8 hours in acetone and the PVC residue is still there...

FULL STRENGTH - don't edited around. Just to satisfy yourself, soak a silver coin in the stuff for fifteen minutes to see that it did not hurt the coin. After the soak, wash (neutralize) the coin in HOT, soapy water, and blot dry with cotton towel - better yet FILTERED compressed air. Some use hot hair dryer on high speed.

 

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thanks! I'll do it.

 

You missed water, that's the main ingredient.

2-butoxyethanol - A very good, polar organic solvent. It WILL dissolve PVC plasticizer residue. Used in millions of products but carries some pretty heavy acute and chronic health concerns.

KOH - Strong base, provides alkalinity and helps the sodium salt materials dissolve.

Na Gluconate - HLB modifier, adds detergency, cleans. Use to fill in HLB gaps with the sodium sulfonate.

Sulfonated Sodium salts - The proper name for this class of emulsifiers is "sodium sulfonates". They work by suspending oils and other lipophilic materials in solution. Will likely also act on the plasticizer residue.

I believe this product will dissolve PVC residue (2-butoxy) as well as verdigris (high pH). However, I certainly don't condone it's use. I think it's very harsh and somewhat dangerous given the 2-butoxy health concerns.

 

Thanks for all the information! Chemistry is a wonderful thing.

I once put an 8 Reales (with edge corrosion) in some hot MS-70 just to remove some of the green PVC on its surface and By God, surprise, surprise...All the green & black came off leaving me with a nice coin. If I recall it happened in several hours. I'm waiting to try that again.

 

OK, you're the chemist and I'm smart enough to listen when knowledge speaks, so my "official" position on the matter is modified going forward. Still ain't recommending it.

As a tangential question, what does chemistry say about any of these ingredients potentially turning copper - or copper oxides - bluish?

 

@SuperDave posted: "I'm smart enough [?? really ???] to listen when knowledge speaks."

Apparently not. That's too bad. Say, perhaps before you get around to publishing all your numismatic knowledge as you have posted was on your "bucket list," you'll do some experiments with MS-70 first.

 

I suspect it is due to the formation of a thin layer of copper sulfate (blue). If anyone has a copper turned blue by MS70, I could run it on our new Hitachi SU3500 SEM and do an EDXRF analysis on it. That would settle the matter once and for all.

 

I don't recommend it either but apparently it has it's place in the numismatic world. It is a good cleaner, a simplistic one, but effective. For those wishing to simply remove "mint haze" from coins, a better choice would likely be a simple sodium hydroxide (lye) solution. I have not tried this but, from a chemistry perspective, I don't see how the other ingredients would have an effect as I believe the haze is inorganic in nature.

 

http://www.translinesupply.com/PDF/MDSSHEETS/MS707530.MSDS.pdf

 

Being a edited, but I'd bet the SaranWrap you are using is either polyethylene or polypropylene...Saran is polyvinylidinechloride.

 

A word about PVC or polyvinylchloride...it is a polymer made from...vinyl chloride and is a clear, very rigid polymer. As PVC decomposes it can give off HCl (hydrogen chloride gas) which, when dissolved in water we call hydrochloric acid. As PVC is processed, to make it flexible, a plasticizer is added (a large molecule compound that gets between the polymer molecules so they can slide over one another). The most common plasticizer used to be DOP or dioctylphthalate. This is an ester. Now the plasticizer is an oily material that can ooze out of old PVC and get on coins. As the PVC decomposes, it gives off HCl which is held against the coin by the oily plasticizer residue...voila...trouble. The KOH or NaOH would destroy any DOP and incidentally would neutralize the acid.

 

I've learned more from those couple posts than I did from 2 quarters of college chemistry...

 

I pay really close attention to Kentucky and BadThad when they post.

 

Okay!

So after 24 hours in acetone, all of the green magically went away! Guess it just really needed some time.

 

I still see some schmutz on the neck, perhaps rinse in hot water.

 

That is where the metal has been acid damaged, no removing it.

 

On the subject of the discoloration that MS70 can produce on copper, I noticed this in the MSDS that Kentucky cited:

Avoid contact with aluminum, tin, zinc, and alloys containing these metals.
​

Since most copper coins have a small zinc or tin component, could that be the issue? If so, what would the reaction be?