Sunnywood Color Q&A

Sunnywood

I received an e-mail this morning from a collector who had the following question:

Was hoping you could explain the "rare third cycle gold, which comes after emerald green in the progression"...

Trying to understand WHY these colors are unique & "rare".



Here was my answer. I thought perhaps others would be interested:

The colors on coins come from the thin film interference phenomenon, in which two beams of light bounce of the coin - one from the upper surface of the toning layer, and one from the underlying silver. The two beams interfere with each other, selectively cancelling and reinforcing various wavelengths. That in turn interacts with the way our eye perceives color, with the retina having three "cone" type photoreceptors that respond differently to different wavelengths.

The way the numbers fall out when you do the math, which I have done, the progression of colors repeats as the toning layer gets thicker (the "cycles") ... but it does not repeat exactly the same way. Also, at different points in the progression, the colors are not all equal, in the sense that a small incrememnt in toning layer thickness may not affect the perceived color at one point in the progression, whereas perhaps at another point in the progression, a small increment in the thickness of the toning layer changes the color dramatically.

It is most common to see first cycle colors on coins. Most typical toned coins have first cycle colors, and just reach into the second cycle (whien you start getting blue at the rims). The second and third cycle colors take longer to develop. By the time you get out to a color like 3rd cycle "R" emerald green, there's a lot of toning going on. Other than bag-toned Morgans, and small-diameter album-toned coins (dimes, for example), it's relatively rare to get 3rd cycle colors on most coins.

The emerald green is a particularly beautiful color. The first cycle does not have a green color. The second cycle has the H "pale mint green" color, which is unique but sometimes difficult to pinpoint. (It reminds me of the so-called "green flash" in a sunset, although that is of course produced by refraction, not by interference). The third cycle has the powerful bright R "emerald green," so strongly desired by Morgan collectors. And the fourth cycle has the deeper darker V "forest green."

Bag-toned Morgan dollars, which are larger size silver coins that were in many cases stored undisturbed for decades, are the most likely place to find large swatches of emerald green, but it is still relatively rare.

Immediately after the third cycle emerald green, there is a very beautiful rich gold color, followed by a rich magenta. At this point in the cycle, thin increments in the toning layer seem to affect the color quickly. So once you get enough thickness to get past the emerald into the gold, it doesn't take much more to turn it into the magenta. For each color in the progression, there may be coins out there that are predominantly toned in that color ... but it's really hard to find coins that have large areas of this 3rd cycle gold, probably for the reason that I have given.

I hope this helps,

Sunnywood

P.S. Here is the famous 1881-S PCGS MS68 CAC from the Sunnywood Collection,
now owned by collector extraordinaire Bob Simpson,
which will be offered at auction by Legend on October 2nd.

Note the beautiful emerald green going straight across the face of the coin. The color progression goes top to bottom on the obverse, so you can see the 3rd cycle gold below the emerald green, which then transitions to magenta. There are other coins that show the 3rd cycle gold a bit better, but this coin gives a typical demonstration:

ElmerFusterpuck

Always enjoy your 'colorful' posts! Would this one be hitting the 3rd cycles? It's probably my 'greenest' toner, with the splash of magenta across the cheek.

Sunnywood

You're well into the 4th cycle there. The least toned area (lower left, left of the date, at the rim) is actually already at H in the progression, rather than being untoned (which it appears at first glance). I can tell this by how it progresses from there to the emerald green, which is clearly visible from star 2 over to the date.

There is 3rd cycle gold in the brightly lit area to the left of Liberty's neck. As is often the case, the 3rd cycle gold is intermingled with magenta. There is also 3rd cycle gold in the recesses of Liberty's ear.

The primary colors covering the rest of the coin range from 3rd cycle T magenta to 4th cycle V deep green (forest green).

Sunnywood

Boosibri

Wonderful post

WingedLiberty1957

Great post.

I have a Morgan with a bit of green ...


And Sunnywood's progression mapping ...

drwstr123

S/W...thx.

Crazy4Coins

Hi Sunnywood,

Thanks for your post. I've compared this dime to your color progression chart and came to the opinion that it shows the toning cycle from A of the first cycle through just the beginning of T in the third cycle.

Am I correct?

ranshdow

Sunnywood, first this is a terrific education. Thank you.

WingedLiberty, thank you for that color chart. I don't know if this has been published elsewhere, but this is certainly the first I've seen or heard of it.

C4C, I'm seeing through Q-R myself. That's a great dime by the way.

Crazy4Coins

How about this one? Am I seeing some of the 4th cycle transitions?

Sunnywood

Hi Crazy4Coins, you are absolutely right about the dime. It runs from AB at the center right through the progression out to R, and then basically goes terminal. Sometimes you see that jump from the middle of the progression right out to terminal (Y or Z on the chart), especially at the periphery of small diametr album toned coins such as dimes and half dimes. The colors are a bit subdued on this coin, rather than being vivid and reflective, but you can pretty much follow it from A to R, maybe the beginnings of T as you suggest, and then dull terminal toning at the rims.

On your SLQ, the bright center appears untoned at first, but if you observe how it progresses from there to the emerald green at the right border, you realize we are starting at the lightest point of the 2nd cycle (H or I on the chart), rather than starting at true untoned O. This is further supported by the fact that we do not see the typical F cobalt blue toning anywhere in between. So we start at H or I, and progress out to R emerald green. If you look at the left side, it goes further. Look at QUAR, and you see we go past the emerald green, into 3rd cycle T magenta at the rim. I think we stop just at the end of the 3rd cycle, and don't quite see any 4th cycle colors.

For everyone else reading, of course album-toned coins develop toning from the outside in. So typically, the lowest toning category will be at the center of the coin, and the toning will progress radially outward to the rims. Album toners often have a less-toned reverse, but it is usually the case that the most toned point on the obverse rim will correspond to the most toned point on the reverse rim when you flip the coin over. Smaller diameter coins like dimes have less distance to the center, so it is often the case that even the centers reach higher toning levels. A larger coin might be more likely to have an untoned center, while a dime might be more likely to start well into the 1st cycle or beyond at the center, and progress outward from there.

ranshdow, I first created that chart in Lotus 1-2-3, after actually working out the mathematics of the wavelength interference patterns in a spreadsheet, using the peak sensitivity wavelengths for our three cone-type receptors, and with an understanding of the way we perceive color (the subtractive property of light), I was able to derive and predict the progression from scratch. I did this away from my coins, and then was thrilled to see that the model matched what I actually saw on the coins. I first published it here on these message boards a number of years ago, although I had worked it out some time before that.

Sunnywood

metalmeister

Hail the Sunnywood toners


PCGS MS65

drwstr123

Copper the same?

lostincoins

Here is a very toned coin from an album, it resided there for 45+ years and is still there.

Sunnywood

Great question about copper. The basic principle is the same, in that one beam of light bounces off the toning, and the other off the underlying surface of the copper coin, and they interfere with each other, producing colors. But there is a differrence ... the reason copper looks reddish-orange is that it absorbs some wavelengths of light, and reflects others. Therefore, the beam that bounces off the underlying copper surface will have had some of its light absorbed by the copper. This reduces the prevalence of the interference effect and changes the net color. Another way to say this is that in many cases, the "color" of the copper may overwhelm the thin film colors. But, you can still clearly see a portion of the thin film progression in the area of the date. It's particularly cool when copper (or gold) has colors like that. But, you never see copper or gold with the typical A thru F toning that you get on silver (light gold centers, progressing to cobalt blue at the rims, classic album toning on silver). I think the first cycle colors are overwhelmed by the "color" of the copper, i.e. its absorptivity.

Silver is the ideal vehicle for this effect because of its near total reflectivity. Silver is "colorless" and works great as a coating for mirrors for this very reason. So in short, yes the same principles apply, but they are weakened and altered by the nature of copper.

drwstr123

Thanks for taking the time to discuss copper.
An excellent explanation.

lostincoins

Thank you very much for this information, it is very helpful.

WingedLiberty1957

A rare mint state Lincoln showing a broad Sunnywood spectrum ...

ms70

Extremely interesting but my head hurts now!

Just kidding! Great post and I'm not sure where or who else I could've ever learned all this from. Thank you!

ms70

Also, that backward holdered '58-D cent is really awesome. Not only the coin, but also having holdered like that!

DMWJR

Nice Lincoln!

Sunnywood

Nice job mapping the colors on the Lincoln, WL !!

OldIndianNutKase

Sunnywood,

I have always understood your explanation regarding the toning of silver and silver alloy coinage. I appreciate your opinion on and explanation of the toning on copper coins, of which I have a "few". I have had excellent success submitting RAW IHC prrofs that are toned. However, if I submit a RED IHC proof, it almost always is graded .91 (Questionable Color). Funny how a lot of blast white (silver) coins grade without any QC distinction that blast white is questionable for a coin over 100 years old. I guess that dipping silver is MA and dipping copper is not MA.

I do often question the authenticity of the toning on some of my slabbed IHC proofs. Some might even think that my avatar is .91........Toned copper seems to be a much more difficult call due to the inherent reactivity of copper vs. silver. And thank you again for your informed opinion.

OINK

DMWJR

Sunnywood, that 1882 looks like she is wearing sunglasses!!

wondercoin

Sunnywood... How many years do you estimate it takes to go naturally from W/X to terminal Y/Z?

Wondercoin

Nic

Love the chart Doug. I wish all coins toned with beautiful TFI. Many tone with little color at all.

Let's not ever call our superb classic blue grey coins terminal !

Sunnywood

OINK, I agree it's harder to get a handle on the colors on copper. And a lot of colorfully toned proof Indians started showing up at one point, which was obviously suspicious. I don't remember there being so many blue, red, pink and purple toned proof Indian cents years ago. So I invoke David Hall's comments about toned Peace dollars ... if they didn't exist years ago, they likely may be AT. Ditto for rainbow-toned nickels, especially Buffalo and Jefferson nickels.

I could pull out my mathematical model and try to adjust it for copper, taking into account the absorptivity of copper on certain wavelengths, which causes it to appear orange. Then I would also have to take into account the fact that copper oxides also have absorption properties, which is why copper goes brown relatively easily. But I have grown old and lazy, and I'm not sure I could work it out properly. Ah youth ... I used to be much sharper.

I also agree that dipped white coins are articial too. I used to call them "AW" - artifically white.

wondercoin, the rate of development of thin film oxidation / tarnish / toning varies greatly with the environmental conditions. I don't think it's possible to answer your question without a lot of data, and it would be a wide range depending on conditions. Under the kind of "good" conditions that produce great album toning (Benson, Newman, etc), it takes quite a while (otherwise all those coins would have been dull/terminal).

I have seen red pennies turn brown in days. And yet I have several gem full mint red large cents from tjhe 1840's and 1850's. It is not easy to explain or give a concise estimate !!! I have seen polished silver artifacts (my candlesticks, for example) run through first cycle colors and get to cobalt blue very quickly after polishing, and then the next time remain stable for weeks or months. There are a number of factors at work, including the chemist's notion of whether the surfaces are "active" or "passive." (Sorry I'm not really answering your question.)

Sunnywood

DMWJR

Sunnywood, that is where experience comes into play. Thanks for sharing yours!