An exercise in cleaning - a Tiberius II Constantine follis, Antioch, "before" and "after"

[robinjojo]

Every now and then a coin comes our way that could do with some judicious cleaning.  Byzantine bronzes are often encrusted affairs that, with patient cleaning, primarily with distilled water, reveal more detail.  Each coin is really unique in terms of distribution of deposits, the nature of those deposit, the presence of corrosion and the quality of the strike, therefore requiring individual cleaning approaches.

This particular coin came by way of my local coin shop.  My local dealer had this coin for some time, so I was able to buy it at a fairly reasonable price of $35.  It's a solid coin without any indications of corrosion.

In terms of surface condition, it was apparent that some of the deposits were fairly soft and would come off rather easily with prolonged distilled water baths.  However, the green deposits were mostly rock hard and would not respond to this treatment.

My first step was to soak the coin for about two weeks in distilled water to remove, with cotton swabs and toothpicks as much of the softer deposits.  Soaking for prolonged periods, changing the water every now and then, caused the coin to darken somewhat.  My theory regarding that is that the loosened deposits might have been distributed over the entire surfaces of the coin, creating a overall darker effect.  Byzantine bronzes have a high copper content, much more so than Roman bronzes, which mostly had more a tin composition.  With this high copper content, my experience is that they darken quite rapidly compared to their Roman cousins.

When the distilled water treatment reached an acceptable point for me; detail, especially on the obverse became clearer particularly on the face and  consular robes, and a more even brown/green patina appeared.  I then had to address the issue of the hard, crusty green deposits.  With regards to these almost rock-like deposits the matter becomes one of compromise.  There is really no way to completely remove them without substantially altering the entire coin's appearance.  To me deposits and roughness are part of an ancient coin's character.  If a collector wants perfectly unblemished bright coins, he or she should look elsewhere.

So, what to do?  There are two options, chemical or mechanical (hand tool).  This is domain that requires some experience and judgement, judgement that has been obtained through trail and pretty disastrous errors.  I decided to use Naval Jelly, applied locally on some of the green deposits with a toothpick.  The Naval Jelly was only allowed about 10-15 seconds on the spots, with mechanical use of toothpicks and a dental hand tool, followed by a rinsing with distilled water.  The coin was examined and then repeated until I was satisfied.  The coin was then put into a distilled water bath for a few days, removed and thoroughly dried.  It was then left on a counter for many months (foggy memory here) and recently inserted into a safety flip.

The result is a compromise.  Detail, heretofore obscure, is revealed, yet much of the original roughness remains, as it should.  The hard green deposits were incrementally mitigated. Additionally the cleaning process did reveal some of the copper surface which will darken with time.  This is not a complete transformation, nor was it intended to be one.

Before: April 2022

Tiberius II Constantine, follis, Antioch, RY 6 (580/1AD).

Sear 448

15.69 grams

 

After, as of June 2023:

 

Edited June 28, 2023 by robinjojo

[Ancient Coin Hunter]

I see more detail in the left eye after cleaning. Everything else seems to appear more or less similar. But the good news is that the greenish deposits are not bronze disease. (Left eye being the emperor's left eye, not the right eye on the coin as viewed)

Edit: I like the patinated effect, and overall a bit more detail. I spent too much time cleaning LRBs when I first got back into hobby, so I became a bit goggle-eyed and had coin dreams.

Edited June 29, 2023 by Ancient Coin Hunter

[Al Kowsky]

3 hours ago, robinjojo said:

Every now and then a coin comes our way that could do with some judicious cleaning.  Byzantine bronzes are often encrusted affairs that, with patient cleaning, primarily with distilled water, reveal more detail.  Each coin is really unique in terms of distribution of deposits, the nature of those deposit, the presence of corrosion and the quality of the strike, therefore requiring individual cleaning approaches.

This particular coin came by way of my local coin shop.  My local dealer had this coin for some time, so I was able to buy it at a fairly reasonable price of $35.  It's a solid coin without any indications of corrosion.

In terms of surface condition, it was apparent that some of the deposits were fairly soft and would come off rather easily with prolonged distilled water baths.  However, the green deposits were mostly rock hard and would not respond to this treatment.

My first step was to soak the coin for about two weeks in distilled water to remove, with cotton swabs and toothpicks as much of the softer deposits.  Soaking for prolonged periods, changing the water every now and then, caused the coin to darken somewhat.  My theory regarding that is that the loosened deposits might have been distributed over the entire surfaces of the coin, creating a overall darker effect.  Byzantine bronzes have a high copper content, much more so than Roman bronzes, which mostly had more a tin composition.  With this high copper content, my experience is that they darken quite rapidly compared to their Roman cousins.

When the distilled water treatment reached an acceptable point for me; detail, especially on the obverse became clearer particularly on the face and  consular robes, and a more even brown/green patina appeared.  I then had to address the issue of the hard, crusty green deposits.  With regards to these almost rock-like deposits the matter becomes one of compromise.  There is really no way to completely remove them without substantially altering the entire coin's appearance.  To me deposits and roughness are part of an ancient coin's character.  If a collector wants perfectly unblemished bright coins, he or she should look elsewhere.

So, what to do?  There are two options, chemical or mechanical (hand tool).  This is domain that requires some experience and judgement, judgement that has been obtained through trail and pretty disastrous errors.  I decided to use Naval Jelly, applied locally on some of the green deposits with a toothpick.  The Naval Jelly was only allowed about 10-15 seconds on the spots, with mechanical use of toothpicks and a dental hand tool, followed by a rinsing with distilled water.  The coin was examined and then repeated until I was satisfied.  The coin was then put into a distilled water bath for a few days, removed and thoroughly dried.  It was then left on a counter for many months (foggy memory here) and recently inserted into a safety flip.

The result is a compromise.  Detail, heretofore obscure, is revealed, yet much of the original roughness remains, as it should.  The hard green deposits were incrementally mitigated. Additionally the cleaning process did reveal some of the copper surface which will darken with time.  This is not a complete transformation, nor was it intended to be one.

Before: April 2022

Tiberius II Constantine, follis, Antioch, RY 6 (580/1AD).

Sear 448

15.69 grams

 

After, as of June 2023:

 

Nice job ☺️! Your cleaning exposed more detail & the patina is now very attractive 😉.

[robinjojo]

Thanks for the comments.  I guess the overall message is one of establishing limits to cleaning, based on the characteristics of any given coin.  I could have continued with the chemical and mechanical cleaning processes, but I didn't want to totally alter the coin's appearance.  Some collectors might have taken the process to the point where the surfaces would be uniform in color and relatively smooth.  I've seen many bronze coins that have been cleaned and then given what my local coin dealer calls a "shoe polish" patina; I didn't want to do this for this coin, nor have I ever used shoe polish, apparently an old-time approach to change the color of a bronze coin after cleaning.

I have a few other Byzantine bronzes from group lot purchases that might be candidates for cleaning.  I'll post them if I do clean them, with before and after photos.

[Kaleun96]

The change in lighting and photography has had a bigger impact on the appearance than the cleaning so it's a bit difficult for me to judge what has changed if I'm honest, and I've been staring at it for a good minute or two! There are some minor changes but I can't be sure it's not just the lighting.

I'd be careful with the Naval Jelly though, it contains both phosphoric acid and sulfuric acid so I would think there's a risk of it removing the protective patina and allowing the surfaces to corrode further.

[robinjojo]

Yes, phosphoric acid needs to used with extreme care and only with experience handling this chemical.  I have not seen it triggering corrosion, but I do prolonged soaks in distilled water to neutralize and lingering effects.  I also keep a coin out for several months to monitor its surface condition.  

The lighting conditions for the second photo were somewhat brighter compared to those of the first.  However, there are differences in the level of detail between the two, especially with the obverse.  The reverse changes are indeed quite subtle.  The built up deposits were mostly removed.  I guess more could be removed with distilled water, but I'm leaving well enough alone.