Newbie Questions: Luster

Info - somehow I missed this last repsonse & querry when it was posted. But because of its importance I will try to answer it now.

From a purely technical perspective yes a mirror does have luster because of the metal coating on the back of the mirror. But it is not like the luster on a coin.

Yes a Proof coin has luster, any and all freshly struck coins, or properly preserved coins, have luster.

Yes the flow lines make it so it is not as flat as a mirror. But it is close due to the polishing that the planchets and the dies receive. That is why you can see a reflection on it. It is worth noting that we are talking about Brilliant Proofs here for not all Proof coins are as reflective as them.

But it is the clarity of that reflection that makes the coin differ from a mirror. The clarity on the coin is distorted by the flow lines of the metal. So the reflected image on the coin is not as clear as the image in a mirror.

Yes you can see cartwheeling on a Proof coin. Cartwheeling is the reflection and refraction of light. On a business strike the cartwheel of light that you see is a wide band. On a Brilliant Proof coin the cartwheel is still there, but it is a much narrower band. That is because the band of light is more focused on the Proof.

Dunno, I guess it depends on who is there and how much they know about luster.

Yes I mean refraction. With a coin, you are getting reflection and refraction at the microscopic level. The surface of a coin is not perfectly smooth, instead it is a series of ridges. I use this as an illustration to explain what those ridges look like - /\/\/\/\/\. And the sides of each of those angled lines is not smooth either. That's because those ridges are created by the metal flowing, so the sides of the ridges are rough, but rough at the molecular level. Each molecule of the metal is exposed, and they are not smooth. So the light that hits these ridges comes off at all sorts of angles. It hits not only the ridge, but also the sides and angles of the individual molecules. So the reflected light bounces around at even more angles, some of it hitting the opposite ridge and the molecules on that ridge as well before it eventually returns to your eye.

And - all metal in coins begins to tone at the very instant that it stops flowing. The flowing of the metal exposes new metal to the air for the first time. Light pierces that toning and is thus refracted when it is reflected back to the eye. And the more toning that a coin gets the more refraction there is. And most metals are semi-transparent at the molecular level as well. So some light is refracted by the metal itself.

This refraction, coupled with the reflection of the light from all of those angles is what presents the eye with the cartwheel you see. And the smoother the surfcae of that coin is the more that band of light is narrowed and focused. The rougher it is, the more that band of light is widened.

Now hopefully, all of this makes sense.