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Author Topic: Patina on cleaned coins turns from brown to green  (Read 1364 times)

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Offline DzikiZdeb

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Patina on cleaned coins turns from brown to green
« on: March 09, 2022, 01:48:26 am »
I am not very knowledgeable about patina and can't really explain how cleaning some coins changes the color of the patina from brown to green. Is the brown top layer independent of the green bottom layer and is removed during the cleaning process, or are there some chemical processes taking place that expose green copper compounds more?

Examples:

1.

Before:


https://www.acsearch.info/search.html?id=3289701

After:


https://www.acsearch.info/search.html?id=2996915

2.

Before:

https://www.acsearch.info/search.html?id=6784349

After:

https://www.acsearch.info/search.html?id=7854846

3.

Before:

https://www.acsearch.info/search.html?id=3305905

After:

https://www.acsearch.info/search.html?id=3247660

Martin R3

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Re: Patina on cleaned coins turns from brown to green
« Reply #1 on: March 09, 2022, 05:10:52 am »
Hey DzikiZdeb

I'm very new to cleaning and patina, but here are some observations to consider:

Coin 1:
While the reverse shows more detail after cleaning, the obverse does not. It seems like no material was actually removed here.
Also notice how the bronze-looking overcleaned high spots in the before image have also turned greenish in the after photo.
My best guess would be that the cleaning was aggressive (potentially involving chemicals), stripped the original patina, and the coin was re-patinaed in green afterward.

Coin 2:
This one looks like a pure cleaning job, with brown in the low spots having been removed. The color is also nearly unchanged.
The only thing that has me surprised, is that the originally smooth surface of the portrait seems to have gone rough after the "cleaning".
(That being said, I have never cleaned a silver coin / coin with intact silvering layer.)

Coin 3:
The before observe looks like rock hard encrustations. That must have been a tough cleaning job.
From the reverse the green patina is a bit surprising, but it's hard to tell.

Offline Ron C2

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Re: Patina on cleaned coins turns from brown to green
« Reply #2 on: March 09, 2022, 07:44:54 am »
In my opinion, all 3 of those was chemically stripped with acid or lye and repatinated artificially.
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Offline Lech Stępniewski

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Re: Patina on cleaned coins turns from brown to green
« Reply #3 on: March 09, 2022, 08:31:16 am »
In my opinion, all 3 of those was chemically stripped with acid or lye and repatinated artificially.

But look at the first coin. How can you make an artificial patina worn out in exactly the same places as before? Probably it could be done with time consuming manipulations but why make the job so difficult.
Lech Stępniewski
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Offline Mark Fox

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Re: Patina on cleaned coins turns from brown to green
« Reply #4 on: March 09, 2022, 03:02:54 pm »
Dear Board,

As someone who has seen a lot of coin photos over the years (including those from the auction houses in question) and who has just been doing some numismatic photography of his own, I am fairly certain the photographer(s) are at least partly responsible for the observed color changes.  The photos of the two Roman provincials (after the coins were expertly cleaned and possibly lightly smoothed), simply do not reflect their true colors, whether it be due to a (green?) filter, photo editing, or some other process.  Further support for this view can be found in Lech's observations.   

Hope this helps.


Best regards,

Mark Fox
Michigan

Offline DzikiZdeb

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Re: Patina on cleaned coins turns from brown to green
« Reply #5 on: March 10, 2022, 01:38:44 am »
Thanks to everyone for the answers. It seems to me that it is impossible for coins 1 and 2 to be stripped of their patina and then repatinated. The first - as Mr. Lech already wrote - is worn in the same places before and after cleaning, the surfaces of some worns have slightly increased, there are also new, relatively small ones. The second one already has a green patina over a large part of the surface before cleaning, so evidently it looks like only the brown layer has been removed.

As for the third one, it is difficult for me to judge - a lot has been removed here and maybe the brown layer was dirt, not patina?

Coming back to photography - the differences in colors seem really big, what would be the purpose of displaying photos taken with a green filter? After all, this is the basis for the buyer to return the coin - the coin actually looks different than in the photo. Or maybe the coins 1 and 3 are neither as brown as in the "before" photos, nor as green as in the "after" photos and the truth lies in the middle? How to explain case # 2 then?

Offline Jay GT4

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Re: Patina on cleaned coins turns from brown to green
« Reply #6 on: March 10, 2022, 07:15:19 am »
I agree with Mark.  Depending on lighting and exposure a coin can take on many different colors. 

Offline Callimachus

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Re: Patina on cleaned coins turns from brown to green
« Reply #7 on: March 10, 2022, 10:15:33 pm »
Dear Board,

 I am fairly certain the photographer(s) are at least partly responsible for the observed color changes.  The photos of the two Roman provincials (after the coins were expertly cleaned and possibly lightly smoothed), simply do not reflect their true colors, whether it be due to a (green?) filter, photo editing, or some other process.  Further support for this view can be found in Lech's observations.   

Mark Fox
Michigan

Yes - getting photos of coins that actually show how they look can be difficult. There are numerous variables, any one of which can mess things up if the photographer does not know what (s)he is doing, or how to compensate for the effect it has:

-- artificial light - different types of bulbs (LED, fluorescent, etc) and the different lighting they produce (daylight, soft yellow, etc).
-- natural light - direction (north, south, etc), cloudy, sunny, season, time of day, and perhaps latitude . . .
-- angle of coin in relation to the camera -- ideally they ought to be parallel.
-- angle of light source to coin.
-- background color.
-- camera white balance controls (my camera has daylight, incandescent, fluorescent, cloudy, flash, preset manual, auto.) Automatic is not always the best.
-- the amount of background color showing in the viewfinder compared with the amount of coin showing, can confuse the camera's light meter.
-- the proprietary algorithms of the software used in the various brands of cameras themselves. Some are better than others for coin photography.
-- playing around with the various color controls in your image processing software.

To show how different photos of the same coin can be, look at the 2 photos below.
The top one is the dealer's photo.
The bottom one is my photo of the same coin, and it shows quite accurately how the coin looks when I have it in hand.

Gordon M

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Re: Patina on cleaned coins turns from brown to green
« Reply #8 on: February 17, 2023, 09:05:48 am »
In my opinion, all 3 of those was chemically stripped with acid or lye and repatinated artificially.
it is true

Offline Joe Sermarini

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Re: Patina on cleaned coins turns from brown to green
« Reply #9 on: February 17, 2023, 10:17:15 am »
In my opinion, all 3 of those was chemically stripped with acid or lye and repatinated artificially.
it is true

No, it is not. And you have registered with a fake name and address. So, bye, bye, troll.
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