Dry ice blasting coins?
mcmxi
Posts: 890 ✭
I was watching Modern Marvels on the discovery channel yesterday about cryogenics and there was a segment on dry ice blasting. On one of the sequences it appeared that thay used it on a coin. It was such a quick shot I couldn't be sure but I am fairly certain it was a coin. It seems like a plausible way to clean a coin. The cold shrinks anything stuck on a surface and loosens the bond. Then the CO2 expands to 800 times its size as it evaporates blasting it off. They said it wouldn't harm a surface that was harder than a fingernail. It looked like a pressure washer without the mess afterwards. Anyways I just thought I would put it out there.
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man, I sound like that moustache on MythBusters.......
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"CRYOGENIC (CO2) CLEANING SERVICE
Dry Ice (or CO2 Pellet) Blasting is one of the most effective means of removing loose surface and tightly bonded contaminants. The process itself is similar to sandblasting, but provides a non-hazardous, non-conductive, and most importantly, a non-waste generating mechanical cleaning action.
The contaminant is removed from the target item as a result of kinetic energy, thermal differentials, and gaseous expansion. Upon impact with a solid surface, the dry ice pellets sublimate to a gas allowing it to be evacuated through a high efficiency ventilation system. This leaves only the contaminant to be disposed of as waste. The process can be gentle enough to clean delicate electrical components or aggressive enough to remove bonded coatings.
... The disposal of cleaning residues such as grit (sand), glass or plastic beads, water and crushed walnut shells is becoming increasingly difficult due to stringent landfill disposal requirements and mixed/hazardous waste controls. For example, the removal of lead based paint from a one square foot area may require as much as ten pounds of sand to remove as little as two ounces of paint. This results in over ten pounds of lead contaminated waste requiring controlled disposal. ...
Some benefits and applications attributable to CO2:
Portable equipment that is self-sustained and highly efficient
No secondary waste generation
Non-hazardous, Non-conductive
Non-abrasive, and Non-toxic
Environmentally friendly
Completely dry with no moisture/residue
Cost effective"
Anybody want to call them up?
<< <i>I've used that on the cat. Works well. Never have a problem with them afterward. >>
<< <i>I looked up a couple companies that do it and there is one that you can send a test piece to for them to check out how well it works. I am considering sending them some really gunky large cents and morgans to see the results. >>
That would be interesting...if you do make sure you post the results here.
–John Adams, 1826
Ray
<< <i>I saw that episode awhile back. If I were you, i'd do a little practice on some dirty modern pieces before bringing out my draped bust pieces!
Please don't do it on moderns.
Based on the description, only a quick shot would be effective, as once the whole coin cools, you no longer have the dimensional differences between the stuff on the surface and the stuff underneath. I suspect that some stuff would come off and some stuff would not, leaving you with a unique look of cleaned looking coin specific to this process.
Why do we need another method to blast the original skin off of an old coin again? Oh, right. Gold is for messing with.
(in my best "the fly" voice)
"meeellllt mmmeeeee.... mmeeeellltt mmmeeeee..... (sprays CO2) aaaaiiiieeeeeeeee!!!"
<< <i>I looked up a couple companies that do it and there is one that you can send a test piece to for them to check out how well it works. I am considering sending them some really gunky large cents and morgans to see the results. >>
Before and after pictures, please. One of your pieces should have carbon spots on it to see if the process disturbs those as well.
Keeper of the VAM Catalog • Professional Coin Imaging • Prime Number Set • World Coins in Early America • British Trade Dollars • Variety Attribution
JP
Capped Bust Half Dollars by Variety & Die State Pictorial Refrence
Just feeling like stirring things up a bit...
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<< <i>OK. A little OT here, but why is using CO2 in such a fashion OK, but producing CO2 via driving your car bad?
Just feeling like stirring things up a bit...
you mean CO for the car
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Edit: Both CO and CO2 come out of cars, however, CO is the poison. CO2 is necessary for the circle of life. Plants need it for photosynthesis. And we need the plant to photosynthesize, because they emit oxygen
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i'd be afraid of freezer burn..
I used to use a blasting process using walnut shells and other abrasives to clean parts prior to plating. The surfaces were very clean but would never pass scrutiny within the numismatic community as anything but "altered surfaces".
In any event, I think it would be interesting to try it out.
“In matters of style, swim with the current; in matters of principle, stand like a rock." - Thomas Jefferson
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It uses ions to etch a surface.
The etch can be controlled so well that it only removes a few atoms from the surface. It can be set up to stop as the surface changes, so it can be set to stop etching as soon as the oxide layer is gone without touching the layer below.
It's a bit scary that if someone played around they could get away with removing spots and nobody could tell.
I never used it to fix a rare coin but I bet others have.
etching with ions
<< <i>If done properly, the freezing method, much like mineral oil, will not change the surface... simply allow the 'crud' to leave peacefully
Really?!
It's hard to imagine any solid which can be blasted at a coin which wouldn't cause significant damage. I'm guessing the speed must be low, then.
CO going to CO2 is an oxidation event (combustion) and, I think it does that explosively. In any event, I think the coins surface would not be harmed if it were being blasted by gaseous CO2. If it were solid CO2 doing the blasting, it would effectively ablate the coin's surface.
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<< <i>I don't think the dry ice is hard enough to damage a coin. I think the blasting effect comes from the extremely rapid expansion as it evaporates. I have held dry ice before and it wasn't very hard. But I think I will send some off and see what happens. >>
Usually the hard part is putting it down.
Dry ice blasting is similar to sand blasting, plastic bead blasting, or soda blasting where a medium is accelerated in a pressurized air stream to impact a surface to be cleaned or prepared. But that's where the similarity ends.
Instead of using hard abrasive media to grind on a surface (and damage it), dry ice blasting uses soft dry ice, accelerated at supersonic speeds, and creates mini-explosions on the surface to lift the undesirable item off the underlying substrate.
If you can send in some coins to someplace and let them test them, I would love to see before and after photos.
Not suggesting it's a good thing to strip old coins, but to me it's no different than using acetone to remove shellac from old coins.
New collectors, please educate yourself before spending money on coins; there are people who believe that using numismatic knowledge to rip the naïve is what this hobby is all about.
Wonder if this would work on Chinese fakes and ebay crooks???
<< <i>I don't think the dry ice is hard enough to damage a coin. I think the blasting effect comes from the extremely rapid expansion as it evaporates. I have held dry ice before and it wasn't very hard. But I think I will send some off and see what happens. >>
I don't think hardness of the material is the only factor. One also has to consider the force behind it. Think of a lead bullet.... the lead itself is very soft.... but look at the damage it does to hard materials. Also, think of the photos that one sees about a tornado forcing a straw through wood, etc....
I'm not familiar with the technology, but I am somewhat skeptical. If small 'pellets' are being accelerated, and impacting the coin...... even though it may instantaneously vaporize into a gas, I suspect there will be microdamage done to the coin. I suspect it will be detectable.
<< <i>
<< <i>I don't think the dry ice is hard enough to damage a coin. I think the blasting effect comes from the extremely rapid expansion as it evaporates. I have held dry ice before and it wasn't very hard. But I think I will send some off and see what happens. >>
I don't think hardness of the material is the only factor. One also has to consider the force behind it. Think of a lead bullet.... the lead itself is very soft.... but look at the damage it does to hard materials. Also, think of the photos that one sees about a tornado forcing a straw through wood, etc....
I'm not familiar with the technology, but I am somewhat skeptical. If small 'pellets' are being accelerated, and impacting the coin...... even though it may instantaneously vaporize into a gas, I suspect there will be microdamage done to the coin. I suspect it will be detectable. >>
Exactly. Even a raindrop would go through you if it were moving fast enough. They use water jets to cut steel now days.
Keeper of the VAM Catalog • Professional Coin Imaging • Prime Number Set • World Coins in Early America • British Trade Dollars • Variety Attribution
<< <i>If you put a spotted coin in a RIE chamber and do it right it comes out with no spots and no sign of anything being done to it.
It uses ions to etch a surface.
The etch can be controlled so well that it only removes a few atoms from the surface. It can be set up to stop as the surface changes, so it can be set to stop etching as soon as the oxide layer is gone without touching the layer below.
It's a bit scary that if someone played around they could get away with removing spots and nobody could tell.
I never used it to fix a rare coin but I bet others have.
etching with ions >>
Actually argon cations are good for removing milk spots from silver eagles.