Discussion in 'Ancient Coins' started by Theodosius, Jan 3, 2019.
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Thank you, this is great to read. I just came back from the holidays to see my precious Caligula As having bronze dicease! When looking for what to do against it, all the chemical solutions and treatments found online made me dizzy. Your explanation is straight forward, for a simpel lawyer like me good to understand. So i ordered the sodium online and will look for distilled water in a store somewhere. A bit anxious though, fearing the effect the treatment may have on my coin, but i think i need to treat it while the disadvantageous effects of the corrosion are limited. I think, because the obverse is corroded, the coin had BD earlier in its lifetime above the ground. I also wanted to order verdicare, but it seems to be out of stock. Is there a trustworthy alternative, any of you CT members have experience with?
here is a picture of the coin. Poor Caligula...:
I agree, the sodium sesq here would probably impact the non-BD patina. As SeptimiusT suggested, start with DW treatments as it will slowly leach out or neutralize the chlorides, along withsome mechanical cleaning with a toothpick to get the green powdery stuff away as much as you can through the process. It appears surface level and should result positively from ongoing mild treatment.
I feel for you & your Caligula!
You've got me on the edge of my seat now, John! Can't wait!
(Been reading to many of @lordmarcovan s threads. )
I noticed a few different effects. Some of the coins had BD under their patinas; these patinas flaked off and were lost. Some had areas where the patinas dissolved, while in other areas the patinas remained hard and intact. The fluffy green deposits sometimes turned into darker, hard, stable green deposits. Under the fluffy deposits were soft reddish areas that appeared to be bronze that was partly converted into some salt or oxide, these areas were pretty much lost as well over the treatment. It was necessary to remove any fluffy green stuff to expose the additional BD underneath or a crust would form encapsulating the BD and preventing it from being treated.
Finally, and most surprisingly to me, all the coins developed a distinctive blue coating, that I have seen before on other bronzes, and I suspect is the result of this treatment. It is not unattractive, and I suppose it could form naturally on bronze coins exposed to sodium compounds, but I can't help but feel these are BD coins in remission or recovery. I am not sure if there is a way to avoid this blue coating developing. It seems to be thicker on the downward side of the coin. I would alternate orientations each week to expose the two sides evenly to the solution which may have caused the blue coating to be more even between the sides. I am guessing some compound was forming in the solution through the action of the sodium compounds and it was floating around and reacting with the bronze surface of the coin.
After the extended soaking, I rinsed the coins repeatedly in distilled water and left them out on my desk for 3 months. I wanted to see if the BD returned and if any further changes occurred. So far, they all look to be stable. I think that multiple months were required for the treatment to be effective. After one month I was starting to think it would not work, but other coins came and took up my attention so it was easy to just keep treating them to see what would happen.
Here are three of the patients. I should have taken before and during pictures, but l did not realize starting out that this would turn into a case study.
Zeugitana, Carthage. 300-264 BC.
Æ 19mm 5.47gms. Sardinian mint.
Obverse: Wreathed head of Tanit left.
Reverse: Horse's head right; globe to right.
References: SNG Copenhagen 164.
A nice coin in hand, the blue coating it very obvious.
SICILY, Syracuse. Hieron II. 275-215 BC.
Æ27, 27mm, 16.66 gms. Struck circa 230-218/5 BC.
Obverse: Diademed head left.
Reverse: Horseman riding right, holding couched spear in right arm; IEPΩNOΣ in exergue.
Another case of the blues. This coin lost areas of patina around the edges and ended up with rougher surfaces.
SICILY, Syracuse. Timoleon and the Third Democracy. 344-317 BC.
Æ Hemidrachm, 24mm, 16.08 gms.
Timoleontic Symmachy coinage. 1st series, circa 344-339/8 BC.
Obverse: Laureate head of Zeus Eleutherios right.
Reverse: Upright thunderbolt; to right, eagle standing right.
This coin's entire patina was lost. The BD could be seen poking through small holes in the original patina. Over time the (very thin) patina flaked off. The bronze underneath is fairly smooth and the coin is still nice in hand. I believe this coin and the previous were on the way to complete destruction. I had two more small bronze coins where the BD was coming up from inside the coins. The BD was eventually stopped on them, but so much of the surface was lost that they were basically ruined as coins:
I did not even try to attribute these guys. The green looks light like BD, but it is hard and stable.
Could the blue coating on these coins be removed using some other chemical treatment? Maybe, but what other affects will that have on the bronze? It certainly does not come off from brushing with nylon or soaking in distilled water. I prefer to leave these alone for now. I think I have saved them, and that is good enough.
I think the lesson I learned is that BD can be stopped using this treatment but it takes time. The patina may or may not be affected, but you won't end up with a shiny copper coin when you are done at any rate.
Thanks for the advice everyone.
An update: picked the green stuff away and put the coin in DW. Will refresh it daily, for about a week. And then heat it, i guess. The mechanical picking resulted in the bronze to surface. On some small BD-spots the patina is now completely gone.
After the treatment with DW, i would like to apply something on it, to keep it safe. Online and in links in the post (eg bij Tiff) i read several methods (wax, verdi care). Might i ask for your help in this? What applicant do you think is best to apply to the coin? I am planning to put it in a close holder, so oxygene wont effect the coin.
Also, looking at the wizzard coin supply website, verdi care is still out of stock. Some alternatives are mentioned. Does anyone have any experience with the alternatives mentioned? Forum ancient coins mentions 'paste wax'. Is that the same, as renaissance wax?
How much time are you planning between the end of the DW treatment (when BD is no longer showing) and applying something? I'd recommend months as @Theodosius did to ensure the BD doesn't come back. Only then would I maybe apply something.
I have both and have used both. I have no positive or negative evidence as to my decision, but I prefer to apply the Verdicare to my recovered BD coins after in remission. On my other coins, I apply Ren Wax.
Good question Justin Lee. I have no specific thoughts about it. The method of Theodosius sounds like a very good one. I will follow that. Thank you!
Thanks for the great article! I will try this on my bronze. But I was wondering if you could tell me where you found sodium sesquicarbonate for that price? I have been looking around on Ebay, but I can't seem to find it.
I have received my sodium sesquicarbonate in the mail, and now I will begin treating my piece. Unfortunately, it is currently covered in renaissance wax. Could someone recommend to me a good way to remove it?
Soak a few minutes, dry it on a clean microfiber, repeat several times.
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