Colors of US gold coins 1 1

[GoldFinger1969]

43 minutes ago, VKurtB said:

Then ‘splain to me why Doug insists that mirrored proofs have full luster. Mirrors don’t DO luster. 

Could be because of the relationship between mirrored fields and luster.....maybe mirrors have no luster or perfect luster....or both......sort of like what is the weight and size of a singularity at the center of a Black Hole.

Or....how many licks does it take to get to the center of a Tootsie Roll Pop.

The world may never know...... 

 

 

[VKurtB]

3 minutes ago, GoldFinger1969 said:

Could be because of the relationship between mirrored fields and luster.....maybe mirrors have no luster or perfect luster....or both......sort of like what is the weight and size of a singularity at the center of a Black Hole.

Or....how many licks does it take to get to the center of a Tootsie Roll Pop.

The world may never know...... 

 

 

If luster is due to /\/\/\/\/\/\ , and it IS, then mirrored fields have no luster. They surely do have perfect SOMETHING, but it ain’t luster. 

Edited June 23, 2021 by VKurtB

[RWB]

It's the kind of sloppy language that eventually causes problems.  A deep mirror proof coin has almost no luster (caused by repetitive surface irregularities) in polished areas.

The smoothest coin surface is mirror-like, as the proportion of irregularities increase, the surface becomes less mirror-like. This is the result of greater scatter of light by roughness.

[GoldFinger1969]

44 minutes ago, RWB said:

It's the kind of sloppy language that eventually causes problems.  A deep mirror proof coin has almost no luster (caused by repetitive surface irregularities) in polished areas.  The smoothest coin surface is mirror-like, as the proportion of irregularities increase, the surface becomes less mirror-like. This is the result of greater scatter of light by roughness.

I think some people -- I used to be one before I read your book -- confuse scatter of light with reflectivity.  

That 1908-S really has nice scatter and color but it is clearly not a mirrored coin or proof.

[lehigh96]

15 hours ago, GoldFinger1969 said:

So what do you think causes the differences between those 1908-S's I posted above....and a pretty bland 1924 Saint ?

The toning on the 1908-S is what you would typically see on a gold coin where the color starts to change from bright gold to more of an orange gold.  The rainbow toned 1924 is something else entirely, and despite Roger's insistence to the contrary, it is believed that improper alloy mixture where the concentration of copper is higher at the surface allows for the dramatic toning.  I checked the phase diagram for AU-CU and it says that gold forms a solid solution with copper at all concentrations at most temperatures, which indicates to me that the culprit would be diffusion of the copper atoms towards the surface.  I have a degree in metallurgy that I haven't used in many years, but it should seem reasonable to everyone that it is the copper in the alloy that is the driving force behind the toning on gold coins in the absence of impurities.

[lehigh96]

11 hours ago, VKurtB said:

Then ‘splain to me why Doug insists that mirrored proofs have full luster. Mirrors don’t DO luster. 

Well, like you, I don't even think of luster when talking about proof coins, so I will amend my statement to say that Doug's understanding of luster on "business strike" coins is correct.  That said, he is wrong so often that this falls under the category of "a broken clock is correct twice a day."

[VKurtB]

1 minute ago, lehigh96 said:

Well, like you, I don't even think of luster when talking about proof coins, so I will amend my statement to say that Doug's understanding of luster on "business strike" coins is correct.  That said, he is wrong so often that this falls under the category of "a broken clock is correct twice a day."

Yup, this’ll happen to a guy who intentionally stopped learning anything some 35 years ago.

[lehigh96]

Just now, VKurtB said:

Yup, this’ll happen to a guy who intentionally stopped learning anything some 35 years ago.

Posts like this are why I miss you over there.  That said, he is not the omnipresent slinger of misinformation that he once was.

[VKurtB]

Just now, lehigh96 said:

Posts like this are why I miss you over there.  That said, he is not the omnipresent slinger of misinformation that he once was.

But he still insists on defining words his own way so that he’s “never wrong”, substantively or procedurally. 

[GoldFinger1969]

54 minutes ago, lehigh96 said:

The toning on the 1908-S is what you would typically see on a gold coin where the color starts to change from bright gold to more of an orange gold.  The rainbow toned 1924 is something else entirely, and despite Roger's insistence to the contrary, it is believed that improper alloy mixture where the concentration of copper is higher at the surface allows for the dramatic toning.  I checked the phase diagram for AU-CU and it says that gold forms a solid solution with copper at all concentrations at most temperatures, which indicates to me that the culprit would be diffusion of the copper atoms towards the surface.  I have a degree in metallurgy that I haven't used in many years, but it should seem reasonable to everyone that it is the copper in the alloy that is the driving force behind the toning on gold coins in the absence of impurities.

Very interesting....I always wondered how they made sure the 90/10 alloy was properly "mixed" so as not to have a concentration of copper in one area of the coin, like at the top.

The UHRs have that special gold sheen look on the obverse because of the annealing procedure.  So pure gold on the surface has its strengths in addition to copper doing the toning bit.

[RWB]

8 hours ago, lehigh96 said:

despite Roger's insistence to the contrary, it is believed that improper alloy mixture where the concentration of copper is higher at the surface allows for the dramatic toning

This is simply false. The "same cadre of experts" has been wrong about many important coin characteristics and processes. It assumes conditions that did not exist and a result that would condemn nearly every gold ingot.

8 hours ago, lehigh96 said:

...gold forms a solid solution with copper at all concentrations at most temperatures, which indicates to me that the culprit would be diffusion of the copper atoms towards the surface.

"Solid solution" is correct and "diffusion of copper" in incorrect, which demonstrate why the "improper alloy mixture" is wrong for gold-copper alloys.

In a solid solution the minor component is uniformly mixed within the major component crystal lattice. This explains why at the Mint gold and copper were readily combined into a "solid solution" that did not segregate on solidification. This was tested many times at Philadelphia, Bureau of Standards (now NIST), Royal Mint, etc. Copper can be depleted or altered from a gold coin's surface by repeated dipping in acid (HCl, H2SO4, etc.) --refer to MCMVII Ex High Relief DE patterns-- but it cannot be augmented. It does not "diffuse towards the surface" of an ingot, strip, blank, planchet, or coin. Any gold coin toning is a surface compound film byproduct, or aggregated contamination (dirt, rust, salt erosion, oil, and so forth).

However, silver and copper do not form an entirely uniform solid solution - they form intermittent crystal bonds, that is, silver aggregates at copper grain boundaries - and thus the material will segregate on solidification. The degree of this is easily measured in manufacturing situations. The US Mint M&R had a target assay of silver ingots that was below tolerance, then the Coiner cut blanks from the center of each strip, producing blanks that were very close to 0.900. The scrap, low fineness, was sent back to M&R where it was used as the base for the next melt batch. (As an aside -- This is one of the technical reasons the Charlotte and Dahlonega Mints were never allowed to strike silver coins - getting and keeping 0.900 fine silver coinage strip was difficult.)

Thus, silver coins are more likely to have alloy differences if cut from parts of the strip with excess segregation. Also, copper, tin and zinc are conceptually more like a solution - solvent and solute - where producing a reasonably uniform ingot depends on critical temperature control during melting. (Think of the difference between dropping a raw egg into lightly simmering water and into rapidly boiling water....The first produces a perfect poached egg; the second created strings and threads of egg white and a tough yolk.)

Maybe the "improper alloy mixture" is one of those old wives' tales that got extrapolated from a correct situation to one that was incorrect.

Edited June 24, 2021 by RWB

[RWB]

3 hours ago, GoldFinger1969 said:

The UHRs have that special gold sheen look on the obverse because of the annealing procedure.  So pure gold on the surface has its strengths in addition to copper doing the toning bit

This is a product of acid dipping the incomplete coins after each annealing. It is also present, but to a minimal extent on MCMVII circulation DE.

[Henri Charriere]

16 hours ago, VKurtB said:

Then ‘splain to me why Doug insists that mirrored proofs have full luster. Mirrors don’t DO luster. 

Hmm, I am beginning to think Original Mint Luster is one thing and Mirrored Proofs with full luster is quite another, and the terms should not be used interchangeably.  

[RWB]

54 minutes ago, Quintus Arrius said:

Hmm, I am beginning to think Original Mint Luster is one thing and Mirrored Proofs with full luster is quite another, and the terms should not be used interchangeably.  

An "original surface" can be anything, but can usually be described very simply. Problems occur when people get overly enthusiastic (or greedy), and start mixing words of conflicting meaning in the same description. The obvious example is that a "mirror proof" cannot also have "luster" - BUT the mirror on a proof coin varies with the smoothness of polish, so a "mirror proof" might actually have a little luster created was the die surface changes during use. In the original example, a conflict was created by juxtaposing conflicting terms "mirror" and "luster."

[RWB]

For many, I am being "too picky" and likely overly dogmatic. I'm used to hearing those complaints from my very first published article right up to yesterday afternoon. That's OK.

[GoldFinger1969]

19 minutes ago, RWB said:

For many, I am being "too picky" and likely overly dogmatic. I'm used to hearing those complaints from my very first published article right up to yesterday afternoon. That's OK.

Not at all, I like the back-and-forth that's how I learn.  

Look....no 2 coins from the same type let alone year and mintmark look exactly alike.....there are differences in the metal given to each on the surface and sub-atomic level....the strike and press of the old coin presses....etc. 

Things got worn over time 100 years ago that today don't happen and if something is off by 0.000001% today, an alarm goes off.  Back then, they kept striking and minting until something broke and it stopped.

 

[VKurtB]

42 minutes ago, RWB said:

I am being "too picky" and likely overly dogmatic

I prefer manual transmission dogs.