Question regarding luster and proof coins...

dan1ecu

Hi, Everybody -

Can anyone tell me if it's proper to speak of a deeply mirrored proof coin as having luster?

It seems to me that luster is often a determining factor in assigning a grade to a business strike coin. For instance, the difference between an MS66 and an MS67 could be that the MS67 has better luster. Are deeply mirrored proof coins evaluated in a similar way? If it's not "luster," per se, then what are some of the main factors that distinguish higher end proof coins? What is usually the difference between a PR66 and a PR67?

Thanks,

Dan

ziggy29

A proof coin can have some luster, but that's usually not its defining characteristic nor is it usually the most desirable. Generally we don't speak about luster in proof coins.

Luster is essentially light reflecting off of the flow lines in the metal of the coin; since the flow lines tend to radiate outward from the center, it results in the "cartwheel" effect. Because of the way proofs are minted, they don't usually cartwheel like business strike coins.

Instead of luster, for proofs we usually look at the reflectivity of the surface (how much is it mirror-like) and the contrast between the fields and the devices (are the devices frosted, i.e. cameo?) -- in addition to some of the same things you can look at for MS coins (hairlining, marks, blemishes, spots, et cetera). If a proof coin exhibits some luster, it probably doesn't have the strongly desirable deep mirror surfaces that usually characterize proofs coins (with matte proofs being an exception).

CarlWohlforth

Good reply Ziggy! Some dealers will say a proof coin is very lustrous but I think they mean reflective and don't really know what luster is technically. There are some proofs that have a bit of luster but they are the exception to the rule.

I think the perfection of the fields has a lot to do with the difference between a PR 67 and PR 68. While both will have almost no hairlines or imperfections the fields really have to be deeply reflective to get the higher grade.

mgoodm3

Old proofs often have some luster. The less deep the mirrors are the more luster there is. Should have very little luster on a cameo proof and almost none on a DCAM.

dan1ecu

I appreciate the replies, guys!

Dan

Shamika

<< <i>Luster is essentially light reflecting off of the flow lines in the metal of the coin; >>



Now this is interesting. I've always associated "luster" as basicly any kind of light that reflects off of the coins surface.

Thus a business strike has either "proof like" luster, "satiny" luster, or "frosty" luster (or is just plain dull thus having no luster).

Am I incorrect?

CarlWohlforth

Mint State business strikes can be proof like or lustrous. Morgan dollars are known for their cartwheel luster. The cartwheel effect is the "bow tie" of light that rotates around the coin as you tilt it under a light. Deep Mirror Proof Like Morgans don't have that effect. The fields are reflective and you can read printed text that is reflected in the fields. These DMPL coins do not have luster in the technical sense.

The PCGS grading guide says that proof coins can have luster due to die polishing. They mention there is a noticeable cartwheel effect on them. They catagorize all surface conditions as some kind of luster they even describe the lack of luster as "flat luster". To me they are overusing the term. I guess I just make a distinction between the huge cartwheels of some MS Morgans and the almost non-existant cartwheels seen on "watery" proofs.

JadeRareCoin

I made this post in a similar thread a couple of days ago:


Luster can be defined as the light reflected off of radial flowlines eminating from the center of a coin. The flowlines are the bi-product of excessive force/speed needed to strike a coin. The magnitude/intensity of the flowlines will depend on many factors, including but not limited to: size of the planchet, metallic properties, planchet preparation, force of the strike, speed of the strike, etc.

Some very well struck coins do NOT have luster (flowlines). For example, consider a modern proof coin that has mirrored fields. Why mirrored fields? 1) because of the specially prepared planchet and, 2) because of the much slower speed of the press, despite the obviously higher striking pressure.

You commented that "flowlines in the dies are the cause of luster", but it is not the dies that are flowlined, but rather the individual coins once struck. Remember that the working dies were hardened after preparation, and therefore would not likely pickup flowlines from multiple strikes. Flowlining (aka luster) on coins will and does vary from coin-to-coin. Have you ever seen 2 identical date Walking Liberty Halves sitting next to each other, both grading about the same, but one has much heavier luster? Assuming that neither coin has been cleaned, and both are truly mint state, we conclude that the more lustrous coin was struck with more pressure and/or at a greater press speed.

The 1857 half cent that you mentioned is just one of many coins that are known to not possess much luster. In the case of the 1857 half cent, I would guess that they were struck at a slower speed, hence the less obvious flowlining. Also you must remember that the mint only used one set of dies for the 1857 (C-1) to strike both proofs and business strikes. After striking the proofs, did the mint change the press set-up, or just continue striking business strikes on normal planchets? My guess is that the Mint just continued striking 1857 business strikes after the 200 or so proofs that were struck. I mean, why waste the time to change the press set-up? Just throw in the normal planchets for business strikes and start minting. That's why it can be very difficult to distinguish between an 1857 proof and a business strike.

The lesson here is that a coin lacking luster does not necessarily mean that it is of a lesser grade. The trick to determining the appropriate mint state grade on an uncirculated coin is in trying to establish how close the coin is to its original condition when struck. On 1857 half cents, grade on the strike and the originality of the surfaces.

Shamika

I stand corrected!