCG slabbed Gold American Eagles in my fire proof safe with ample, monitored silica gel. Some slabs were also vacuum sealed in Foodsaver bags (which are made of polyethylene with an outer layer of nylon, not PVC). I figured the downside for this collection was small since bullion value accounted for most of the purchase price.
Results after two years: The vacuum sealed coins look the same as when I stored them. Those not vacuum sealed have aged with mixed results. Most have started getting a darker gold tone but are not ugly. One NGC slabbed coin has ugly spots on the reverse -- I think it must have been slabbed with something on it in the first place. A few of the slabbed GAEs not vacuum sealed have aged with uneven toning that is not attractive.
Questions:
1. What were the likely contaminants? A fire proof safe has a coating that releases a gas when hot -- is that an issue? I had some zip lock bags with birth certificates and a cardboard box, too. Everything else in the safe was either a polyethylene or a polypropylene container.
2. What do I do with the uglier toned coins, especially the ugly spotted one? Some of the coins have increased in price nicely in two years, beyond the increase in spot price, so I don't really want to mess with them, but others are still trading at close to spot, and fortunately gold is significantly up from when I first started this experiment. I am templated to crack and dip the common dates and sell them as bullion on ebay. (I suppose I should expect a flame for even thinking this.) My goal is to simply have attractive sets and unload those coins that don't fit with the rest. What to do?
I am now sold on the idea of vacuum sealing slabs for storage, accepting the downside that one side of the coin will be hard to see due to the bag mesh that creates an air channel. I suppose I like what I read about Intercept and someday I will release these coins from their vacuum bags in favor of Intercept 10 boxes.
Thanks for considering my questions.
)I decided to try an experiment. I stored both PCGS and NCG slabbed Gold American Eagles in my fire proof safe with ample, monitored silica gel. Some slabs were also vacuum sealed in Foodsaver bags (which are made of polyethylene with an outer layer of nylon, not PVC). I figured the downside for this collection was small since bullion value accounted for most of the purchase price.
Results after two years: The vacuum sealed coins look the same as when I stored them. Those not vacuum sealed have aged with mixed results. Most have started getting a darker gold tone but are not ugly. One NGC slabbed coin has ugly spots on the reverse -- I think it must have been slabbed with something on it in the first place. A few of the slabbed GAEs not vacuum sealed have aged with uneven toning that is not attractive.
Questions:
1. What were the likely contaminants? A fire proof safe has a coating that releases a gas when hot -- is that an issue? I had some zip lock bags with birth certificates and a cardboard box, too. Everything else in the safe was either a polyethylene or a polypropylene container.
2. What do I do with the uglier toned coins, especially the ugly spotted one? Some of the coins have increased in price nicely in two years, beyond the increase in spot price, so I don't really want to mess with them, but others are still trading at close to spot, and fortunately gold is significantly up from when I first started this experiment. I am templated to crack and dip the common dates and sell them as bullion on ebay. (I suppose I should expect a flame for even thinking this.) My goal is to simply have attractive sets and unload those coins that don't fit with the rest. What to do?
I am now sold on the idea of vacuum sealing slabs for storage, accepting the downside that one side of the coin will be hard to see due to the bag mesh that creates an air channel. I suppose I like what I read about Intercept and someday I will release these coins from their vacuum bags in favor of Intercept 10 boxes.
Thanks for considering my questions.
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Comments
I vacuum sealed four PCGS MS69. Left 4 others (PCGS MS69) 'open'.
After 2 years the 4 open ones darkened slightly, the 4 sealed ones didn't change at all.
so it seems like if you slad a coin that is basically inert in a good quality archival holder the key is to get an airtight seal around it
i wanted to ask do the new ngc holders are they airtight with argon gas introduced into them at the time of slabbing as i have heard???
After posting I read up on cleaning coins for, oh, maybe the 10th time in my life. Every quality set of guidelines goes about the same...
1) Don't do it -- you'll probably ruin it, dummy!
2) If you are having any doubts at this point, see rule #1.
3) If you're still reading, proceed at your own risk and expect to wind up with a slug.
Regarding NGC versus PCGS slabs, my little experiment showed less toning with NGC slabs than with PCGS slabs. However, the ugliest spotter of the bunch is a 1999 GAE $5 MS69 in an NGC slab. But the way it looks I would have to think that something was on the coin when it was slabbed. This wasn't a test done with controlled conditions and a significant sample. I have 6 toned GAEs that were not vacuum sealed, 5 in PCGS slabs, with 2 PCGS and 1 NGC that are no longer attractive in my opinion. 8 slabs left out of vacuum sealing packaging did just fine. Also, two years is the average timespan. I didn't start this experiment on the same day for all coins. What I can say for sure is that vacuum sealing my slabs kept my gold coins as bright as the day I received them. I'd rather burn through Foodsaver bags whenever I want to gaze at a coin preserved in this way than discover spots or toning in the future.
But really,anytime you can create an inert environment,it couldnt hurt.