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Author Topic: Removal of Sealant  (Read 2295 times)

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Offline Schatz

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Removal of Sealant
« on: September 17, 2010, 11:59:24 am »
Hi everyone,

I recently came into a batch of small Eastern Oriental bronzes which had been cleaned and waxed or oiled. Some of them show remnants or new growth of what I think is bronze disease under the sealant, and I would like to give them a couple of soda baths to stop the decay. The question for me is: Do I first need to remove the wax/oil, or will the soda do that job for me? If not, can I use acetone with bronzes as I do with silver, or would I do further harm to the coins?

Would appreciate your advice/ experience with removing oily sealants from bronze coins.
Thanks,
Schatz

Offline Daniel Stewart

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Re: Removal of Sealant
« Reply #1 on: September 18, 2010, 08:41:36 pm »
I don't think acetone or other organic solvents will harm bronze or a patina on bronze--and they will remove wax or oil, if that's what it is. If it's plastic or varothane or some such; I don't know. You could try on a small area of one coin, maybe where there's a bit of damage anyway, and see.

Offline casata137ec

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Re: Removal of Sealant
« Reply #2 on: September 19, 2010, 10:54:05 am »
If it is just wax, a boil in washing soda will do the trick as well. (I've had to do this as well in the past)

Chris
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Offline Enodia

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Re: Removal of Sealant
« Reply #3 on: September 19, 2010, 05:42:00 pm »
If it is just wax, a boil in washing soda will do the trick as well. (I've had to do this as well in the past)

Chris

wouldn't a boil in plain water do the trick just as well?

Offline casata137ec

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Re: Removal of Sealant
« Reply #4 on: September 19, 2010, 06:38:24 pm »
Probably! Just never did it... :)

Chris
Salus Populi Suprema Lex Esto - Missouri 1822

My gallery: https://www.forumancientcoins.com/gallery/index.php?cat=19691

Offline Schatz

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Re: Removal of Sealant
« Reply #5 on: September 21, 2010, 10:31:36 am »

Thanks, everybody, for your suggestions.

I did a little experimenting in the mean time, boiled the coins in plain water, boiled them in washing soda, but every time I took them out of the bowl with cold water after the boils the water still came off in little beads and pearls. I guess the sealant is some kind of commercial wax as simple mineral oil should have been dealt with by now. One of the batch has now become the sacrificial lamb and I will immerse it in acetone. In my readings I did not find anything that wold indicate an adverse chemical reaction with CU - of course, I don't know anything about the chemical proprieties of the sealant used.
I'll let you know what happens.

Generally, do you recommend sealing coppers or bronzes? I never bothered, and it never occurred to me to check all those Elymais bronzes I have for a sealant. They do not have deteriorated in their case but I do have a dehumidifier in the room they are stored in. If you buy a bronze from a rather well known dealer in that particular field do you assume automatically that they have been sealed?

Wondering,
Schatz

Offline areich

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Re: Removal of Sealant
« Reply #6 on: September 21, 2010, 02:13:48 pm »
No. Coins are not usually 'sealed' and that's a good thing in my personal opinion. A coin that never had BD will not suddenly develop it in a temperate clime and a coin with BD will not profit from 'sealing'.
Andreas Reich

Offline mwilson603

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Re: Removal of Sealant
« Reply #7 on: September 21, 2010, 03:50:24 pm »
No. Coins are not usually 'sealed' and that's a good thing in my personal opinion. A coin that never had BD will not suddenly develop it in a temperate clime and a coin with BD will not profit from 'sealing'.

I normally agree with almost everything Andreas says but in this case I disagree when he says that BD will not suddenly develop in a temperate clime.

Excerpt from e-conservation magazine online article below, (full article can be found at http://www.e-conservationline.com/content/view/863/281/)
"Copper (Cu) and cuprous chloride (CuCl) powders were used to establish the critical RH value that CuCl transforms into copper trihydroxychlorides, the corrosion products of the so-called “Bronze Disease”. XRD analysis of the tested samples showed that the rate of transformation is fast above the deliquescence point of CuCl (68.4% RH at 19.4º C) but very slow below it. The critical RH value for CuCl transformation was found to be at 63% RH. However, subtle variables such as air movement, composition of samples and type of substrate may result in the depression of the RH value that this transformation occurs. Nevertheless, the results of this study suggest that copper artefacts would be safe from the occurrence of “Bronze Disease” in the ambient museum environment (45-60% RH), provided that the upper limit is not exceeded.  (Just for reference I have included the average RH for London as in the image below.)

So I would love to be found wrong in this as I wouldn't have to keep so many Silica sachets with my coins :) but until someone can, I will continue to use Renwax to lightly seal my bronzes, and will also check them regularly for tell tale green spots.
regards
Mark

Offline areich

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Re: Removal of Sealant
« Reply #8 on: September 21, 2010, 04:11:18 pm »
That has been my experience anyway. I found out the hard way that you can easily wipe away the first signs, or better the typical colour of BD long enough to sell a coin. The oil from your hand is enough to darken it and make it less noticeable in cases where it hasn't eaten big holes into the coin yet. Most coins I had with BD already came with it and I haven't seen a new BD case in at least 2 or 3 years and rarely before that. Sure, Silica gel can't hurt as a preventive measure.
Andreas Reich

Offline Schatz

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Re: Removal of Sealant
« Reply #9 on: September 23, 2010, 09:11:33 am »

Interesting ... I only wish I had paid more attention in chemistry class but I think I was able to follow the gist of Mark's excerpt. My little experiment with acetone went well. I immersed the coin briefly (for less than a minute), then rinsed it thoroughly and let it dry under a fan. The oily substance seems to have been removed and I can pick away at the coin and give it a soda bath. Hope there won't be any surprises when I look at it again in a year.

Thanks for all the good tips and ideas,
Schatz

 

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