What happens to a "woody" that is acid etched?

Ok, Ok, no games or tricks...

The surface of this coin has been etched. In the highest power images you can see how the different metals from the improper alloy mix (woody) are affected differently. Where the acid attacked the surface easily, the channels are deeper. Note that on the reverse there are fine raised lines caused by the same thing. Look at next post for images.

 

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Other images.

 

You do come up with interesting stuff.

 

Wow, you can see how the of grains have elongated during the rolling process.

 

Excuse an old teacher from asking ~ Where is the photo of it with the woody characteristics showing before the etching? Since the etching is theoretically producing grooves, so do many milling tools. Where is the direct correlation ?

 

Good point. Anyone who has the time to laser mill an Indian cent has too much time on their hands. He also forgot to recolor the piece back to brown with gold streaks rather than the pinkish-brown surface that does not "show" in my off-color balance image.

This is only the "after." I'm not the nutcase who ruined the coin; and I certainly will not ruin my beautiful woodies for a teaching demonstration!

 

It was etched.

Acid etching removes the surface microstructure and then begins to selectively remove the metal in the grains along crystal planes or compositional differences. That’s why the pics show grooves of different thicknesses and orientations. These are the structures of the original grains in the cast ingot. If the alloy was homogeneous, then the etching on the various grains would be similar in appearance.

Although the coin is ruined, this is a great example showing the how different metal grains look after improper mixing. It's a topographic representation of the toning seen on "woodies". You can even see the direction that the strip was rolled, since the grains are stretched during this process.

 

I admit, it appears etched. But direct correlation to a previous 'woody' pattern of the etching is needed evidence of the link of cause and effect. I think insider produced excellent photos of the etching.
Although my metallurgy is limited, you say:

But the cast ingot is multiples of thickness to the planchet which I assume is flattened to size by rollers, and then punched out. Since rolling would cause lateral as well as vertical movement of the grains wouldn't most coins shows at least some of similar variations of the grains? Press pressure on the planchet I don't know, just asking as to understand and gain knowledge.

I agree bad mixing could be the cause, it was always assumed to be, but to my knowledge never acknowledge by the mint or experimentation. Insider, any deeper sources? Jim

 

I have enjoyed this thread more than any thread Insider has ever started.

 

@desertgem

No, Improper alloy mix is what I was told by many sources including those at the Philly Mint. See images at the bottom of this post. That's the type of crystallization I like better than woodies. I was told this is a similar thing as the different metals separated during cooling.

@Oldhoopster posted: "Although the coin is ruined, this is a great example showing the how different metal grains look after improper mixing. It's a
topographic representation of the toning seen on "woodies". You can even see the direction that the strip was rolled, since the grains are stretched during this process."

I was waiting for a member to ask which direction the strip was stretched as I never gave that a thought in the past. Hopefully, Oldhoopster will educate us.

@mikenoodle Thanks, I'm trying to play nice. I have hundreds of images to post; but this is not as much fun as the way I was taught by being asked "What happened to this coin!" Then each of our incorrect guesses were explained away until we got the answer.

 

It looks more like granite than it does bronze. I would guess that the different alloys must have cooled at different temperatures to create such a striated metal.

 

I'm not a metallurgist either but here is my reasoning. As the melt in the ingot cools, improperly/incompletely mixed regions crystallize with diff compositions in diff regions (I think uneven or incomplete heating could be as just as likely as improper mixing). The flattening and stretching during rolling should distribute some of these grains near the surface since the strip has more surface area than an ingot. If the acid attacks the varying alloys in the grains differently, it would result in different patterns for each compositions.

On coins with a homogeneous alloy, I would expect etching within the grains to be similar, since each has the same composition. I think there was a post a few weeks ago where someone showed a cent that was dipped in acid. It showed ridges and ripples as well but not the distinct orientation as seen on this coin.
I'm comfortable with the logic, but would love to here from someone with a metallurgy background to tell me what I'm missing

 

The ingot was rolled between the 1-2 O'clock position and 7-8 O'clock position (I believe they roll in both directions). During rolling, the ingot gets flatter and longer but not significantly wider, so any metal grains with diff alloys are going to be stretched. On your coin the areas of that are show a similar etching patterns are elongated along this axis.

Assuming the science is correct (not a given, but I think it sounds good), I believe you can make the same inferences regarding the toning regions on woody coins as well.

 

Oldhoopster, posted: "The ingot was rolled between the 1-2 O'clock position and 7-8 O'clock position (I believe they roll in both directions). During rolling, the ingot gets flatter and longer but not significantly wider, so any metal grains with diff alloys are going to be stretched. On your coin the areas of that are show a similar etching patterns are elongated along this axis."

The strip is only rolled in one direction. I'll need to find out about stretching patterns because we know the strip is stretched out as it is made thinner.

 

When I said both directions, I meant back and forth only. As the strip gets longer, it's a lot easier to close the roller and push it back through than it is to carry it back around to the other side of the machine

 

On a large scale, wouldn't it be best just to have a line of roller machines, the number of which are the number of operations necessary to get to the desired thickness? ...just seems like that would be the optimal way to do things with less unnecessary movement of material and time down for adjustments.

...and that '77 looks like somebody drew on it with a pencil. ;p