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Some myths and misunderstanding about toning
Rob790
Posts: 547 ✭
This is not a thread necessarily about NT or AT toned coins, instead this is a thread to correct some statements I've read here in past threads that are just plain wrong about some aspects of toning. I just want to educate and contribute. A better understanding of toning seems to be of interest to a significant number of members here.
MYTH 1 : The lack of toning around the fields of outer devices (especially the stars and date) of Morgan Dollars is due to the way the coin is in contact with the mint bag or whatnot that is causing the toning.
This is totally wrong! According to the above posed theory, the toning would not block just part of the fields around the devices but the entire perimeter around the device. If you actually look at these, the toning is ONLY blocked in the fields that extend towards the edge of the coin. So what is causing this? As someone who has studied solid state physics and worked in clean rooms (where we built microprocessors), it is a well known fact that the rate at which a metal reacts has not only to do with it's composition but also with it's metallic alignment and structure to the chemicals attempting to react with it. If you look closely at one of these toned Morgans (this is just the example used here but this effect is seen on numerous other issues) and look very carefully at the area where no toning is seen, you will notice that these areas are areas where the die caused excessive pressure on the planchet, essentially stretching and stressing the metal of the planchet beyond that seen elsewhere on the coin. These area have a stretched look to them. These stretch marks are only seen going out from the devices and towards the edge of the coin as this is what would be expected as the planchet is squeezed between the dies. So what does this do to the coin? 1) it "work hardens" the metal more so than other sections of the coin and 2) this extremely work hardened metal has a different metallic structure than the rest of the coin (same composition of course but a different structure on the atomic scale) that makes it more resistant to chemical reactions like toning. Some areas with the stretch mark can tone, it is not untoneable - just more resistant to toning. But from my observation, if you see these tone free areas, you should see the "stretch marks" in the untoned areas. Go ahead and look for yourself under a high power scope if you have an example handy.
So are these tone free areas an indicator of an NT coin? No, if the coin doc is able to tone his/her coin with little or no heat then this area will remain resistant to toning and not tone. But if the doc has to apply a lot of heat then this excess heat would change the metallic structure of these stretched areas to lose its tone resistant quality and these areas would tone just like the rest of the coin. The type of chemical used may also be able to tone these areas, it just all depends. But seeing these tone free areas are no guarantee that the coin's toning has not been doctored. Oils or grease (like the ones on your fingers) and any surface substance can also inhibit toning, so a tone doctor could just cover these areas with some inert material, tone the coin and remove the insert substance to duplicate this effect. Look for the stretch marks as a clue but remember that this should be only one point to consider. Look for the overall look of the coin if you are trying to make a determination of AT/NT. NT/AT determination is more of an art in that it should have a familiarity to it that can only really be understood from looking and studying many 'known' material.
MYTH 2: Theories as to the color progressions as the thin film grows thicker are often incomplete or just plain wrong.
I read just the other day someone saying the toning progression is "ROYGBIV" and at numerous other times others saying something closer to the truth but short of the whole story.
ROYGBIV is just plain wrong. This explains a totally different optical effect that has nothing to do with thin films. Toning has rainbow colors but NOT a rainbow's progression of colors.
The colors seen from a thin film is a function of four things: the color of the coins surface, chemicals (if any) on the coins surface, the thin film interference effect and the inherent color of the thin film. As most transparent or translucent thin films grow thicker, they will become black. The inherent color of the thin film will have an effect on the shade and tint of the thin film interference effect.
The primary color progression for silver (this means silver colored surfaces, so cupper/nickel US alloy applies here) is as follows:
No toning - Light Gold - Banana Yellow - Burgandy - Dark Blue - Light Blue - Silver - Lemon Yellow - Red - Blue - Green - Yellow - Red - Green .... Black
The primary color progression for copper (actually means copper colored surfaces) is as follows:
No toning - Orange (Red copper color) - Burgandy - Dark Blue - Light Blue - Silver - Lemon Yellow - Red - Blue - Green - Yellow - Red - Green .... Black
Please note that the colors <Yellow - Red - Green> keep repeating- becoming grayer after each repeat until it turns black.
The Orange color as seen in the copper color progression is the same color seen in copper coins with the Red designation on PCGS holders. A copper coin stripped of this thin film toning will be salmon pink in color, the natural color of the copper alloy used in coinage. This is why dipped copper coins look so unnatural (besides the lack of luster). Also the chemicals used in dipping will inhibit natural looking thin film growth and you'll get all kinds of funky chemical color patterns that look AT and are a tell-tell sign of a dipped coin. I would in general not dip a copper coin. The dipping will inhibit a natural looking thin copper-oxide film seen in real Red designated coins.
Practically every color imaginable is in this toning progression but they may be within a very narrow thickness range and not easily obtained or maintained (I use this terminology because the thin film on the coin can continue to grow in thickness even after being removed from the original source of toning and the colors can still change!). Purple, Pink, etc … they're all in there somewhere.
The color progression is not necessarily a sign of an NT or AT coin. This is just the requirement of optics and the physiology of the human eye that cause us to perceive these colors. And this progression is only really visible if the thin film's thickness grows gradually in thickness across the coin with a thinner film in one region and growing to a thicker film in another region. Sudden changes in film thickness will cause sudden changes in colors that do not correspond to the color progression as described above.
Here is a picture that captures the color progression for thin films:
This is an optical effect called a Black-Light Sandwich, it clearly shows the color progression you would see for any transparent/translucent thin film phenomena as the film grows thicker. The center of the picture is where the film is the thinnest, and away from the center, the film grows thicker (just ignore the vertical black bar, an unavoidable side effect of the Black-Light Sandwich). In coins, as you can see in the picture, the film grows grayer as it grows thicker- in coins this will eventually lead to black after only a few repetitions of the <Yellow - Red - Green> colors. Hard to tell from the picture, but between the first blue zone and the next outer yellow zone is where the silver color resides. I hope this helps people to understand the color progression in a real way. Also hard to see, but between the red and green bands that repeat are yellow zones.
The next diagram corresponds to a cross sectional view of a coin and thin film that would produce a bulls-eye type toning, like the one seen in the above picture of the Black-Light Sandwich. The blue color on top of the coin represents the transparent thin film with an exaggerated profile to emphasize its contour.
From my observation, the thin film can continue to grow even after it has been removed from the 'source' of toning - not always and not at the same rate. Most toning is an oxide of some sort and usually needs oxygen, heat (even room temperature) and time to continue growing. That is not to say that they will grow indefinitely, they will grow until they are no longer able to oxidize. Put in a very simple way, they will grow till the film chokes off the supply of oxygen to the unoxidized metals - a very complex issue. So not all toned coins will eventually turn completely black.
I am always amazed when I see an original Red copper coin from the 19th century, these are amazing coins in that they have been able to resist further oxide growth. I think they give us hope that some of our toned jewels will still be with us into the next century. Like most things, it's really a gamble with unknown odds.
I hope this helps some to understand the complex nature of toning.
MYTH 1 : The lack of toning around the fields of outer devices (especially the stars and date) of Morgan Dollars is due to the way the coin is in contact with the mint bag or whatnot that is causing the toning.
This is totally wrong! According to the above posed theory, the toning would not block just part of the fields around the devices but the entire perimeter around the device. If you actually look at these, the toning is ONLY blocked in the fields that extend towards the edge of the coin. So what is causing this? As someone who has studied solid state physics and worked in clean rooms (where we built microprocessors), it is a well known fact that the rate at which a metal reacts has not only to do with it's composition but also with it's metallic alignment and structure to the chemicals attempting to react with it. If you look closely at one of these toned Morgans (this is just the example used here but this effect is seen on numerous other issues) and look very carefully at the area where no toning is seen, you will notice that these areas are areas where the die caused excessive pressure on the planchet, essentially stretching and stressing the metal of the planchet beyond that seen elsewhere on the coin. These area have a stretched look to them. These stretch marks are only seen going out from the devices and towards the edge of the coin as this is what would be expected as the planchet is squeezed between the dies. So what does this do to the coin? 1) it "work hardens" the metal more so than other sections of the coin and 2) this extremely work hardened metal has a different metallic structure than the rest of the coin (same composition of course but a different structure on the atomic scale) that makes it more resistant to chemical reactions like toning. Some areas with the stretch mark can tone, it is not untoneable - just more resistant to toning. But from my observation, if you see these tone free areas, you should see the "stretch marks" in the untoned areas. Go ahead and look for yourself under a high power scope if you have an example handy.
So are these tone free areas an indicator of an NT coin? No, if the coin doc is able to tone his/her coin with little or no heat then this area will remain resistant to toning and not tone. But if the doc has to apply a lot of heat then this excess heat would change the metallic structure of these stretched areas to lose its tone resistant quality and these areas would tone just like the rest of the coin. The type of chemical used may also be able to tone these areas, it just all depends. But seeing these tone free areas are no guarantee that the coin's toning has not been doctored. Oils or grease (like the ones on your fingers) and any surface substance can also inhibit toning, so a tone doctor could just cover these areas with some inert material, tone the coin and remove the insert substance to duplicate this effect. Look for the stretch marks as a clue but remember that this should be only one point to consider. Look for the overall look of the coin if you are trying to make a determination of AT/NT. NT/AT determination is more of an art in that it should have a familiarity to it that can only really be understood from looking and studying many 'known' material.
MYTH 2: Theories as to the color progressions as the thin film grows thicker are often incomplete or just plain wrong.
I read just the other day someone saying the toning progression is "ROYGBIV" and at numerous other times others saying something closer to the truth but short of the whole story.
ROYGBIV is just plain wrong. This explains a totally different optical effect that has nothing to do with thin films. Toning has rainbow colors but NOT a rainbow's progression of colors.
The colors seen from a thin film is a function of four things: the color of the coins surface, chemicals (if any) on the coins surface, the thin film interference effect and the inherent color of the thin film. As most transparent or translucent thin films grow thicker, they will become black. The inherent color of the thin film will have an effect on the shade and tint of the thin film interference effect.
The primary color progression for silver (this means silver colored surfaces, so cupper/nickel US alloy applies here) is as follows:
No toning - Light Gold - Banana Yellow - Burgandy - Dark Blue - Light Blue - Silver - Lemon Yellow - Red - Blue - Green - Yellow - Red - Green .... Black
The primary color progression for copper (actually means copper colored surfaces) is as follows:
No toning - Orange (Red copper color) - Burgandy - Dark Blue - Light Blue - Silver - Lemon Yellow - Red - Blue - Green - Yellow - Red - Green .... Black
Please note that the colors <Yellow - Red - Green> keep repeating- becoming grayer after each repeat until it turns black.
The Orange color as seen in the copper color progression is the same color seen in copper coins with the Red designation on PCGS holders. A copper coin stripped of this thin film toning will be salmon pink in color, the natural color of the copper alloy used in coinage. This is why dipped copper coins look so unnatural (besides the lack of luster). Also the chemicals used in dipping will inhibit natural looking thin film growth and you'll get all kinds of funky chemical color patterns that look AT and are a tell-tell sign of a dipped coin. I would in general not dip a copper coin. The dipping will inhibit a natural looking thin copper-oxide film seen in real Red designated coins.
Practically every color imaginable is in this toning progression but they may be within a very narrow thickness range and not easily obtained or maintained (I use this terminology because the thin film on the coin can continue to grow in thickness even after being removed from the original source of toning and the colors can still change!). Purple, Pink, etc … they're all in there somewhere.
The color progression is not necessarily a sign of an NT or AT coin. This is just the requirement of optics and the physiology of the human eye that cause us to perceive these colors. And this progression is only really visible if the thin film's thickness grows gradually in thickness across the coin with a thinner film in one region and growing to a thicker film in another region. Sudden changes in film thickness will cause sudden changes in colors that do not correspond to the color progression as described above.
Here is a picture that captures the color progression for thin films:
This is an optical effect called a Black-Light Sandwich, it clearly shows the color progression you would see for any transparent/translucent thin film phenomena as the film grows thicker. The center of the picture is where the film is the thinnest, and away from the center, the film grows thicker (just ignore the vertical black bar, an unavoidable side effect of the Black-Light Sandwich). In coins, as you can see in the picture, the film grows grayer as it grows thicker- in coins this will eventually lead to black after only a few repetitions of the <Yellow - Red - Green> colors. Hard to tell from the picture, but between the first blue zone and the next outer yellow zone is where the silver color resides. I hope this helps people to understand the color progression in a real way. Also hard to see, but between the red and green bands that repeat are yellow zones.
The next diagram corresponds to a cross sectional view of a coin and thin film that would produce a bulls-eye type toning, like the one seen in the above picture of the Black-Light Sandwich. The blue color on top of the coin represents the transparent thin film with an exaggerated profile to emphasize its contour.
From my observation, the thin film can continue to grow even after it has been removed from the 'source' of toning - not always and not at the same rate. Most toning is an oxide of some sort and usually needs oxygen, heat (even room temperature) and time to continue growing. That is not to say that they will grow indefinitely, they will grow until they are no longer able to oxidize. Put in a very simple way, they will grow till the film chokes off the supply of oxygen to the unoxidized metals - a very complex issue. So not all toned coins will eventually turn completely black.
I am always amazed when I see an original Red copper coin from the 19th century, these are amazing coins in that they have been able to resist further oxide growth. I think they give us hope that some of our toned jewels will still be with us into the next century. Like most things, it's really a gamble with unknown odds.
I hope this helps some to understand the complex nature of toning.
0
Comments
When we are planning for posterity, we ought to remember that virtue is not hereditary.
Thomas Paine
Dan
mcinnes@mailclerk.ecok.edu">dmcinnes@mailclerk.ecok.edu
and it sets us apart from practitioners and consultants. Gregor
<< <i>Excellent thread! That's interesting information... I'm one of those who wrongly assumed that a lack of toning on one side of the stars on a Morgan dollar meant that it was NT. I'll remember what you wrote when looking at Morgans. >>
It's a common mistake. The ANA video on artificial toning goes into it a bit more and talked about how it's a very unreliable marker.
Russ, NCNE
Of course, for their volume submitters, 500+ coins/month, the "educated guess", becomes more of a business decision.
<< <i> It has the one key characteristic that most look for. >>
What characteristic is that? A PCGS holder?
When we are planning for posterity, we ought to remember that virtue is not hereditary.
Thomas Paine
<< <i>What characteristic is that? A PCGS holder? >>
You a sharp cookie.
Russ, NCNE
Thanks Rob,
-mark
Photos of the 2006 Boston Massacre
I hearby nominate this for a POTD nod.
Any seconds ?
What characteristic is that? A PCGS holder?
lol
On the bottom of this page
et al. seen a few good toning debates come through in the past. exhaustive reads i tell ya.
...where are all those guys.....lol
Because collectors have seen books and videos trying to educate the collector on toning progression, I have a question on the following:
<< <i>
I read just the other day someone saying the toning progression is "ROYGBIV" and at numerous other times others saying something closer to the truth but short of the whole story.
ROYGBIV is just plain wrong. This explains a totally different optical effect that has nothing to do with thin films. Toning has rainbow colors but NOT a rainbow's progression of colors.
>>
Could you please comment further on how ROYGBIV is a different optical effect and not appropriate to describe the toning effect on coins. Thanks again, most interesting.
Kyle
its all rock solid science really.
its how we interpret it i guess is where we debate.
<< <i>This is the best post I have seen on this forum in months! Thanks so much.
Because collectors have seen books and videos trying to educate the collector on toning progression, I have a question on the following:
<< <i>
I read just the other day someone saying the toning progression is "ROYGBIV" and at numerous other times others saying something closer to the truth but short of the whole story.
ROYGBIV is just plain wrong. This explains a totally different optical effect that has nothing to do with thin films. Toning has rainbow colors but NOT a rainbow's progression of colors.
>>
Could you please comment further on how ROYGBIV is a different optical effect and not appropriate to describe the toning effect on coins. Thanks again, most interesting. >>
---
Well, I didn't delve into it because it is a little complex. But I'll try to explain.
ROYGBIV is as most people know is a shorthand for the color progression in a rainbow- Red-Orange-Yellow-Green-Blue-Indigo-Violet and apply to the colors seen when white light is diffracted by some medium like a prism. Each color is a slice from the white spectrum. In this since it is a pure color with no mixing from other parts of the spectrum. Kind of like picking out a single violin from a symphany.
In contrast, a thin film is the inverse of this- a completely opposite effect. The thin film is a subtractive process that causes certain parts of the spectrum to disappear- so you actually are seeing all of the parts of the light spectrum minus the part 'absorbed' by the thin film. It involves the addition of different optical colors that goes against our normal understanding of how colors mix. If you were to take paint and mix them all together- you'd get a brown or black color; however, if you were to mix a bunch of optical light colors together, you'd get white! Continuing the symphany analogy, this would be like blocking out and turning a deaf ear that single violin and listening to the rest of the instruments. The combination of each of those instruments add only a small part of the whole musical experience and the combination of all of them has a different effect overall than any single instrument. Makes any sense??
Anyways, I hope this helps.
I don't own the coin in my icon, but I'd guess it's AT. Regardless, I think it's very attractive.
Thanks again.
Tom
Here is the best link that I've found explaining the chemistry and physics behind toning. Link.
<< <i>The oxidation product of silver is a physical entity, that is, it has mass. Toning, however, is not a physical entity that has mass. Let me explain this in as concise a manner as possible. The surface of the coin will develop a very thin layer of silver sulfide on it over time. This layer is so thin that a beam of light aimed at the coin, from Point A, in the figure below, splits into two parts, or phases, at Point B. One part goes through the layer of silver sulfide and strikes the surface of the coin at Point E. This is then reflected back to the viewer. The other part (phase) of the light beam reflects off of the silver sulfide layer and never penetrates it. This light is also reflected back to the viewer. However, although these two parts (phases) of this single light beam travel at the same speed and were generated at the same time (from a light source like a lamp) one part of the beam of light travels a longer distance than the other part. The part of the beam that traveled through the silver sulfide to strike the coin and was then reflected back to the viewer has actually traveled twice through the silver sulfide-once from the lamp to the surface of the silver sulfide and then to the surface of the coin and out to the viewer (A-B-E-F-G) while the other beam reflects off the surface of the silver sulfide and to the viewer (A-B-C). This total distance through the silver sulfide is on the order of nanometers (nm). The difference in the total distances that these two parts of the light beam travel is, obviously, incredibly small. However, it is precisely because they are so small that we see toning. Toning is the result of the refraction of the light beam through the silver sulfide and the resulting interference with the other portion of the beam that did not penetrate the silver sulfide-this is called thin film interference and is the exact same phenomena that causes oil on water to look like a rainbow. Because the silver sulfide is not of uniform thickness we see different colors on the coin. Once the layer of sulfide becomes a certain thickness the light no longer penetrates through to the coin's surface and the toning becomes dark or brown/black. >>
For copper coins just substitute copper sulfate for silver sulfide in the above paragraph.
Hoot
Please note that the colors <Yellow - Red - Green> keep repeating- becoming grayer after each repeat until it turns black."
Great post. Your toning progression for copper was something I always wondered about. Most copper collectors can figure out the early stages, from orange to dark blue, by looking at a lot of MS coins (the image below illustrates the first four stages). But when it comes to copper proofs I always wondered how the last colors on your chart progressed. For those who collect deeply toned IH proofs this makes a lot of sense -- green is highly sought after due to its rarity. I would have guessed that the Light Blue stage (aqua) came before the Dark Blue. Great food for thought...
The center of the coin has the thinner thin film and grows thicker as it goes towards the perimeter. Note that the dark blue/purple comes before the light blue and then blends into silver as the film grows thicker.
Here is a picture of the obverse that very dramatically shows the color progression. Remember that the center has the thinner film and the edge has the thicker film.
I believe a board member owns this coin and I hope he doesn't mind my using his images that I got off eBay.
Shylock, that is a great progression of coins you pictured! I like it and it very clearly shows the colors that I'm talking about.
FOR SALE Items
Again, superb post.
Hoot
My icon just looks too good to be true- it doesn't look right. I find that natural toned coins have a sort of 'dirty' look to them that comes from the texture and interplay of the toning colors. Besides, if a coin exhibits the correct color progression or not has little to do with it's being NT or AT, the color progression is a result of the thin film and is indifferent to it being NT or AT.
shylock
Expert Collector
Posts: 3764
Joined: Feb 2001
Wednesday July 14, 2004 9:38 AM
"No toning - Orange (Red copper color) - Burgandy - Dark Blue - Light Blue - Silver - Yellow - Red - Blue - Green - Yellow - Red - Green .... Black
Please note that the colors <Yellow - Red - Green> keep repeating- becoming grayer after each repeat until it turns black."
Great post. Your toning progression for copper was something I always wondered about. Most copper collectors can figure out the early stages, from orange to dark blue, by looking at a lot of MS coins (the image below illustrates the first four stages). But when it comes to copper proofs I always wondered how the last colors on your chart progressed.
==========================================================================
For those who collect deeply toned IH proofs this makes a lot of sense -- green is highly sought after due to its rarity. I would have guessed that the Light Blue stage (aqua) came before the Dark Blue. Great food for thought...
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
great thread this toned coin thread!!!!!!!
and paul i agree really rare and most highly sought after these original green toned proof indian cents
most have never even heard let alone seen as such
michael
<< <i>For copper coins just substitute copper sulfate for silver sulfide in the above paragraph. >>
I believe that this would be copper sulfide not copper sulfate. The thing is that toning caused by contact of the coin with the canvas storage bag [and thus a reaction of the coin metals with residual chemicals used in the manufacture of the canvas] is different than toning that might be caused by atmospheric contaminants. First off, depending on where you live there is not a lot of hydrogen sulfide just floating around out there. Also these days especially there are many other contaminants fron auto exhaust, power plants and industrial activity that weren't present 100 years ago. Also at least for Morgans which contain both copper and silver, the silver reacts faster with sulfur sources than copper does. With other contaminants say NOX or cyanide just the opposite is true.
MY COINS FOR SALE AT https://www.pcgs.com/setregistry/collectors-showcase/other/bajjerfans-coins-sale/3876
Ken
--------T O M---------
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Toned Coins for sale @ tonedcointrader.com
I'd also like to thank oldcameoproofsguy for quoting my work and linking my web site in this toning discussion.
One thing that everyone should keep in mind is that while toning is based upon science, it is not a completely controlled reaction and, as such, is not perfectly predictable.
In honor of the memory of Cpl. Michael E. Thompson
*******************************************************************************
Looks like some good stuff.
Thanks TWODOGS for the tip.
Very nice post Rob790. I think the above statement you made is THE most significant aspect in determining whether the coin you are viewing is original or bunk. I believe most people who know what they're looking at with regards to toned coins can just glance at a coin and make a AT/NT determination in a couple of seconds in most cases.
There is no substitute for experience.
dragon