What is Luster?

[CarlWohlforth]

I thought I knew what luster was.

 

I've been told luster is from metal flowing out from the center when struck by a die. You can see it on coins by looking for the cartwheel effect. When you tilt a Morgan under a light the reflected light rotates around the coin. My daughter sees it and says it looks like a bow tie, she calls it the bow tie effect.

 

Now I don't see that effect on modern DCAM proof coins. I really don't see it on most proofs. I don't see that effect on DMPL Morgans either. If they have some cartwheel effect they might be plain PL, not PL at all if they have the full effect. I thought these coins didn't have any or much luster because the planchets were polished and the dies new which minimized the flow of metal.

 

So what am I missing? Can a DMPL Morgan have luster? If a DCAM proof can have luster what does it look like compared to a DCAM proof with poor luster?

[carterhaines-migration]

This cartwheel effect that you keep quoting is only one way to check for large amounts of luster. Luster is simply what causes the shine on a coin; it acts as something to help light reflect off the metal. The cartwheel effect is seen because of the way the light reflects off the coin/luster as you tilt the coin. The cartwheel effect is actually a quite stupid thing as a polished coin (polishing is basically adding luster) will have a much better cartwheel effect, but also a much lower value.

[MarkFeld]

Carl, you're doing just fine. Luster can be defined simply as "the glow of reflected light".

 

When writing descriptions of coins for our web site, I don't typically refer to the luster of a proof coin as I would that of a business strike. However, technically speaking, proof coins do have luster, too. It's just that it has a different look, due to the way the light interacts with the reflective, mirror-like surfaces.

[msmhappy]

Well stated carter!! I cant add anything to that....

 

mike

 

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dont forget! collect proof sets!!!!!!!!!!!!

[shylock]

I guess luster can be a very general term used on any type of coin, but I think of it as an MS trait. The metal flow you mentioned is what provides the texture that reflects light in different directions, the cartwheel effect I think of as luster. Proofs (and prooflike MS coins) have the type of surfaces that reflect light in only one direction and "luster" doesn't describe that as well to me as just plain "mirrors".

[CarlWohlforth]

I have been thinking much along the lines as Shylock.

 

Now I hear the term "flashy". I thought that might be a good term to use for a bright, highly reflective coin, that doesn't show much luster. What does that term "flashy" mean to you?

 

What about a toned coin? The surfaces might have that flow lines effect but it won't reflect light well...

 

 

[Higashiyama]

Carterhaines --

 

I don't think the luster on a polished coin is likely to cartwheel. The polishing will remove the flow lines, and light will reflect in any direction, so the cartwheel is eliminated. Overdipping can also eliminate a cartwheel.

[cladking]

Luster is an effect left by the action of the dies. When the dies impact and compress the planchet with pressure which can exceed one hundred ton per square inch the metal will act much like a liquid and flow into the recesses of the die and toward the parts of the coin which is thickest. This flow tends to be greatest near the surface of the coin between the fields and the higher features or rim. It appears as though the luster actually has some depth and has a greater density and/or hardness than the rest of the coin. The luster can be abraded lightly for some time before it losses it reflectivity (is broken). Proof coins normally wouldn't show the cartwheel effect because the fields are flat and before they get any character from the wear caused by metal flow they are swapped out. Fields on unc coins are not normally flat and most do show some die wear.

[true_grade]

From the ANA:

 

"When a die pair strikes a coin, the metal of the planchet expands radially (from the center of the die outward in all directions). This expansion, with repeated strikings, will begin to erode the die and cause microscopic flow lines in the die's surfaces. These flow lines are in turn, transferred to every coin subsequently struck by those dies. It is the interaction of light with these minute peaks and valleys on the coin's surface that creates the fresh, usually lustrous appearance of uncirculated coins."

 

"The third category of luster is prooflike, in which a coin's finish is similar to that of a Proof coin. Its fields are highly reflective, which is caused by polishing the dies. The lowest part of a coin is its field, and a die is the opposite, or negative image, of what is seen on the coin. As the highest points on the die, the fields are the easiest areas to polish and, consequently, are the die's most reflective areas. Dies are primarily polished to remove the effects of die erosion and extend die life."

 

The dies for Proof coins are handled and cared for with extreme predjudice, thus comparing the luster on a business strike with Proof strike is not the same.

 

Does that help?

 

[Leothelion]

Hi Carl Great thread!

This will, in effect, tip the scales on how much I really know about coins. What's the difference between the brilliance and the luster of a coin? I have generally thought that one was stationary (in or on the coin's surface) while the latter was active, the reflection of a light source off the coin into your eyes. Because of the numerous angles a coin may have and because we can see only a very small proportion of the surrounding light that bounces off everything or the coin, We only see that small emittance of light that has arrived to the eye from that 1% of the multiple of angles available to us. Otherwise we would be blind as a bat if we were able to do so. How's that reasoning for your comtemplation.

 

Leo

[greghansen-migration]

"a polished coin (polishing is basically adding luster) will have a much better cartwheel effect"

 

Boy, I have to disagree with that comment pretty strongly. Very much contrary to my experience. Polishing may increase the overall 'reflectiveness' of the coin but it certainly won't give it a better cartwheel effect...it will in fact diminish if not totally eliminate it. The flow lines are abraided, flattened and otherwise smoothed out so that the polished coin has a much more overall reflectiveness when held under a light source.

[true_grade]

"a polished coin (polishing is basically adding luster) will have a much better cartwheel effect"

 

Boy, I have to disagree with that comment pretty strongly. Very much contrary to my experience. Polishing may increase the overall 'reflectiveness' of the coin but it certainly won't give it a better cartwheel effect...it will in fact diminish if not totally eliminate it. The flow lines are abraided, flattened and otherwise smoothed out so that the polished coin has a much more overall reflectiveness when held under a light source.

 

Yuz be right!!

 

A polished coin is like spit shining your black leather boots and using a baby diaper to put a mirror finish to it.

 

Luster is basically the reflection of light off of a "pattern" in the coins metal, not a mirrored reflection.

[GDJMSP]

From the ANA:

 

"When a die pair strikes a coin, the metal of the planchet expands radially (from the center of the die outward in all directions).

 

Maybe I'm being picky - but I've always had a problem with that statement.

 

When a planchet is made - it is flat and has consistent thickness. A die on the other hand is not of course. But where is the deepest section of the die ? In the main devices - usually the center of the coin. ( now I know this is not true for every single coin design - but it is for most of them )

 

So when the dies strike the flat planchet - the metal actually flows to the deepest part of the die - the center. So the metal flows inward - not outward.

 

The concept is valid regardless - but it is the ANA - a group who should know better. They really need to correct that statement on their site. If they are going to teach - at least do it correctly.

[BankNote1]

I could be wrong but a blank planchet isn't flat, it is sort of bowl shaped. It is also has a smaller diameter, and thicker than the struck coin. There has got to be some outward flow. I have never heard of the flow being inward! I don't think that is possible?! IMO.

[cladking]

A type 1 planchet is essentially flat, but does have a little bit of a bowl shape. The planchet is "upset" (forced between two rollers to reduce it's diameter) to increase it's thickness at the edges and help raise a rim on the finished coin. This is a type 2 planchet. Stuck coins are usually much more bowl shaped (depending on design) Metal moves throughout the planchet during the strike. There tends to be more movement outward on the surface of the coin though since it's diameter in being increased. Adjacent to major design features there can be inward flow, especialy nearer the center of the coin.

[Leothelion]

From the ANA:

 

"The third category of luster is prooflike, in which a coin's finish is similar to that of a Proof coin. Its fields are highly reflective, which is caused by polishing the dies. The lowest part of a coin is its field, and a die is the opposite, or negative image, of what is seen on the coin. As the highest points on the die, the fields are the easiest areas to polish and, consequently, are the die's most reflective areas. Dies are primarily polished to remove the effects of die erosion and extend die life."

 

The dies for Proof coins are handled and cared for with extreme predjudice, thus comparing the luster on a business strike with Proof strike is not the same.

 

Does that help?

 

I was JOKING in my last post. So now I'm very serious when I ask, why can't a prooflike coin be the results of a overpolished area on the roll sheet of coin metal before it was punched out into a planchet or proof material that was roughed up to be used for business strikes? But I do agree with the polishing of the dies that result in a prooflike coin because I have several with those charatoristics.

The lines seem to always run horizontal. I'll try to post a pic this evening.

 

Leo

[true_grade]

why can't a prooflike coin be the results of a overpolished area on the roll sheet of coin metal before it was punched out into a planchet or proof material that was roughed up to be used for business strikes?

 

Only planchet "problem" I am aware of would be from poor alloy mixtures.

 

I don't belive the planchets are polished; a coil is rinsed and wire brushed; the planchets are cleaned in a "hot soapy bath" after annealing, but to my knowledge, no polishing takes place

[true_grade]

So when the dies strike the flat planchet - the metal actually flows to the deepest part of the die - the center. So the metal flows inward - not outward.

 

I think I see what you're saying.

 

The metal is only "flowing" due to pressure, not liquidity.

 

The metal would "flow" away from the greatest pressure instead of gravity pulling it to a low point.

 

[cladking]

Coinage strip is never intentionally polished. If it is to be used for proof coins then the planchets are cut and upset and then polished. Coinage strip does vary in quality. There can be some which is much smoother than others, but probably none which approaches polished. Individual planchets however can become polished inadvertantly if stuck in the machinery or prepared for proof strikes and then used elsewhere. Such coins are rarely seen but there are business strikes on polished planchets.

 

Sometimes there is experimentation with polishing planchets also. Many of the SMS coins were struck on polished planchets.

[Hoot]

Many of the SMS coins were struck on polished planchets.

 

Was it many or all of the SMS coins? These remain a bit enigmatic to me. Also, many of the business strikes, particularly the Jefferson nickels, from 65-67 look like they were struck with specially prepared dies or with polished planchets. What do you know cladking?

 

Hoot

[cladking]

Many of the SMS coins were struck on polished planchets.

 

Was it many or all of the SMS coins? These remain a bit enigmatic to me. Also, many of the business strikes, particularly the Jefferson nickels, from 65-67 look like they were struck with specially prepared dies or with polished planchets. What do you know cladking?

 

Hoot

 

Unfortunately I don't know too much of anything about these, it's merely observation. The mint apparently experimented quite a bit with these. No doubt they were looking for something that was easy to make and would satisfy collectors. I don't think the planchets for the bulk of these were truly polished though they may have been a little cleaner than most. I believe the reason the coins look so good is due to much higher coining pressure and that the dies recieved most of the treatment that proof dies did. One of the experiments you'll see fairly often especially on the '65 and '66 quarters is a polished planchet struck by what looks like a polished circulation strike die. These coins are extremely unattractive and extremely shiny, and usually are virtually mark free. Some of the polished planchets were apparently inadvertantly used to strike the more typical SMS coins. These are sometimes mistaken for proofs but were struck only once in most cases.

 

I have seen business strikes from these years which appeared to be struck on polished planchets also. There are also business strikes which apparently were struck on normal planchets with SMS dies.

[Leothelion]

Here's a frosted 64-D.

 

Leo

[Leothelion]

Here's a 60x pic of a 40-D prooflike Jeff. Here we can see the flow lines in the letters but the fields show no flow lines. The mirrors are very deep for this coin.

 

Leo

[Leothelion]

This one shows horizontal flow lines on this 50-P PL Jeff.

 

Leo

[Leothelion]

And this 51-S PL shows vertical flow lines.

 

Leo

[DonHeath]

Just as an aside to a pretty interesting conversation, the SF mint burnishes proof planchets with steel pellets prior to striking to give them as smooth a surface as possible. The proof planchets do not however have a mirrored surface. The evidence of this is the occasional off-centered proof strike error coin. The planchet is bright, but not mirrored.