Numismatic and History Discussions > Uncleaned Ancient Coin Discussion

How to Clean Silvered (not Silver) Coins

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Raymond:
Here's an example of what I have difficulty with:
On this coin offered by Forum, are the grey areas over the silver, or does it represent where the silver is worn away?
I think I may be too gentle with coins of this kind because rubbing away at the grey area does not seem to reveal more silver and attacking the silver does not appear to wear it away...
More elbow grease?  No matter what angle I use to look at coins of this nature, I just can't tell.
Comments?
Raymond

Johnny:
Honestly,  by the pics alone,  it looks like the silvering is worn away. Very hard to tell however

I do see spots  where the silver is obviously gone.....can you circle the areas in question,  this might help


EDITED......nice coin BTW 

SC:
Raymond,

I have been cleaning several of these recently.

It looks like you have both types of grey on your coin. 

There are some areas which appear dark grey in your photo which are likely where the silvering has worn off (on the obverse - Constantine's cheek, part of his neck, likely the highlights on his ear, dots on collar of his cuirass and highlights of some letters; on reverse - highlights of some letters, especially on the vexilatio/banner, head of captive to left, body of captive to right, thighs of both captives).  These areas are problematic.  This dark grey patina will start to wear through to copper colour if you brush or scrape too much.  Some soaks can make it discolor as well.

The lighter grey is very different, it should appear thick and crusty under magnification.  It is around all the details (ie letters, helmet and cuirass details, captives, exergue marks, etc.).  This is a form of encrustation which lies over top of the silvering and it is very likely that the silvering is absolutely fine under this stuff.  Therefore you can attempt to remove it.

Unlike Kevin I work these coins dry.  First I try the toothpick or bamboo skewer on the light grey stuff.  It rarely works at this stage but it does sometimes remove bits of the encrsutation.  It also lets you test the silvering.  Usually silvered coins circa AD 317-330 had a nice thick silvering so, depending on soil conditions, it is usually quite stable.

After this initial probing I take my tools -  1) a steel sewing needle in a pin-vise, and 2) an exacto-knife with curved-tip blade.  These need to be very, very sharp!  (I keep a sharpening stone handy and sharpen both tools every few minutes.)  Then, working with either a magnifying visor or a binocular microscope I gently probe away at the light grey encrustations.  You obviously need gentle touch and the right angle (very shallow, almost parallel to the surface).

When the grey is crusty (like it appears to be in many places in your photo) I find it will flake away quite easily.  The pin/needle works all around the letters and other details, the exact-knife or scalpel works in the fields and can be used to scrape the top part of the encrustation off detailed areas.

The pin/needle is my favourite tool.  If you do it properly it does not leave minute scratches through the encrustation, instead it usually pops the grey stuff off in small chunks.  You have to probe gently from all angles.  The exacto-kife/scalpel can cause the grey to flake away when used on the top layers.  It also cleans the fields nicely.

I usually go around the entire coin, from a variety of angles, once and then put it to the side again.  The temptation to keep at it should be avoided at all costs.  I have only ever screwed this up when I kept at it in a cleaning session long after the first pass (small scartches through the silvering between letters).  I have never scratched or messed up when being patient.

After going around with the steel tools once I usually go over the entire coin with toothpicks/bamboo.  This rarely removes more stuff but helps shine it up a bit and shows the results of the cleaning session better.

I must admit that I have never removed 100% of the grey encrustations this way.  I only go as far as I feel comfortable with.  Sometimes I will go back to a coin which I declared "done" months ago and give it another round.   Nevertheless, this route will easily take coins from little or no silvering to 90% or more showing.

There is another kind of grey encrustation which is much harder to deal with.  It is dark and smooth and at first glance looks like where the silvering has been worn through.  Even though it is relatively flat, when seen under mangification it is clearly on top of the silvering.  I think it is the light grey encrustation which has been worn down a bit.  It will also pop off and reveal nice silvering underneath but it is much harder to remove than the standard light grey encrustation because it is too smooth to get good purchase on and is quite hard.  Usuing the pin gently will occasionally scratch through this form of encrustation.  One good scratrch through is often all that is required as you then have a rough edge to catch on to clean the rest.  Often though it is the part I just leave.

I am not brave enough to Kevin's methods of long GG soak or sbbb on these yet.

Shawn

 



SC:
Here is an update on my mechanical cleaning of some silvered 4th century bronzes.  These AE3s are circa 316-317 and are from a small hoard I bought earlier this year.

Before photos of a IOVI CONSERVATORI AVGG.  I appologise for the crappy before photos.  I only had photos of a larger number of coins laid out so this cropped image is small and poor quality.

There is a good layer of medium-hard dry earth, especially on the obverse.  Under this is a green encrustation.  Under 20x magnification it looked like malachite yet it was clearly over intact silvering.  Parts were completely covered by the green, others had only partial covering.

Shawn

SC:
I only took good images of these coins when part way through the cleaning.

First I removed all dirt with toothpicks - either regular round toothpicks or ones I cut with an exacto knife to make a "scraper blade".  With patience all the major dirt was removed.  However, a thin layer of dirt still covered much of the coin - almost a "staining".

Then I set to work with a couple of exacto blades and a pin in pin-vise (all kept sharp with a whetstone).  All work was done under a 20x stereo microscope with a strong lamp to the side.

In these images you can see 2/3 of the obverse and 1/2 of the reverse cleaned in this manner.  You can see the different coverings.  Dirt over a fairly even green on the obverse.  Light dirt over sparse green on most of the reverse with some major green encrustations on Jupiter's head.

Shawn

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