Embarking on first time verdigris removal
lermish
Posts: 3,111 ✭✭✭✭✭
There are many old threads regarding verdigris removal but I had a hard time finding anything relating to verdi on silver. I won a few heavily verdigris encrusted coins in the Goldberg auction. Not a huge amount invested in case I botch it but I would like to do as a good of a job saving these coins as possible.
Here is a draft of the process I have worked out.
1. Acetone for ~24 hours
2. Fresh acetone rinse
3. Distilled Water rinse
4. Verdicare soak for ~24 hours
5. Spot verdicare application and use toothpick to break off crust as necessary
6. Maybe MS70? Maybe should use this earlier or not at all?
If there are better options or I am going down the wrong track please don't hesitate to let me know. I will of course post after pictures. Thanks as always!
Comments
interesting one!
i look forward to see where this one goes and how it turns out.
Maybe EDTA, but probably all the things you are trying will do the job. EDTA is often good if you have green salts on a coin that is toned because it chelates the green stuff but doesn’t completely strip off the sulphide toning. I haven’t used it in a very long time, but experimented with it after reading the book “Coin Chemistry” back in the day. Here’s a link to when I experimented with it and it includes info from someone else on which type of EDTA to use
https://forums.collectors.com/discussion/319353/edta-for-cleaning-coins
Mr_Spud
I might be wrong, I can't remember right now but I was always under the impression that Verdi-Care was only used for copper. I've only used it on copper cents.
I have a Walker that has some green corrosion like that - tried acetone, MS-70, and Verdicare, with virtually no effect on the green stuff. I am now soaking it in Goo Gone and the green crap is slowly dissolving away after about 3 months. Rinsed in acetone and put back in some fresh Goo Gone - might take another 6 months to get it all, but we will see. Maybe I will try some EDTA if I can get my hands on some.
Per the sales blurb:
Uh, maybe not. Just read the link to the other thread -- no clue what that stuff is or where to get it.
I went over @Mr_Spud 's post - most of it was too technical for me but it said:
I have ZERO knowledge but I read that as EDTA doesn't work with silver. But maybe the 10% copper in the coins is enough for it to work? I hope for better (and easier and quicker) results than you've had but either way will update once I have something.
INMHO, if you are not in a hurry try Olive oil for a few days first…my experiences have been excellent
I'll do that! Thank you!
You have posted excellent 'before' pictures, so it will be very interesting to see the progress and final results. I have no further recommendations beyond what is already posted. Those coins are really crusted with the verdigris. Cheers, RickO
By all means, don’t use EDTA if you don’t understand what the linked post was saying or you’ll risk doing more harm than good. But if the green stuff is from the salt in human sweat reacting with the trace copper content of a silver coin and forming copper chloride, then it might be useful because it can make the copper chloride come off the coin into water easier with less damage to the silver sulphide skin and doesn’t attack silver at all.
Here’s something I just found doing google search on “EDTA silver coin”
From https://www.jcms-journal.com/articles/10.5334/jcms.1021204/
“ Experience has shown that with coins containing 30% or more silver, there are usually little, if any, serious conservation issues, while the lower-content pieces are highly sensitive to improper handling. So, from a conservators’ viewpoint, coins can be classified into two groups:
A - silver content 30% or more
B - silver content below 30%
Hereinafter, coins used in the current experiment are marked as group A or B, according to their composition.“
“ Ethylenediaminetetraacetic acid
Ethylenediaminetetraacetic acid (EDTA, Trilon B ) is also a component of many solution formulas for cleaning silver. The solution also works effectively for removal of a thick layer of corrosion; the process is well observable and can be stopped, if necessary. In specialis§ed literature, one may still come across warnings that EDTA solution may damage the surface of the metal (Nikitin and Melnikova 2002: 172–174).
Experiment: A 10% EDTA solution was used and coins (A and B group) were held in it for up to 24 hours.
Result: The group A coin (SM10588:338) was treated in EDTA solution for 6 and 24 hours (figure 16, lower and upper half of the coin respectively). In 24 hours, corrosion products had separated from the surface of the coin but instead, a yellowish layer, that was hard to dissolve, appeared on the surface. The coin needed additional treatment with formic acid solution. The group B coin (AI7072:3) was completely cleaned just in 30 minutes without any side-effects (figure 16).
Cleaning of group A (SM10588:338) and B (AI7072:3) coins with 10% solution of EDTA. Additional treatment of coin A - formic acid solution.
Fig. 16: Cleaning of group A (SM10588:338) and B (AI7072:3) coins with 10% solution of EDTA. Additional treatment of coin A - formic acid solution.
Conclusions: Apparently, efficiency of the EDTA solution depends on the thickness and composition of corrosion products – the thinner layer on the group B coin was removed quickly while the thicker, cuprite-malachite corrosion on the group A coin needed more time. Additionally longer contact with EDTA caused yellow coloration on the coin’s surface. Hence, EDTA solution can be used for cleaning both A and B group coins, but the treatment time is limited - if corrosion products are not removed or softened enough in 2–3 hours, cleaning must be continued with another chemical agent.”
Mr_Spud
Here’s the picture that goes with the above post
Fig. 16: Cleaning of group A (SM10588:338) and B (AI7072:3) coins with 10% solution of EDTA. Additional treatment of coin A - formic acid solution.
Mr_Spud
Also, FYI - the only reason I mentioned EDTA is I thought the green stuff on your coins looked like copper chloride to me, but of course I don’t know for sure that it is copper chloride. But this is what copper chloride looks like
And here’s your coins
Mr_Spud
Good stuff, thank you! I agree, it looks very similar. I'll keep it in my back pocket and do additional research and, if I don't have reasonable success, will consider giving it a whirl.
The article linked by @Mr_Spud suggests that (for the types of coins studied - mostly copper and less silver)
formic acid is simpler to use.
However, they advise that it is wise to try other chemicals first, and then use formic acid as the final step.