Bronze disease

Ken Dorney, posted: "I dont know what you are looking at. There isn't anything there."

Actually, new collector or not, the OP has a great set of eyes! Most of the surface is crystallized and he has picked out two spots.

Relish in this truth. Dont let one 'whacko' put any doubt to you. ( I never said you were a whacko Ken. However, in this discussion, you come across to me as one of the "Ex-Perts" around here. Your saving grace is the fact that you admitted you know nothing about metals). I assume you are new to ancients? There are plenty of weirdos out there, most of which know absolutely nothing but pretend to know all. (If the shoe fits...) Your coin is fine.

 

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I'm afraid it seems my comments were misinterpreted. My sincerest of apologies, I was not trying to disparage anyone in particular. The written word is a concept which is dying out, sadly. My kids communicate via instagram and other nonsense, but I will let my statements stand and hopefully people will try to interpret some good from them.

 

Thank you for your input @Insider A supported opinion is always appreciated and I'm glad we have that in the world otherwise we would all be sheeps.

I have placed this issue on ancient forums, maybe there are some experts there to shed some light about this.

 

This coin sold from the same dealer also got this weird structure on the surface? Much worse even.

Does anyone has any idea what this is? It does look like tiny crystals.

 

Usual disclaimer: I am not an expert. What I see is surface etching, presumably by burial conditions. I suppose it could be crystallization if that phenomenon occurs in bronze alloys, but it reminds me somewhat of Widmanstatten patterns which are seen when you etch certain alloys.

You asked earlier if it is something to worry about. Regardless of the cause of this surface appearance, I don't believe it is something of great concern. Even if it represents embrittlement of the coin, unless you're planning on dropping it or handling it roughly, I don't see why it would be a problem unless you just don't like the appearance.

 

Usual disclaimer: I'm no expert either.

The difference between the crystal pattern in meteorites and on these coins is the spacing between the crystals.

The two best guesses about these coins are:

1. Genuine coins with etched surface.
2. Cast counterfeits.

The fact that the coins came from the same source works for both choices above.

Let's see a few images of different parts of the edge.

Wow, my post entered in normal time. The problem may be fixed.

 

I’m far from an expert, but based on my understanding of “crystallization”, the process involves erosion of a metal or metal that has migrated and accumulated on the edges of the crystal lattice. If that understanding is correct, then there shouldn’t be a preferred orientation to the “crystallization”. The features on both coins appear strongly oriented, so I’m not yet convinced what we are seeing is “crystallization”. Flow lines from casting, perhaps?

 

@Silverlock flow lines is a good guess. Could also be the way the flan or dies were prepared. Some coins have flan preparation lines or adjustment lines:


Coin from a recent JA auction

And other coins have naturally rough surfaces from the way the dies and flan were prepared, or from die erosion.


Example: the obverse roughness from one of my Litras is a common feature due to die erosion, but may be mistaken by some as corrosion or post-mint damage.

And there are a whole other host of explanations for lines and marks on coin surfaces depending on the type of coin: for example, die rust, cracked dies, worn dies, double strikes, flow lines, adjustment lines, post-stike finishing (filing) by the mint workers, adjustment lines, etc.

The point is that OPs coin could have a dozen things that could explain those marks that may not be indicative of anything neferious. To jump to the conclusion that it is a cast without explaining in detail why @Insider thinks that is the case is unfair to OP...especially considering he is not exactly a proficient ancients collector.

I hear what he says, he's seen weird marks in cast forgeries, but those marks don't look to me like the typical marks one would see on a cast die that was damaged prior to it hardening. Another thing that makes me believe not a cast, I don't see the soapy look or the softness in detail (looks like normal wear to me) and I don't see the pattern of cast bubbles or die bubbles you see in casts, but rather irregular pattern typical of corrosion pitting and porosity one would get on a genuine coin during burrial.

Not to say OPs coin couldn't still be a forgery, but I'd be shocked if it was one.

My best guess, could be some sort of flow marks from die wear or erosion, or flow marks exaggerated by irregularities (non-uniform surfaces) in the flan made during flan preparation...but I won't say for sure as there's still a lot about the ancient minting process I still don't know (and I'll readily admit to that). I still have a lot to learn despite being a hardcore collector for 3 years.

 

Hopefully someday, modern inexpensive ( less than $2000) XRF devices will be available to determine the metal continent, so this reference may refer to a type of mix not used in ancient times, although I doubt it would matter much if copper was near correct proportions. Here is a reference for bronze of a CuAlFeNi mix, and on the page labeled 79 you ca see crosshatched crystals which occurred in a relatively low temperature phase , when Al was present in a 11-12% measure. The article is tough reading , but some one with the background to read and also corresponding background in composition of metals in such coins could draw a conclusion. Jim

https://content.sciendo.com/view/journals/afe/13/3/article-p72.xml

 

I always thought these strigillations - they are not uncommon - were made when preparing the flans, with sharp metal brushes. If they were occasioned by crystallization, you would expect seeing pictures of coins with crystals - pics before, and after, when the crystals were removed and left strigillitations on the bronze.

 

Maybe there some confusion over the term crystal. Most think of transparent material like Amethyst , Garnet, etc. But it is a chemical term of repetitive arrangements of atoms in a repetitive lattice that produces a macro structure arrangement that is visible. 90% of natural and man made substances we see are crystalline. So in your example, you would not see 'crystals' as I mention above, but an arrangement that reflected the internal arrangement of the metal atoms Just as metals we are taking about in coins are not 100% pure, neither is the arrangement of the crystals. Although not used in coinage, Bismuth and antimony, show the lattice and crystalline arrangements extremely easily.

https://www.thoughtco.com/how-to-grow-bismuth-crystals-606234
https://opentextbc.ca/chemistry/chapter/10-6-lattice-structures-in-crystalline-solids/

I have no coin in the discussion, and I will stop here as the physical chemistry of some metals are rather odd. Jim

 

@Sallent I should be clearer. I’m not suggesting anything nefarious. I was referring to the casting of the flan, not the final coin. If there were flow lines from the production of the flan, perhaps due to differential cooling or annealing or improper mixing or ?, then erosion of the coin surface might bring those features out.

 

Not talking down to anyone but let's not get into the weeds of fantasy. Just color me very frustrated and please forgive my VERY CRANKY AND DISAPPOINTED attitude at the moment.

Silverlock, posted: "I’m far from an expert, but based on my understanding of “crystallization”, the process involves erosion of a metal or metal that has migrated and accumulated on the edges of the crystal lattice. If that understanding is correct, then there shouldn’t be a preferred orientation to the “crystallization”. The features on both coins appear strongly oriented, so I’m not yet convinced what we are seeing is “crystallization”. Flow lines from casting, perhaps?" Absolutely NOT!



Sallent, posted: "Flow lines is a good guess. Could also be the way the flan or dies were prepared. Some coins have flan preparation lines or adjustment lines:

Unfortunately, none of your images have anything to do with the characteristic on the OP's coin so I removed them. The coin's surface is as original as a corroded, etched, or cast coin can be. Now we need to find out which is it.

And there are a whole other host of explanations for lines and marks on coin surfaces [Except these are not lines or marks!]epending on the type of coin: for example, die rust, cracked dies, worn dies, double strikes, flow lines, adjustment lines, post-stike finishing (filing) by the mint workers, adjustment lines, etc. Blah, blah, blah...and these also have nothing to do with the OP's coin.

The point is that OPs coin could have a dozen things that could explain those marks that may not be indicative of anything neferious. To jump to the conclusion that it is a cast without explaining in detail [Curious, What part of SPIDER-WEB CRYSTALLISATION did you miss?] why Insider thinks that is the case is unfair to OP...especially considering he is not exactly a proficient ancients collector.

Very true, Insider cannot tell a worn Fausta from a Crispus, a Bull from a Chimaera, or an Obol from a Hemiobol; however, he has probably looked at the surface of more ancient coins using a stereo microscope than 95% of the collectors/dealers in the World. Not bragging just fact! Additionally, on the two occasions where Insider disagreed with several prominent, long-time, very experienced Ancient coin dealers on the authenticity of a coin, the British Museum agreed the coins were counterfeit EACH TIME.

Now that we get that over with...

I hear what he says, [No you didn't] he's seen weird marks in cast forgeries, [Actually what I said was I've seen EXACTLY these marks on cast fakes and I've never seen an ancient bronze coin with spider-web crystallization - either genuine or counterfeit UNTIL NOW - on the OP's coin. Furthermore, as a member here, I added my observation. I NEVER said the OP's coins are counterfeit. What I said was they are unusual and he may wish to have them checked by someone who can at least attribute the coins as I have no clue what they are!] but those marks don't look to me like the typical marks one would see on a cast die that was damaged prior to it hardening. Another thing that makes me believe not a cast, I don't see the soapy look or the softness in detail (looks like normal wear to me) and I don't see the pattern of cast bubbles or die bubbles you see in casts, but rather irregular pattern typical of corrosion pitting and porosity one would get on a genuine coin during burrial.

As I already stated, it is possible that environmental conditions etched a cast planchet. Tooling did not make the marks and neither did the die.
Not to say OPs coin couldn't still be a forgery, but I'd be shocked if it was one.

My best guess, could be some sort of flow marks from die wear or erosion, NO, NO, NO! or flow marks exaggerated by irregularities (non-uniform surfaces) in the flan made during flan preparation...NO, NO, NO! but I won't say for sure as there's still a lot about the ancient minting process I still don't know (and I'll readily admit to that). I still have a lot to learn despite being a hardcore collector for 3 years."

Metal flow looks nothing like this - EVER!

Three years hardcore? Wow, you've come far in just three years. All this time from the knowledge and TONE of all your posts I thought you were a decade's old expert!

Pellinore, posted: "I always thought these strigillations - they are not uncommon - were made when preparing the flans, with sharp metal brushes. [I disagree 100%. Please give your reference for this or is it hearsay? Is it the same place the big word strilla-whatever came from. Perhaps you've spelled it incorrectly as I cannot find it on the Net. Thanks ] If they were occasioned by crystallization, you would expect seeing pictures of coins with crystals - pics before, and after, when the crystals were removed and left strigillitations on the bronze."

I'm going to let you guys research this as Desertgem has done. Here are some things to consider.

1. Ancient coins CRYSTALIZE over time. We see the results. The folks who would have taken the "before" image you suggest have been dead for centuries. Besides, they did not have the photographic equipment.

2. The size of the crystals forming in a liquid metal is largely dependent on the rate of cooling.

 

I think the fact it are no zig zag lines but parralel lines that it really looks like damage from cleaning.

I got a response from Joe Sermarini:

"Bronze does not crystallize, so that is not even a possibility. Other than edge filing, I have never seen parallel scratches or etching on a fake fhat indicated casting, nor have I ever heard anyone describe parallel scratches or etching as an indicator of casting. It is most likely, the result of rough cleaning."

"I have seen odd surfaces, similar to this, on coins found in fresh water. Still, I think rough cleaning is more likely."

And other members:

"I think the parallel lines may be the result of too extreme use of a wire brush in cleaning. Both coins have bee extensively cleaned, but they look authentic to me."

"To my eye, it looks like the result of acid etching of the surface. The result of a severe chemical cleaning process"

And a response at another forum from a moderator:

"If both these coins can from the same dealer, they might have used some type of chemical to clear them which also etched the metal. In my opinion they are both genuine."

 

Alright. Well, strigillation probably is not the right word (English being not my mother tongue - nor Latin). I should have said hatching, drawing closely spaced parallel lines in order to make the background of the coin dull. The design will shine more lustrous when the background is muted, hatched. Either by preparing the flan, or the die, with a hatching technique.

As for the crystallization, probably I don't know how this works (and I'm not the only one apparently). But there might be pictures of coins in various phases of crystallization.
Also, there might be pictures of coins that are doubtless forgeries showing these parallel lines.

 

Pavlos, posted: I think the fact it are no zig zag lines but parralel lines that it really looks like damage from cleaning. Already answered and disagreed with above.

I got a response from Joe Sermarini: Looked him up on the internet, not much to say.

"Bronze does not crystallize, so that is not even a possibility. Absolute, uninformed nonsense! See the BRONZE Indian cent that I posted above. THE METALS MAKING UP THE BRONZE ALLOY have separated into homogeneous crystals showing definite patterns. Ancient coins will not look as this does but I wished to prove that BRONZE can crystallize. Other than edge filing, I have never seen parallel scratches or etching on a fake fhat indicated casting, nor have I ever heard anyone describe parallel scratches or etching as an indicator of casting.
Perhaps that is because what you are referring to - parallel scratches - DO NOT occur on casts. I have not seen them either! Furthermore, I have NO CLUE why you think the OBVIOUS crystalline cross-hatched characteristic the OP has circled looks like a scratch. It is most likely, the result of rough cleaning."

"I have seen odd surfaces, similar to this, on coins found in fresh water. Still, I think rough cleaning is more likely."

And other members:

"I think the parallel lines [Look again, the pattern is made up of PERPENDICULAR cross-hatching.] may be the result of too extreme use of a wire brush in cleaning. [Disagree 100%] Both coins have bee extensively cleaned, but they look authentic to me."

"To my eye, it looks like the result of acid etching of the surface. The result of a severe chemical cleaning process" This IS one of the possibilities. No one has called the coins counterfeit yet. I have been given the attribution of the second coin. Aeolis, Myrina AE15 2nd - 1st Century. Now what an authenticator does is look for comparison pieces to see if the fabric is the same. I cannot post images in a timely fashion during the day. It is a computer glitch causing long waits and double posts. So, let's see what you guys can find.

And a response at another forum from a moderator:

"If both these coins can from the same dealer, they might have used some type of chemical to clear them which also etched the metal. In my opinion they are both genuine." So far, that is the correct assumption.

PS In the link above posted by DesertGem there are images and references to CRYSTALLIZATION of bronze alloys. So let's please put this part of our discussion to rest!

 

I still think that confusion over the non-scientific definition of crystal is part of the problem.
Crystals are the norm for the elements of the periodic chart. Notice in the chart below all of the metals used in coinage have crystal lattices.

http://periodictable.com/Properties/A/CrystalStructure.html

However, most people are aware that if they are trying to form metals, different heating and cooling time and temperature is need so the crystals align to either be strong or pliable, annealing is one name for that
Annealing (metallurgy), a heat treatment that alters the micro-structure of a material causing changes in properties such as strength

Surprisingly , there are many internet sources on ancient coinage and crystallization , but most are book quotes . Crystals do exist in chemical elements for sure. Whether the indicated structures in the current coin here, are or are not from crystals structural changes ,is the question.

Yes if some chemically active cleaner was used, it could etch the lesser/weaker bound faces of the metallic crystal ( as the coin metal is most likely not a single pure element, so some bonds would be weaker) but whether the faces show such I can not tell from the photo. Maybe a polarized metallurgy microscope could indicate it, but the article I quoted in the previous post did use high level equipment and should be quite accurate. Whether a Chemical cleaner used, Natural soil conditions over centuries, or a tampered coin, I have no idea. Jim

 

@Insider I explained to you why Ancient bronze coins can't crystallize because of the content of many other metals and impurities giving the crystals no room to grow. In the US indian cent the composition is highly controlled consisting of only copper and tin or nickel?

Anyway I think the discussion can end, I believe the coin is authentic and just bulk cleaned with chemicals causing surface etching. I didn't pay much and if somehow I find out in 10 years time that it does is a fake cast then it is not even a waste of money but a valuable lesson for everyone because it had tricked many many collectors