Cleaning Silver - Plasma Cleaning legit?

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Steam works great to clean the surface of a coin, but as said, will not remove the toning. It also heats the surface of the coin up, which makes the metal more reactive to possible oxidation until it cools down to room temperature.

 

True, but even so, if you take two separate pieces of like metal and push them together, they will not bond to each other in quite the same way they would if the pieces were melted together and reformed as one. That is, unless tremendous force and/or heat were used. And such force or heat would severely deform a coin.

Even the original striking of a coin will not bond together laminated layers in the metal. If it did, we wouldn't see so many "delamination" planchet errors.

 

I always thought laminations were caused by impurities in the planchets left over from the original smelting of the metal. The impurities would have a different composition than the metallic planchet, so I would not expect them to cleanly bond to the metal during striking.

 

Oxidation only occurs on the surface. If it takes an electron microscope to see any possible pitting, I don't think anyone would notice.

 

This thread = it hurts my brain!


Thanks,
Jacob

 

Yes, peeling delaminations often have contaminants underneath them and that is the reason they were not bonded to the rest of it and delaminated in the first place.

But imagine a sliver of clean pure silver that falls on a larger sheet of silver going through a rolling mill. Now that sliver of silver is loosely embedded in the silver sheet. When a planchet is punched from that sheet and then struck, the sliver is still there struck into the coin. Over time with handling and/or thermal expansion and contraction of the coin, the sliver can come loose and fall out. The striking of the coin did not in any way fuse the sliver to the rest of the coin.

 

I agree that this is a possibility but wouldn't it appear as a struck through and not a lamination?

I think we are getting a little off track from the OP and I may be getting a little pedantic. As I said earlier, it would be very interesting to see some SEM micrographs to determine if the removal of oxides and sulfides by this method causes changes in the microstructure of the as pressed surface. Until we see them, we are just offering up unsubstantiated opinions (but my unsubstantiated opinion is that it will mess with the microstructure and affect the microscopic flow lines )

 

What I’m wondering is if this technique could be used more precisely than dipping too like to remove a stain or a spot from the surface of a coin or other object without altering the surroundings areas. If so could be very useful in conservation especially with verdigris spots in copper or dark stains on coins like rubber band marks etc

 

I think people talking definitively about what it can’t do are hanging their metaphorical tushies over the edge. I dispute that visible loss of luster happens at anything close to the the molecular or atomic level; it’s far more macro than that. A whole bunch of the damage that comes from overdipping comes from the activity of the specific acid used in commercial dips, and that is far more macro than the molecular scale. Let’s wait to see what the technology does.

 

My knee-jerk response is "no" -- it's a gas jet, and I can't imagine it would be easy to focus onto a small area. But I've got really low confidence on that. Maybe they can squirt it out of a needle, and maybe it recombines so quickly that the effect can be highly localized.

Guys, if you talk me into hacking together something to try this, you're going to get me in so much trouble. It's been several decades since my last "unplanned indoor lab-related prompt temperature/pressure excursion", and I'd promised myself -- and, implicitly, my insurance company! -- that I was out of that line of experimentation...

 

Mainebill, asked: "What I’m wondering is if this technique could be used more precisely than dipping too like to remove a stain or a spot from the surface of a coin or other object without altering the surroundings areas."

I've learned that a few numismatic conservators already know all about "spot conservation." Apparently, it has been used for decades and does not involve steam.

 

I know there’s people that can do this. Was just mostly wondering if lt would perhaps be a less invasive or less obvious way of doing it.