Do you agree with David Lange’s theory on hard/soft planchets, and the effect on toning?

Longacre · July 29, 2007 10:55PM

I was reading the recent QDB article in Coin World about Lincoln cents. The article dealt with sharp and weak strikes, and toning on cents. QDB referenced a theory that David Lange developed to explain the relationship of toning to strike on Lincolns. Here is a quote from the article,

“It seems that planchets that were soft produced very sharp coins, provided that the dies were not worn and were spaced properly in the press. However, the softness seems to have made the coins especially susceptible to toning quickly. Hard planchets produced coins with weakly defined details, but that were apt to remain brilliant for a long time.”

I did not know that there was any relationship between the hardness and softness of the planchets, and the toning of coins. Do you agree with this theory? I thought that toning was a physical/chemical reaction with the metal itself, and the fact that the planchet was hard or soft should have no bearing on whether the coin tones quickly or not. Or does the toning reaction become “easier” with a softer planchet versus a harder planchet?

curly · July 29, 2007 11:10PM

Brother, that's some pretty deep thinkin' for an old country boy like me. I agree with you though, I don't see what the hardness of the planchet has to do with it. Besides, what is considered a hard planchet? When is a planchet considered soft?

Lord, my head hurts already, I'm goin' back to bed.

Gemineye · July 29, 2007 11:11PM

I would think it would....

<< <i>annealing
The heating of a die or planchet to soften the metal before preparation of the die or striking of the coin. >>

This is taken from PCGS definitions and it woud be a great factor in the process of later toning.

jabba · July 29, 2007 11:23PM

Sounds good to me,

MrEureka · July 29, 2007 11:25PM

I suspect that Dave is on the right track, but for the wrong reason. My guess is that the variance on toning is based more on the way that metal flows and is actually stretched when the coin is struck. I say that because I think of the toning shadows you sometimes see around the outer edges of stars and letters, especially on coins struck out of collar or in a loose collar. The change in surface texture (i.e., metal flow) leads to a change in the way the coin tones.

Edited to add that I would expect the metal flow to be more consistent on a coin struck on a soft planchet.

CaptHenway · July 29, 2007 11:37PM

Interesting theory that I had never considered.

Another thought: Coins heat up under the pressure of striking. I wonder if coins that are well struck due to high pressure heat up more, and this affects the subsequent toning?

TD

MrEureka · July 29, 2007 11:40PM

I wonder if coins that are well struck due to high pressure heat up more, and this affects the subsequent toning?

It would be interesting to compare the toning of proofs and uncs put away in the year of issue, and stored together since. Would the uncs be more toned?

ricko · July 30, 2007 12:00AM

The degree of hardness would certainly be relevant to the annealing process, but also to variations in the metallurgical composition of the planchet. As TD mentioned, the striking pressure (die spacing) could also affect the surface condition. All processes have tolerances... given that, the variances between the two extremes would definitely contribute to degree, speed and resulting phenomena of toning. Cheers, RickO

gyocomgd · July 30, 2007 12:02AM

Mike, you're running out of things to think about. Start reading a good book.

Harder metal means denser metal. The molecules are spaced closer together. When they're spaced farther apart, oxidization can creep into the metal better.
That's my theory, and I'm sticking to it.

eyoung429 · July 30, 2007 12:12AM

I would have to agree with gyocomgd's assesment. A hard planchet would have less "pockets of air" for cohesion of oxidation. Whereas a softer planchet would accumulate dirt, oils and oxidation. This would also explain why a "dipped" coin would tone differently and more quickly. If you remove the contaminants from the coins surface, you would increase the surfaces that the oxidation would be able to adhere to.

Think of it as having a hole in a piece of fabric, if you remove the hole....it only gets larger.

Barry · July 30, 2007 12:27AM

Thinking back to my Materials classes in Engineering school, it makes some sense. The hardness of an alloy or metal is related to its crystalline structure. If the bonds are stronger, it may be less susceptible to oxidation, i.e. toning.

CaptHenway · July 30, 2007 4:46AM

Just to clarify a point, I am pretty sure that David Lange was talking about the relative hardness of one batch of planchets compared to another, due to variables such as work hardening during rolling and annealing after upsetting, and not due to any significant difference in the alloy.

When the Mint first started using the 75% copper/ 25% nickel alloy in 1865, they had a wide allowable variance in the alloy, so that one batch might have significantly more nickel in it than another. However, most U.S. coins are very standard in their alloying, which should not affect the striking.

TD

halfhunter · July 30, 2007 5:20AM

It would be interesting to compare the toning of proofs and uncs put away in the year of issue, and stored together since. Would the uncs be more toned?

This is certainly not scientific, but about a month ago I got bored and put an UNC & a Proof '82 GW Commem into a Wayte Raymond page and stuck them in the attic.

If anyone is interested, I will post which starts to tone first and/or tones fastest.

Best Regards,

John

eyoung429 · July 30, 2007 5:54AM

I can understand that...albeit the composition is not going to change the amount of oxidation or accumulation of foriegn substances. I was agreeing upon the timeline that the process would occur.

cladking · July 30, 2007 6:18AM

There are a lot of factors and what's true for one coin might not be true for another.

Toning has a great deal to do with surface conditions since most toning is related to
contaminants or chemical processes on the surface. There is less variation after strike
between the hardness of coins than before.

Smoother surfaces tend to produce more vibrant toning. Coins that are weakly struck
for any reason are less likely to have a lot of toning.

EagleEye · July 30, 2007 6:39AM

I think the toning will also vary due to the way the Mint washed the planchets. That should not vary in the same group of planchets though, more like series wide, like toning on 1916-1933 silver coins compared to earlier and later years.

Nysoto · July 30, 2007 6:49AM

If a planchet is incompletely annealed (less soft), vrs a planchet that is appropriately annealed (very soft), wouldn't the work hardening from the tons of pressure of the strike equal out the hardness of the two planchets? A proof coin with multiple strikes under greater pressure should have greater hardness (this would be an interesting experiment with a Brinnel or Rockwell hardness test).

I have anealed sterling and copper thousands of times with a silversmithing hobby/business, and have not noticed any difference in toning/patination from areas that were extremely work hardened next to completely annealed areas on unfinished projects and metal scraps that sat for years. I did notice differences in toning from different surface textures and finishes (satin vrs mirror). The largest difference is from residual flux and pickling agents that were not completely washed off the metal.

I would be interested in knowing the process the US Mint uses (and used at different time frames) for annealing, if air, water, or other quenching was used, and what type of liquid was used to pickle/wash the annealed planchets, which can effect the toning. Some of the Franklin toning appears to be unrinsed liquids that affected the coin, the splotchy reddish brown toning is found on some of my sterling, if not washed off.

RWB · July 30, 2007 6:57AM

After annealing (softening by heat treatment) planchets were cleaned and dried, then delivered to the press room for coining. Softer planchets might have taken a better impression from the dies than a harder planchet. However, differences in chemical reactions involving the coin's surface would not have begun until after the coin was struck. At that point, a well struck coin – preserving all the fine detail of the dies, might have presented a greater surface area than a poorly struck piece where the fine detail was smoothed. (Think particularly of the bison on a Buffalo nickel. Compare the roughly textured area on and above the front legs – on a poorly struck piece, this can be soft and almost smooth.)

The increased surface area would present more reactive metal, and thus tone more quickly than a weakly stuck piece.

Would someone volunteer to ask Director Moy to run a few experiments when he gets back to the shop? Also ask him about “milk spots.”

Do you agree with David Lange’s theory on hard/soft planchets, and the effect on toning?

Comments

Leave a Comment