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Author Topic: Understanding what horn silver is  (Read 1250 times)

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Offline Basileus Nikephoros Antialcidas

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Understanding what horn silver is
« on: March 10, 2020, 09:53:47 pm »
Hello. I would like to ask if anyome can help me understand horn silver. Is it like bronze disease? If ila coin has some will it spread slowly and eventually destroy the coin, or it is going to stay were it is without further damaging the coin. Also what makes horn silver form? Can someone understand from a photo of a coin if the coin has horn silver or just patina? Thank you all for your help!
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Offline v-drome

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Re: Understanding what horn silver is
« Reply #1 on: March 10, 2020, 10:23:15 pm »
Horn silver is silver chloride, AgCl, and usually forms on silver coins in the presence of salt water or in wet ground near an ocean.  It is very destructive, but I don't think it keeps eating at the coin after it is stable.  If it is anything more than a very light layer, removing the horn silver with an acid or other chemical often takes much of the coin's detail with it, and would harm the coin.  Others my have more information on this topic.

Offline shanxi

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Re: Understanding what horn silver is
« Reply #2 on: March 11, 2020, 07:55:54 am »
In fact, what we call hornsilver is a wild mixture.

AgCl (silver chloride) the pure "horn silver" is a white, highly light sensitive substance.

When exposed to light it slowly decomposes to elemental silver or frequently changes into black silver sulfide.

The color then changes from white to brown to  black. It can even take on a silver appearance.

What we call hornsilver is a mixture of all these components.

AgCl is soluble in Ammonia or Thiosulafte, but after turning into Silversulfide (Ag2S) it is not longer soluble in any common solvent.


Offline djmacdo

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Re: What is horn silver?
« Reply #3 on: March 11, 2020, 11:44:41 am »
Horn silver is a corrosion product, silver sulfide if I remember correctly.  Unlike bronze disease, horn silver does not spread but is quite stable.  One warning--do not ever try to clean thick horn silver with the old lemon juice and aluminum foil trick--that only turns the surface level back to metallic silver and leaves it coating the underlying horn silver and makes it impossible to clean further.  Innumerable coins have been ruined that way. 

Offline SC

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Re: Understanding what horn silver is
« Reply #4 on: March 11, 2020, 07:43:02 pm »
And I thought it was just the very hard black layer....  Learn something new every day.

Here is an interesting related article: "Degredation of archaeological horn silver artifacts in burial."

https://link.springer.com/article/10.1186/2050-7445-2-5

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Offline JBF

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Re: What is horn silver?
« Reply #5 on: March 11, 2020, 10:33:24 pm »
Why is it called "horn silver"?  I mean "silver" seems obvious, but what does "horn" indicate?  When and where did it get that name?

Not that it matters in the grand scheme of things, more a matter of curiosity like the grand debate of whether to say pat-i-na or pa-ti-na.  (It is a matter of what em-Pha-sis on which syl-LA-ble ;) ).

Offline shanxi

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Re: What is horn silver?
« Reply #6 on: March 12, 2020, 07:41:21 am »
Why is it called "horn silver"? 


It's called hornsilver because the hornsilver mineral, Chlorargyrite, looks somehow like the horn material of animals.

Offline Joe Sermarini

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Re: Understanding what horn silver is
« Reply #7 on: March 12, 2020, 02:36:42 pm »
I merged the duplicate threads and moved them here to the conservation board.
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