Why is 91% pure rubbing alcohol better than 70% & 99% for cleaning coins with PVC?
Early_Milled_Latin_America
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No pharmacies seem to have any in my area only 70% and 99%.
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What would the 99% do to the coin vs the 91%? If you put some in a glass bowl and let it be for 24 hours or 12 hours each side.
What about vinegar is that a bad idea? Trying to learn what is OK and not.
I'd use acetone.
The reason rubbing alcohol (isopropyl) is often found at 91% purity is that it forms an azeotrope with water. Greater purity requires more than simple distillation, which isn't economically feasible for a product where absolute purity isn't usually important.
I don't know about the alcohol, but vinegar is a very bad idea! Acetone is the standard go to for PVC.
And why would 70% not work?
What exactly would I have to do if I can only locate 99% what would be steps? I get that acetone is the better option just trying to understand my other options.
I used a cheap silver coin and used baking soda and hot water to clean the coin (took off all the dirt). Then rinsed it. Then 24 hours in 70% rubbing alcohol 12 hours each side (rinsed it off under water) and now the coin looks like a mirror. I used paper towels to dry the coin.
Will this method have taken off any PVC that may have been on the coin? The coin would grade authentic no matter what so if it says cleaned I don't care.
I think you're getting to wrapped around the axle. I would just stick with acetone.
Did you say baking soda?? I'm not to sure about that. Whatever you're doing, I'd like to see before and after pictures.
Disclaimer: I'm not a dealer, trader, grader, investor or professional numismatist. I'm just a hobbyist. (To protect me but mostly you! 🤣 )
PVC ... Acetone
Impacted grease ... warm mild soap and water, toothpick, warm mild soap and water, 91% Alcohol .
You might as well use 80 grit sandpaper if you are going to use compounds like baking soda, you will ruin any coin you use this method on. I know there are lots of you tube videos that say this is safe and recommend you do it, but they are wrong.
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Look on youtube cleaning silver coins with water and baking soda it removes all the dirt and make it shinny. I do not think that is for PVC but just to clean the coin. But sure does a great job and easy. You put aluminum foil in a bowl then baking soda then medium hot water then more baking soda and let it sit for 10 minutes. Then you rub the coin with the baking soda inside the bowl both sides and rinse it off then use paper towels to dry. Works wonders.
Every time I've had coins turn dark in the solvent it was when water levels were high. Perhaps it's mere superstition but I've lost a of nice Gems in high water content solution. It's happened several times. The only common denominator is high water content.
If you dump the solution every time instead of reusing it then 70% is probably OK. The problem comes when a lot of the alcohol has evaporated away leaving behind water. I use alcohol in a tightly covered bowl and then use it until it is dirty. 91% alcohol doesn't evaporate sufficiently to be a problem in this time apparently. One of the things I don't like about acetone is how quickly it disappears. I don't like such things in the air I'm breathing or worrying about an ignition source.
Acetone is fine and I use it a lot but it's more expensive more dangerous, and might be less healthful. I can get as much cleaning out of a pint and a half of alcohol as a gallon of acetone. My favorite mixture is 2/3rds alcohol, 1/3rd acetone and a splash of methyl alcohol. I always make fresh soup for my finest Gems. It doesn't seem to matter but a nice fresh mixture might bring good luck.
It is OK was just a test coin. But came out great. Much better than I ever expected actually.
Thanks appreciate the input!!!
I am guessing that with I used the 70% alcohol and baking soda before that that the PVC will not return correct? If it does then acetone time it will be. Will give it a year no rush to send it to NGC or PCGS this will be a test.
Baking soda is too abrasive if not completely dissolved and too alkaline if dissolved. Vinegar is too acidic. Both can take off a layer of metal off the surface of the coin and mute luster. The lower percent alcohols have too much water in them that make them less strong of a solvent. Alcohol, above 70% is also too flammable, that’s why they cut it to that level to reduce risk of fires when it’s in bulk form. Acetone is highly flammable, but actually less toxic than rubbing alcohol if ingested internally.
Mr_Spud
Coin looks great after baking soda are you saying it will get worse over time I see no difference at all except extremely clean. I did not but hard just softly and rinse with water after.
As said the coin came out great. I am doing the other right now same after the baking soda absolutely great and easy. Then 12 hours 70% alcohol each side with new alcohol for each side then rinse with water. So far so good.
Actually baking soda in solution (ie water and/or vinegar) bathing aluminum foil as an example will encourage a redox reaction on the coin metal surface and clean the coin with NO ABRASION - this works quite successfully.
Well, just Love coins, period.
Just be careful, easy to disrupt the surface and lose the luster with no true benefit over acetone for pvc removal. Also, the more disrupted the “skin” gets the more likely the surface will react with humidity and different corrosive agents, so until it grows a new skin more vulnerable. It’s just a good practice to use the least disruptive thing available in order to achieve the desired effect kind of thing.
Mr_Spud
just because it looks good to you doesn't mean its a good idea
altering the surface destroys numismatic value
you can take polishing compound to a coin and make it as smooth as a proof but you're still destroying it. Rubbing baking soda is altering the surface. The baking soda/aluminum/hot water trick is actually using the galvanic potential between silver and aluminum to corrode the silver, that's why whatever's on the surface falls off. I don't know if doing this briefly is altering the surface but you still need to remove the baking soda after with something. Wouldn't recommend doing this, no idea if such coins would grade straight after.
the reason 91% alcohol is better than 70% is that it takes much less time to dry so you don't risk putting a coin in a holder with water or have to leave it sitting out for many hours where dust will collect on it
acetone is still the best though be sure to test your acetone by putting some on a piece of glass on a table and leaving it to dry, you want to make sure it doesn't leave behind a film. Hardware store acetone is often contaminated with who knows what compared to lab grade acetone.
if you clean coins, the valuable ones become less valuable
alright if you are just dealing with melt values
You are polishing the coin with baking soda. As someone else said, you might as well use sand paper. That is a HORRIBLE method. Yes it cleans it, but so would a brillo pad.
Why ask if you are just going to destroy the coins?
Baking soda does MORE damage to the coin than PVC would in 1000 years. I recommend throwing out the baking soda and keeping the PVC.
Disclaimer: I'm not a dealer, trader, grader, investor or professional numismatist. I'm just a hobbyist. (To protect me but mostly you! 🤣 )
Baking-soda-and-aluminium foil removes tarnish/toning, just like silver dip. It does nothing to PVC goo. The "rubbing" part is what's frightening us; never, ever rub a coin clean, not with baking soda, not with a polishing cloth, not with anything abrasive. You will make things worse, not better. And you will definitely create a coin that is ungradable, because it will shout "cleaned" to every numismatist that looks at it.
The "dirt" you are removing isn't actually "dirt", it's a layer of silver sulfide. It's usually called "toning" if people like how it looks, and "tarnish" if they don't, but the chemical makeup is the same. Most collectors don't want the toning removed from their coins, unless it's particularly black or uneven.
We've said it before and we'll say it again: PVC goo does not "return" once the goo is removed, not unless you put the coin back in a fresh PVC album page. Bronze disease will return, if it's not treated properly, but PVC goo will not. You do not need to be paranoid about this.
As for the OP question:
As I said in another recent thread of yours, the purer the solvent, the better it will work. Diluting it with water (which is what makes up the remainder) makes the solvent less effective. So 99% is best, then 91%, then 70%. They will all "work", but the more dilute solvents will work slower. The only reason to choose 91% over 99% is cost. 91% is cheap, 99% is expensive.
A 24 hour soak in isopropanol, of any strength, is probably about 23½ hours too long. A long soak won't hurt the coin any, but won't help either. Even 70% isopropanol should do all it's going to do in half an hour; if half an hour doesn't budge the goo, then an extra 23½ hours isn't going to make any difference.
Vinegar is an acid (in its pure inedible form it's called "acetic acid"), not a solvent. A very weak, dilute acid compared to sulfuric acid (which is the main corrosive component in both silver dip and in PVC), but an acid nevertheless. It shouldn't attack .999 silver, but will attack the copper in a coin-silver or sterling silver alloy.
The problem is, your cleaning method causes a chemical reaction. In this case, it's an auto-electrolytic reaction: on the coin, silver sulfide turns into elemental silver and hydrogen sulfide gas; on the piece of aluminum, aluminium metal corrodes into aluminium oxide. This sounds good in theory: silver sulfide turns back into silver again. The trouble is, there is damage occurring to the coin at a molecular level: the atoms of silver that get "restored" by the treatment don't get put back on the coin's surface in the same place they originally resided; they get dumped randomly across the surface. Over time, this creates a pitted, chaotic, jumbled surface, compared to the original clean crystalline surface.
You can't see that molecular-level damage with your eyes, but your eyes can see their macroscopic effects: a coin becomes "less shiny", because the crystalline striation patters become blurred and indistinct as the silver atoms on the surface get rearranged by the chemical treatment.
Solvents don't cause a chemical reaction like this; they only remove the foreign matter - the "goo" - that might be stuck on the coin. It's effectively just like soap and water: the solvent surrounds the clumps of goo, lifting them off the coin's surface. The only reason we recommend using solvents on a coin instead of actual soap and water is that many soaps contain sulfur, and will cause additional toning.
An analogy: You can choose to clean your car by washing it with car shampoo (solvents) or you can choose to clean it by using an angle grinder to scrape a layer of paint off (electrolysis / acid). Yes, sometimes, the car is corroded, and you need to apply an angle grinder to it to remove dangerous rust or ugly faded paint. But if it's just dirty, then a gentle wash is all it needs and an angle grinder is way overkill.
Roman emperor Marcus Aurelius, "Meditations"
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Thanks guys this was not a expensive or rare coin just a coin worth 30$ max. I usually only buy graded coins but decided to buy a few ungraded coins. Only 1 out of 6 that I purchased I thought could have PVC so that is the one I cleaned and soaked.
If I send this coin in to NGC for grading will they still now grade it? I know it will grade authentic cleaned if they do. Is there a reason why they would just simply no longer holder it?
You took a $30 coin, sanded it down to a $15 coin and now you want to spend $35 to get it in a details holder. Maybe just post a picture of yourself setting money on fire.
I am sending a few coins to have graded it is a scarce coin it has a hole in it already that happens a lot in that area of the world (in the past people from that area of the globe did that to put their coins on strings easier to transport). I may have to wait a year or so to find a better example so for now it will do. It is a filler coin till a better one already graded comes up for sale. Once graded I have seen some sell for 150$ (in this grade) so it is worth grading.
You're the one who said it was a $30 coin. Now it's a $150 coin that you sanded down. This is an increasingly odd thread.
Ungraded you can find them for cheaper seller was asking 30$ is what I should have said but in past Heritage auctions in the same grade (graded by NGC) have sold for 150$. Many world coins ungraded can be bought for cheaper than one graded (based on what I have noticed over the years). When I said it has a 30$ value what was I suppose to say at the moment it is worth 30$ I figured why go into all the details. This topic was no created to go into the value of my coin (s).
Might as well use everclear.
Paper money eventually returns to its intrinsic value. Zero. Voltaire. Ebay coinbowlllc
What I used worked just fine for the grade the coin was in anyways.
I'd like to see the before and after before I agree with that. A coin with a little patina and a hole could well be better than a scrubbed coin with a hole.
Next time will make sure to take pics to late this round.
do they not have acetone where you live? pure acetone it is commonly used and found in hardware and paint stores. It is the established gold standard for removing pvc.
soak in clean acetone (do not smoke or have flame near by as extremely flammable). if more than soak is needed used wooden handled cotton swab to gently roll over the surfaces.
Yes but what I used did the job and I don't expect to be buying many ungraded coins moving forward just a few here and there and upgrade as I go.
I’m not a chemist but if you really want 91% could you not add two parts 70% and one part 99% and get reasonably close? Is it not the same principle of mixing gasoline octane levels?
Having fun while switching things up and focusing on a next level PCGS slabbed 1950+ type set, while still looking for great examples for the 7070.
The issue with anything but pure acetone is that you have to be concerned with what makes up the other 29%. You can go from 100% to 91% just by adding water.