Featured What You Need to Know About: The Science of Toning

This coin has been in one of 1st Whitman coin view holder.all but this one stayed Gem Bu red.
Is this toning AT or NT

 

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I agree! but some coins no matter how airtight you have them will still tone,it may be the mix or metal.

I hate to see coin that have that pour on toner!:kewl:

 

The more I read about this the more ignorant I feel.

It's a common observation that after a coin has been dipped it will no longer tone attractively. What's the chemical/physical mechanism that makes the difference? Doesn't dipping remove flow lines and make the surface flatter, and if so why would that lead to gray toning instead of colorful interference?

The path length difference depends on the angle of incidence, unless my thinking is thoroughly confused. So shouldn't all toning be iridescent? If the geometry is independent of the angle of incidence, why is there iridescent toning at all?

 

IMO, it should read "has been OVERDIPPED it will no longer tone attractively." If a silver coin is going to be ATed, it will generally be dipped before the process begins. Otherwise the AT toning process could be uneven and spotty due to areas with thicker existing patina than other areas. When dipped first, the process can proceed evenly on the surface. AT is best on uncirculated or AU55+ coins that have not been over dipped, due to the flowed surfaces that remain.

If you are really interested in the toning process, read the links in this posting. It will take some effort and study, but you will have a good understanding of silver toning.


http://www.cointalk.com/t64441/#post657165




Jim

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Thank you for collecting those links: they do repay effort and study. I went and re-read them.

The discussions there address my questions, but still leave me curious. For example, Sunnywood explains why some toning depends on the view angle and other kinds don't by attributing the difference to whether the color comes from absorption in the chemical layer versus the thin-film interference effect which he and physics-fan have described for us. But if I understand right the interference effect is supposed to be the most important one typically, and it does depend on angle of view, so shouldn't most toning be iridescent?

Rob790 explains how work hardening affects reaction rates, and says that dipping chemicals inhibit natural toning. But how? There's also been a tantalizing reference to how different acid baths at the Mint correspond to different varieties of toning in the coins, which sounds like it might be the same phenomenon as the result of dipping (or overdipping as you point out). What is the key difference about an acid-washed surface that makes it tone differently?

(Am I going into more depth than anyone cares about? I don't mean to derail the discussion but really am curious.)

 

In the absorption model, imagine various photons bearing energy levels that produce various wavelengths of color hitting the surface( photons can be particles or waves. If the chemical structure of the silver sulfide or other toning agent causes the absorption ( incorporation into the chemical structure), then the remaining photons of different energy levels (color) can be reflected from the surface layer of the sulfide,oxide, whatever the toning agent is, so the apparent color will be all colors minus the color absorbed, angle of viewing would have limited effect on the tone color since the surface layer of the toning chemical would not have a "mirror" surface and the scattering would allow the similar proportions of remaining color to hit the retina and the brain interpret the same color.

When looking at photons as waves, we can see the wave actions where waves can cancel out, increase positive waveform or increase negative waveform, depening on how much out of phase the waveforms happen to be. The one reference shows how the phase is altered by the thickness of the thin film of toning material. This is how the different preceived ( by the eye/mind) colors are visualized. As the thickness increases, the phase difference doesn't just increase, it cycles ( + 0 - , + 0 -, etc) until the layer is so thick the reflectance is negated ( black end point). For one set of photons, the color would be very directional. However, the surface they are reflecting off is also not a "mirror" surface ( coin surface), so tilting the coin may direct other photons with similar phase difference into the eye and the same color in the same area.

This the understanding I have on the processes, maybe others can add or correct.

Jim

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If a person has had little background, they may find it interesting to take several coins with different toning colors and look at them under monochromatic light , such as only red light, only blue light , or only green light.

Jim

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I bet comic book collectors don't have anywhere near this much fun.

So have I got it right that when toning happens over an optically rough surface, such as the kind that makes a coin lustrous, the color that comes out is the result of multiple angles, just as the cartwheel effect on a lustrous coin is the sum of many different reflections? So that where a simplified model of a mirror-like corrosion layer over a mirror-like coin surface would tell you to expect iridescence, a more realistic one that takes scattering within the thin layer into account along with diffuse reflection from the coin surface tells you to expect colors that don't change with angle?

Does a proof start with polished dies and planchets? Does that mean there's less flow and fewer flow lines in the fields on a proof coin? Do proofs tone differently? Is that why Lehigh96 said that toned proofs were especially challenging to get good photographs of?

Thanks to everyone for their time! To put it in 1950's-compatible language, "Gosh, I sure like this place!"

 

Great Post

 

Well, I'm off to create some aratification toning yall....

 

You think the surfaces on an original toned coin are complex try a 200+ year old piece of furniture with untouched surfaces to sed chemical analysis of various layers is impressive I deal with both. Great theead!! Even tho some of the complex stuff beyond me. Not educated per say but got a tuned eye for subtle differences that can't always be explained

 

Beans!! A good old New England baked bean supper which i love. Makes me sound like a tuba player! Cabbage even worse!

 

LMAO @Mainebill ! The most volatile for me is White Castle sliders...WOHA!

All joking aside, I just finished reading this. Another fantastic write up by @physics-fan3.14 ...thanks!

 

Well, this is a bit of an ancient thread. Haha... last post was in late 2009.....

If y'all want a bit more on this topic, I have adapted this article into 2 chapters of my book (linked in my signature below)

 

This is very interesting. Throwback to AP Physics in high school! Sitting in class learning this, I though "I will never see this ever again once I am done with this class." I was right...until today.

 

Is silver sulfide the only type of compound that causes toning, or are there other chemicals that can naturally react with silver to form a patina?

 

Yes, there are definitely other compounds that can form toning. I mainly discuss silver sulfide because it is the most common - but basically, anything which will react with silver could potentially cause toning. The toning comes from the thin film interference - not from the film itself (so, the film could be anything). Copper also forms a very large number of compounds.

 

Since you actually mention eggs, I'll post here. I think we've all seen the ASE that has a rainbow, as a result of sitting in a box of matches. Well, here is an example of a bright, cleaned coin that was toned by sitting next to a hard-boiled egg, in a locked dish...



... next, we have a photo of a Morgan dollar, which resembled this fake toning with orangey spots on the head...



... it turned out to be just the lighting, as the coin is slabbed and graded MS 62...



... here is the slab...