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 Replies: 9 / Views: 1,204 |
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Pillar of the Community
3772 Posts |
Poll Question
We had a few topics on tetradrachms and a few on cleaning, so here one which combines the two. I have this tetradrachm which is mainly covered with a dark green patina but with the surface shining through in a few areas:   AR Tetradrachm from Emisa, Caracalla - cf.Sear(GIC)#2652 So please vote.
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Pillar of the Community
United States
513 Posts |
With the quality of metal that many of these tets have I'd be a little afraid to start cleaning it. Also it must be very low in silver to have developed a patina like that, right?
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Pillar of the Community
 3772 Posts |
No, from the weight and sound it seems to be good silver. Not really sure how the patina developed, probably from the site it was buried.
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Pillar of the Community
United States
5155 Posts |
With a composite metal like this I seriously think it would not be wise to attempt cleaning of the piece. I must admit I am a fan of an "original" crust coin. There is quite a lot to be learned from different types of patina.
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Bedrock of the Community
Australia
21788 Posts |
I think chuy1530 may be right.
The silver purity could be as low as 30%, although 50% is more likely.
With a coin of high silver purity, cleaning with a weak acid is sometimes used by the professionals, but in this case, acid may do more damage than good, due to the low (see above) silver purity.
There is too much base metal alloy that the weak acid can preferentially attack, and thus you may loose more detail on the coin than you bargained for.
Also, goodbye patina! That's OK in this case, because the patina too thick anyway.
I suspect that the legends under the patina may weak, due to a weak strike or wear. Cleaning probably won't improve the appearance of them.
I take all of my ancients to a professional (specialist ancient coin dealer) for cleaning; I don't have the nerve or judgement to do that myself. If I do decide on cleaning, it is nevertheless still at MY risk. I have lost some, I have improved some.
For safety's sake, don't clean this one, despite the upside potential. My judgement may be wrong here, but at least, you retain the coin.
Somewhat of a pity, because in the 2x2, it probably does not look to be much more than a dark brown blob from a distance.
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Moderator
 United States
23731 Posts |
I'm with the others on this one, I wouldn't try cleaning it.
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Valued Member
United Kingdom
435 Posts |
I once saw a before and after of an example of cleaning one of the low Ag tets, using careful mechanical methods to 'thin' the patina. I am not entirely sure how they managed it but the end result was a much better coin, with good but not excessive patination. So I think the answer to your question is that it depends on what level of expertise in the cleaning of ancients you have. Knowing my own limitations and thinking that this is a good coin anyway, I personally wouldn't touch it. However that is not to say that it could not be done well.
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Bedrock of the Community
Australia
21788 Posts |
The way of cleaning an ancient silver or high silver billon coin is to use a weak (dilute) acid, to slow down the speed of the reaction. Watch closely, rinsing often until you get the most pleasing result. Very thouroughly rinse when finished.
Oh yes! EXPERIENCE is essential!
And be prepared for a bad result. That's where the risk is.
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Valued Member
United Kingdom
435 Posts |
When you say a weak dilute acid, Sel, which would you choose? Lemon juice? And how much would you dilute it with distiller water? 2:1 or..? Overall and on average, how long would you expect a coin like this one to need to be submerged in this solution?
Answers to these questions would be helpful just to give me/us an idea of the process....
Thanks..
Edited by Valecrucis
11/02/2014 06:52 am
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Pillar of the Community
3772 Posts |
Quote:
Somewhat of a pity, because in the 2x2, it probably does not look to be much more than a dark brown blob from a distance. Actually no, at arm's length (and I have long arms) it look better than the scan which doesn't do the coin justice. Not intending to clean it (at least not in the foreseeable future), just wondered what posters here would say (and also wondered how many of the "never clean a coin"-gang from the MS61-69 forums would jump up and down).  |
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Replies: 9 / Views: 1,204 |
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Posted 11/01/2014 7:28 pm
