Why can't a slab be 100% airtight and watertight ?

Most of the gases and moisture we talk about getting into a slab is not a visible or measurable amount per day, we are talking molecular amounts. Difference in pressures can increase the flow. Rather than irritate the piranhas, just immerse a slab in a plastic food storage container with about 1 cc of black inkjet printer ink in a few ounces of water. For fun , push on the center of the slab a few times under the surface to vary the pressure. wait a few days or weeks, and look at the inside of the slab.

Obviously, do it to a slab you don't like or to one you were going to crack out for some reason.

 

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Exactly!

As Jim said, the leaking occurs on a molecular level. All plastic is porous to some extent, the plastic molecules can only pack so tightly together. Oddities in the polymerization and minor impurities in the plastic can produce bigger "holes".

The best thing to do is to store your slabs properly. I simply put mine into heavy ziplock bags with a desiccant pack and sacrificial, red cent to absorb any gases that make it into the bag. I then put the bags into a tupperware type container.

 

[/h]Why can't coins be air, water, chemical and wear resistant? That technology exists as well, but like air tight slabs, we'll never see it for obvious reasons.
Guy

 

I know that Thad and I both have stressed the "sacrificial red cent" before, but it still escapes me why someone pays extra for intercept (tm) products when they can provide similar protection for a couple of cents ( literally). I think thad puts his directly in with the coin storage, I put mine, after roughing its surface for better reactivity into a memory card holder with holes in it. I can look at it and tell if it is reacting by a change in color, and it costs a cent to replace. It may look odd, but I like it , and I drop one into each storage box or ziplock and a few in the bank box and my safe.



Jim

 

HAHAHAHA....I love that idea! I might drill out a few airtites to make a similar holder. I agree, it's a good idea to take some steelwool to the sacraficial cents to improve the surface active area.

 

That is very interesting. But I'd like to know how you know this works the way you think. I see two possibilities. Either the offending gas in the container is completely sucked into the case and absorbed by the cent (or cents) as they infiltrate the container. Or, the whole container is filled with gas and some of it that's around the cent tones it while the rest, on the other side of the container remains there anyway. It's easier for me to believe the latter than the former.

I guess I just can't believe a cent could be that powerful for a large container. I'd be interested in hearing more details.

 

The main key is the principle of diffusion. the principle that (gas) molecules are always moving ( faster at higher temperatures), and tend to statistically distribute themselves equally in a container. So imagine then a container with equal amount of sulfide ions ( probably very low unless you are burning high sulfur coal) in the container. Now as the coin reacts and removes a sulfide ions, the quantity in the container ( because they are constantly moving above absolute zero) decrease, but they keep re-distributing themselves randomly. Over a short time, most if not all will be reacted with the raw copper and stay there.Thus none left to react with the other coins.

It wont reduce any reactions that have already affected the coin, so it won't remove tarnish, but it will eliminate more.

No sucking involved.

 

pre 82 or post?

 

The post 82 cents have the pure 100% copper outer layer, so I use them

 

I would have thought a pre-1982 cent would be better. After scratching it up a bit, I'd imagine some of the zinc core might be exposed and zinc is much more reactive than copper, not sure I'd want to put exposed zinc into the mix with my nice copper coins. Plus, the cents I'd be trying to protect are the pre-1982 variety so I would think it would be best for the sacrificial cent to be of the same variety.

 

The copper layer is thicker than that. even using a small wire brush, I have never broken through the copper layer. Pure copper is more reactive than 95%. Not by much, but i see no reason to use a bronze cent. If one has a bright red 2011 cent, that would probably not even need abrading.

 

The 1965 and up clads are pretty damn wear resistant....and probably immune to air and water.

 

I am leary of the idea of placing a slabed coin in a food saver type vacuum packed bag. It is probably not a problem but the pressure could cause the slab casing to sink and rest against the coin - could it not?

 

So sulfide ions are the main threat for toning coins? The only threat? Does a cent attract anything/everything else that could be present? I'm trying to see how a cent will do an equivalent job of protecting coins as two layers of intercept shield would. You have me convinced that it can do some good and I think I'm going to take your advice and add some sacraficial cents for added protection. I don't know if I'd call it the "end all" of protection yet.

 

There is a Canadian company that vacuum seals the slabs. The owner has had a slabbed coin sitting inside a fish tank for several years now, without water penetration.

Canadian Coin Certification Service (CCCS)

Really nice, hard, clear slabs - but not overly popular with Canadian dealers, who still like the mylar flips from ICCS (International Coin Certification Service) in Toronto.

 

Well I can put at least 1 hole in the Vacuum sealing method, They would have to "seal" the slab in a vacuum chamber, not that expensive to do, however they could no longer "sonicly" bond the plastic slab (sound and vacuum don't coexist well). This is no issue if they used an inert gas... say helium, but helium can migrate through even vulcanized rubber given enough time so you would get maybe 1 year of neutral atmosphere in the slab then be right back where you started. Also you have the presure differential in a sealed slab, taken in a plane it could actualy explode (most cargo is transported unpresurized) All in all truely airtight sealing of slabs could create as many possible issues as it resolves so I don't see it happening in the near future.

 

Being a Canadian, I don't mind taking my hockey stick and slapping that horse puck right back at you!! The CCCS website does not show an example, but they definitely offer waterproof sealed hard slabs.

Some examples:

http://www.ebay.ca/itm/Canada-5-cents-1928-CCCS-MS-64-/200833882567
http://www.ebay.ca/itm/1781-North-American-token-CH-AM5A1-Breton-1013-CCCS-VF20-/251186950401
http://www.ebay.ca/itm/1920-Canada-1-cent-CCCS-Certified-MS-65-Red-Large-/380502331033
http://www.ebay.ca/itm/1952-canada-dollar-CCCS-MS-65-/380294835841
http://www.ebay.ca/itm/1964-Canada-25-cent-CCCS-Certified-PL-66-Heavy-Cameo-/110963992053