Question about modern brilliant (mirror) vs cameo proofs.

[RWB]

I was reading Rick Tomaska’s book on Franklin halves last night, and a question about cameo vs brilliant proofs crossed my mind.

 

As Rick explained, a proof die was lightly etched in 5% nitric acid, then the fields (raised on the die) were buffed to a high polish. The inscriptions and portrait, being recessed on the die retained their etched surface. When struck on a polished planchet, the result was a mirrored field with frosty devices – a cameo proof.

 

During use, friction gradually smoothed the etched portions, resulting in less “frosting” on the devices, and less contrast between the fields and portrait/lettering. After a relatively small number of coins had been struck, the etched areas were completely obliterated, resulting in coins with a uniform mirror finish – the vast majority of all Franklin proofs.

 

My question is about the last part of this scenario. As etched metal is abraded and moved , the rough etched character would certainly be changed to something smoother. But it should produce something similar to a satin or even lustrous surface. How and why would it transform into a mirror similar to the polished fields? Were the blanks so highly polished that they transferred their mirrored surface to the formerly etched portions of the die? Were the dies simply polished all over after the initial use?

 

As an analogy, most agree that proof-like Morgan dollars result from polishing or lapping of a die. As the die is used the mirror gradually degrades into a smooth, and finally lustrous surface. That is, the surface moves from greater order (polished) to lesser order (smooth) – entropy.

 

For the modern proof coin description (above), it would seem that moving from etched (greater order) to smooth (lesser order) to mirror (greater order) violates basic physics.

 

Thoughts?

 

[James_OldeTowne]

Dies strike planchets, but you can also turn that around and say blank planchets are striking the dies. If you take an irregular piece of metal and continually pound on it with a flat piece of metal, what happens? The irregular piece will become flat as well. That's how I understand the process. The satin texture you mention does happen on the frosted devices, but only briefly, as it doesn't take long for it to be pounded to reflect the same mirrored texture as the blanks.

[WoodenJefferson]

There is no room for a novice collector as to how the proof dies of late 1948, 1950's and early 1960's would perform under curtain circumstances. There are certain things one must understand about the mechanics of a press capable of exerting 150+ tons onto an area no bigger than a poker chip. By simply walking across a floor, a 125 lb woman wearing spike heels can literally imprint a heel mark into linoleum floor. These are the tremendous forces at work here when dealing with high pressure presses, especially one designed to repeatedly imprint a design into a metal disk.

 

I fully understand your question and I seem to know more about what happens to the actual planchet as it is being struck than I do to the die part. It would seem to me that striking a planchet would be the same process as peening, the distinct process where the minute surfaces of the die would be compressed and hardened at the same time. The conicle (depressed) surfaces would become less and less distrupted as each impression were made with a resulting transformation of the devices taking on that same look as the fields.

 

We have some pretty smart cookies here that will and should shed a bit more sunlight on this intriguing question, I for one would like to know as well.

[RGT]

For the modern proof coin description (above), it would seem that moving from etched (greater order) to smooth (lesser order) to mirror (greater order) violates basic physics.

 

You didn't buy into all that nonsense about entropy, did you?

[physics-fan3.14]

For the modern proof coin description (above), it would seem that moving from etched (greater order) to smooth (lesser order) to mirror (greater order) violates basic physics.

 

You didn't buy into all that nonsense about entropy, did you?

 

I can talk physics with the best of them, but my metallurgy skills are somewhat lacking.

[cladking]

Dies strike planchets, but you can also turn that around and say blank planchets are striking the dies. If you take an irregular piece of metal and continually pound on it with a flat piece of metal, what happens? The irregular piece will become flat as well. That's how I understand the process. The satin texture you mention does happen on the frosted devices, but only briefly, as it doesn't take long for it to be pounded to reflect the same mirrored texture as the blanks.

 

The die should be sufficiently hard as to deform but spring back under the forces of coining. There likely is some permanent deformation from repeated stresses in the die and there certainly are in some cases. Most of the changes in the die, though, are from wear; the sloughing off of surface metal caused by the movement of metal in the planchets.

[Oldtrader3]

My understanding is that the dies are carburized, which would only be hardened to a surface depth of maybe 0.030 to 0.060. My guess is that they probably carburized the die surfaces to about Rockwell C-60/62 and then polished and acid etched the surfaces. The same as they do for injection molds.

 

The interior of the die still probably has a "sunshine anneal" (about Rockwell C-40/45 for air-hard, tool steel, bars). The acid etching is probably less than 0.001 deep. It appears that, even proof dies from the early fifties with only 50,000 or so proofs, have 10x more bright device (not polished) proof coins than etched surface coins. That would lead me to believe that the etching only lasted less than 5,000 coins, struck 3x each before they developed smooth surfaces on the devices. This is purely conjecture from experience as a tooling engineer many years ago.

[lehigh96]

I know I am new here but I am going to chime in anyway. Let me first state that I have a degree in metallurgy that I have not used in over 10 years. I graduated, worked for 1 year in the metals industry and changed fields for good.

 

I don't think that alloy used to make the die or even the hardness of the die are relevant to RWB's question. These two factors will only affect the overall performance of the die. If the die is not composed of a hard enough alloy, it will wear too quickly resulting in inadequate detail and strike, or worse the die would crack or break.

 

Instead, we should be focusing on what creates the cameo effect in the first place. The die is acid etched and then the surface of the die is polished. When the strike occurs, the polished planchet metal must still flow into the recesses of the die. This flow across the acid etched surface of the die causes the polished surface of the planchet to be disturbed yielding the frosted devices and the cameo effect. Over time, the wear on the acid etching reduces it's effectiveness to disturb the polished surface of the planchet. I guess the process would be like using a piece of sandpaper until it is no longer sandpaper, just paper.

 

Once this happens, there is no way for the die to disturb the polished surface of the planchet. The purpose of polishing the surface of the die is to remove the acid etching from the fields. It is not to impart a mirrored finish on the planchet. The planchet is already polished and already has a mirrored finish. In RWB's original question, he asked "Were the blanks so highly polished that they transferred their mirrored surface to the formerly etched portions of the die?" It isn't that the planchets affected the die, it is that the die no longer has the ability to affect the planchet.

 

Having said all that, I would like to say that I don't really collect proof coins, and I am certainly not an expert on the production process of proof coinage. If anyone has information that contradicts my theory, please let us know.

[RWB]

Very helpful. So the etched portion of the die would eventually abrade until its average surface matched that of the planchets…?

 

It also begs the question of whether the planchets were polished to as high a degree of mirror as the die fields. I cannot see any difference in mirror between the field and relief when I examine a common Franklin or other brilliant proof.

 

[physics-fan3.14]

Lehigh, you don't need to be afraid to chime in. We don't care how many posts you have, we only care that you have good information to contribute. Your post was very helpful and very informative, it makes perfect sense. Thanks.

[cladking]

I've long believed that degree of planchet polishing is the largest single component of what collectors refer to as "eye appeal". The mint does not vary any processes a great deal during the minting year usually but the texture of the metal used to cut blanks does vary more depending on numerous factors when it is rolled. Some coins have terrible surfaces simply because this metal is rough. The most dramatic example might be the 1942 aluminum coinage from one of the Yugoslavian countries. These can look attractive but luster is usually absent or very suppressed. Closer to home is the '69 quarter. These can often be lustrous enough but usually retain planchet scratches. "81-P quarters also have poor surfaces though some of this might be caused by die conditions.

 

Sometimes planchets can recieve a sort of partial polishing and these will often result in coins with booming luster or an undefinable "eye appeal". If a coin is gem in all regards and has this luster then it just looks better than comparable coins without it.

 

There are many ways that these special planchets get in the system. Usually it will just be a sheet that was smoother than most but proof planchets and other fully or partially polished planchets can get in the stream. I've always suspected that many of them are simply those which got caught up in the machinery and polished from bouncing around. They are usually too scarce for it to be a systemic "failure" and they come in a range and this implies that polishing was not intentional.

[rexcat]

There are a couple things going on during the stamping of proof coins that cause the die to fail to produce a frosty even finish to the devices. As mentioned earlier in this thread the planchet wears on the dies surface with every hit, this has the greatest effect on the highest points of the frosted area of the die face. Since these points on the die hit early (although it's the fields that contact first over all) they are in contact with the planchet fairly long forcing the flow of material against itself as it's driven into the coin's surface forming the lowest points in the devices. It's these spots on the coin that become glossy first, my 1883 proof quarter has just a few spots in the creases of liberty's robe like that on what is a very deep contrasting proof coin at first look. At the deepest points in the die the material is pushed into these areas die at the very end of the strike and the material barely makes contact much less be moving across it, this is the highest spots on a coins design which don't always get completely formed on business strikes, so proofs are hit several times to insure full detail of the design features.

 

Now the other thing that causes a lot of removal of the fine etching on the die's surface is the rouge cloth. With every hit on a planchet some of the coins material remains behind stuck to the die, what starts as a very small amount of material that couldn't be seen by the unaided eye can grow quickly into a problem like marks on the coin. So between coins the pressman would give each die half a little rub with a cloth that is embeded with extremely fine powder abrasive that can polish steel to a mirror. Or the die could be pulled and polished on the bench were some one could really go at it. Although it's most likely it was the mirrored fields that they wanted to stay smooth and flawless the same high points that are getting wear during use are also being touched with a polishing cloth which can remove the finish even quicker.

 

Although a polished planchet is needed to produce a deep watery mirror finish, the die surfaces must be polished to a mirror finish too. The fields of the coin get the watery mirrored finish from the die and any little piece of lint (which was common on proofs because of the cloth shedding during use) or oil, maybe even sweat leaves marks in the field, even the smallest marks stick out on mirrored fields.

 

During the 19th century it was common for the mint to put proof dies into service stamping business strikes when they were finished producing that years proofs, this could be were proof like coins come from, even without a specially perpared planchet these dies would produce better looking coins (for a while anyways) than a regularly perpared die.

 

 

[cladking]

 

During the 19th century it was common for the mint to put proof dies into service stamping business strikes when they were finished producing that years proofs, this could be were proof like coins come from, even without a specially perpared planchet these dies would produce better looking coins (for a while anyways) than a regularly perpared die.

 

 

There are several components of PL and not all PL coins share all of them. Perhaps the most noticeable at a glance is a booming luster but many basined dies produce highly PL coins without special luster. Solid strikes will sometimes produce square rims though this may be more of a modern phenomenon. Polished or overweight planchets and well executed dies can contribute. These are always VEDS as well.

 

The mint continued to use proof dies after they were retired right up to 1972 though they used only the reverse dies and, apparently, only some of them. SMS dies were proof dies and were extensively reused.

[WoodenJefferson]

SMS dies were proof dies and were extensively reused.

 

 

Cladking,

 

So you say the Special Mint Set were struck with proof dies? Were those dies the same standard as say 1964 and previous years? If so, was it the planchets in those SMS's that were not polished to a reflective surface then (cream of tarter, beads, etc.) to produce the Gem Proofs (cameo inclusive) we are accustomed to seeing in proof sets then?

 

~Wondering~

[cladking]

SMS dies were proof dies and were extensively reused.

 

 

Cladking,

 

So you say the Special Mint Set were struck with proof dies? Were those dies the same standard as say 1964 and previous years? If so, was it the planchets in those SMS's that were not polished to a reflective surface then (cream of tarter, beads, etc.) to produce the Gem Proofs (cameo inclusive) we are accustomed to seeing in proof sets then?

 

~Wondering~

 

Yes. Primarily.

 

The SMS coins were mostly struck only once as well. They used a few polished planchets and these seemed to have been uniform from one to the next.

 

There were probably some differences from previous years in die prep (there usually are), and there is more variability with the SMS dies, but they were essentially proof dies.

[RWB]

Proof coins from about 1860 through at least the 1960s were normally struck once on a medal press, not multiple times. Work hardening made the planchet too hard for a second blow to do much except mess up the 1st strike. (Once special presses capable of several very quick strikes became available in the 1970's some coins – mostly dollar-size commemoratives – did receive multiple strikes. 3 per ½ second was typical.)

 

MCMVII $20 were struck 3 times and annealed between blows. The EHR $20 were struck 7 times with annealing between strikes.

 

[Oldtrader3]

I did not make myself clear enough, I guess, but I was inferring that the striking of planchets by acid etched dies would wear the etched surface fairly fast through heat and friction of the planchet against the deeper die devices. This is evident by the small number of early proofs that have an etched surface transferred to the coin. I got off on the tooling tangent and did not explain myself well on the wear aspect. I assumed that the planchets were not highly polished by the lack of brilliance on the devices once the etching had worn off. Maybe I should not have bothered to post supposition on this subject at all. It just brought somewhat negative response.

[RWB]

All ideas are welcome - we have very little original source information on this subject. Speculation helps to focus discussion on several possible scenarios and that is very beneficial.