question for morgan (or toning) experts

AceK

I received today a nicely golden toned 1886 morgan I picked up on ebay and am perplexed by what look to be untoned areas underneath the date which give it almost a doubled appearance. Here's a closeup of the date:



And just for the heck of it, here's a full picture:



I'd be most curious if anyone can tell me what's going on here.

Leiana

I've seen that before. It is a result of the raised devices keeping the toning substrate from touching the entire coin.

-Amanda

MrSpud

I've read that that is an indication of NT. For quickly made AT, the color often runs right over from the fields to the devices. Something about the difference in density of the metal right next to the devices causing a difference in thin interference film formation or something like that.

AceK

<< <i> I've read that that is an indication of NT. >>

But it's in a PCGS slab, so we KNOW it couldn't be AT . . . .

LincolnCentMan

That's normal for NT coins. It's caused from stresses in the metal during the striking process. It makes those areas less likely to tone because of the flow stress on the metal there.

David

p8nt

<< <i>I've seen that before. It is a result of the raised devices keeping the toning substrate from touching the entire coin.

-Amanda >>



I respectfully disagree. The 'toning substrate' you speak of would not touch north, east, and west of the digits but not south.



<< <i>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. >>



Above is another board member's writing on the subject.

Leiana

<< <i>

<< <i>I've seen that before. It is a result of the raised devices keeping the toning substrate from touching the entire coin.

-Amanda >>



I respectfully disagree. The 'toning substrate' you speak of would not touch north, east, and west of the digits but not south.



<< <i>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. >>



Above is another board member's writing on the subject. >>




Well, I respectfully thank you! I learned something new.

-Amanda

AceK

So it's altered metallic structure caused by die pressure. Most interesting. I certainly never would have guessed that one. Thanks everyone for your help!

Myqqy

Above is another board member's writing on the subject.

Was that TomB who wrote that, or someone else? I remember reading that, but cannot remember who originally wrote it...

airplanenut

<< <i>So it's altered metallic structure caused by die pressure. Most interesting. I certainly never would have guessed that one. Thanks everyone for your help! >>

Look at the metal right next to the date closely--it should look a bit off from the rest of the fields. You can also see this on white pieces, and I've seen some very good examples on 1886 dated pieces.

airplanenut

And here's a very good example of the effect:

p8nt

<< <i>Above is another board member's writing on the subject.

Was that TomB who wrote that, or someone else? I remember reading that, but cannot remember who originally wrote it... >>




I don't remember either or I would have credited them for it I have the post saved on my computer in a Word doc so I don't know who wrote it.

AceK

<< <i>Look at the metal right next to the date closely--it should look a bit off from the rest of the fields. >>

You are absolutely right. The toning around the devices is different all the way around the obverse. And several of the stars also exhibit the same "white shadow" effect as the date.

Some people look at this morgan, all they see is an old coin; I love how here it can become an object of endless fascination and study.

morgannut2

The above toning disussions are mostly right---I'm WAY TOO TRIED explain (again) the various forms of cubic packing, cubic-closest packing, and unusual cupper alloy moloecular structures, that often form, then impact and affect thin-film color interefance spectrums.
Think of it this way------How Much does the toning and "color" of fresh ice change in it's look, on a rink asa the a ice skating surface looks/wears-away as time passes.?? (That color is thin film interference too-- just a diffeent nomal reactive chemical bound)

-----That's a stupid and simple answer why this happens---in especially date areas---and why it means nothing.

ibzman350

I like to call it the shadow effect







BTW........ neat die chips.


Herb