A Beginners Guide to Identifying Proof Like Coins: A new technique

As a novice collector, something that I and many others struggle with is identifying a PROOF LIKE (PL) coin. This simple system I developed is a good starting point for understanding the question "Does my coin have a chance at being PL". This does not answer "Is my coin PL". You can also use this technique with slabbed coins unlike the traditional 4" reflection test.

Just to reiterate by using my technique you can come to two conclusions:
1. My coin MAY BE PL.
2. My coin IS NOT PL.

That's it!


I call it the LUX REFLECTION TECHNIQUE. Because we will be focusing on light reflection not image reflection like the typical 4" and 8" standards... and Lux is Latin for light!

FYI: If you don't care about the science skip ahead to where this comes into play or the set up.


A Quick understanding of reflections

A little background on reflection and the simple explanation of how it words will help us in determining if a coin MAY be PL.
The second Law of reflection states: "The angle which the incident ray makes with the normal is equal to the angle which the reflected ray makes to the same normal." As seen below.
(wiki)
Simplified it states a ray of light that reflects off of a mirrored surface will reflect off at the same angle that it it originally struck the surface. This is useful information that most of us already understand even if you don't recognize it. For example, if you took a mirror and stood at a 45 degree angle from it you would see a 45 degree reflection of where the mirror is pointing to like looking around a corner or using a periscope. This will later be applied.

The second concept of importance is understanding Diffuse reflection vs. Specular reflection. Simply put diffuse reflection is when light hits a non mirror like surface and gives it light reflection and provides the images we see, such as the sun illuminating a grassy field so we can see it. Exactly why we can not see anything in a pitch black room, without objects diffusely reflecting light our eyes could not pick up their images. Specular reflection is what you see in mirrors. An exact replication of the light that shined on the surface is reflected back. Exactly like looking in a mirror.
By using the information we know about Specular and diffuse reflection we know that if a coin that is more mirror like will give a more specular reflection. And a coin that is less mirror like will give a less defined or diffuse reflection.


How collectors currently home test PL coins

The above concept is currently how many collectors determine whether their coin is PL or not, the current home test is to see if your coin reflects an image from 4" or 8" distances. But the problem with this test is how clear does a coin have to be in order for the image to be considered reflected (or specular). And if you attempt to reflect through a slab then the plastic enhances the reflection.

WHERE THIS TECHNIQUE COMES INTO PLAY

Rather than using the idea of image reflection, my technique takes into consideration LIGHT reflection (yes images are actually light reflections but for arguments sake lets keep reflected images and reflected light separate). The concept is a metal surface that is more mirror like will reflect light in a less diffuse pattern and a more specular pattern. In order to view how diffuse/specular a coins light reflection is we will now use the second law of reflection. By Shining a light at a coin and holding that coin at a 45 degree angle to that light source you can reflect the light source another 45 degrees downward so the image is exactly 90 degrees onto your table. This should create an exact image of where the coin reflects light vs where it does not. A perfectly reflective coin should have a specular reflection heavily from the fields but not at the devices giving off a mirror image of the fields with a shadowed area of the devices.

Secondly, the old technique is impossible to use when wanting to view reflections of images through slabs. But using my technique the reflection of light off the slab does not matter because the amount of light reflected is even on all surfaces therefore if the slab reflects the light making the fields appear more reflective it will also make the devices appear more reflective. This means the contrast between fields and devices is the same ratio regardless of whether there is slab or not. Essentially, you will see the same amount of definition of the devices whether the slab reflects or not.


The set up:

100 lumen LED flashlight (any bright light that isn't too diffuse)
A regular piece of computer paper

This example uses 3 coins:

1. A dipped mirror like ~63 1882 Morgan
2. A (near) 64 PL 1879 Morgan
3. A ~MS 61 1899 Morgan with heavy luster
(If I had a PL coin or DMPL coin this would be easier, I'm sorry I used what I had available)

How to position coin and light


Procedure:
1. Turn off lights
2. Turn on flashlight
3. Shine into coin while holding coin at 45 degrees to light source.
4. Analyze results

Dipped coin:



Near PL coin



Lustrous MS 61



RESULTS and INTERPENETRATION
1. The dipped coin shows a clear difference in the mirrored surfaces of the fields and the devices. A clear example of very reflective fields on both the obverse and reverse. This coin MAY be PL. (if not dipped)

2. The near PL coin shows slightly less reflection in the fields but a clear crisp line between fields and devices. However, comparing the reverse to the dipped reverse you can clearly see reflection is lost. This coin MAY have a PL obverse but not a Pl reverse.

3. The very lustrous 99 shows no definition. This coin IS NOT PL.


Example with a slabbed coin I thought should've been PL.



Previously I had no clue since I could not use the image reflection test with the coin in the slab. Now I can clearly see the obverse MAY be PL but the reverse IS NOT.



Thanks for reading, I hope you learned a bit and can use the Lux Reflection Technique is your collecting futures!




Sourced and Images from wikipedia
https://en.wikipedia.org/wiki/Reflection_(physics)#Reflection_of_light

 

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Actually, it's Latin.

 

Oops you're right. ill fix that ha

 

Any feedback? Did anyone find anything interesting or learn something? I was kind of hoping this would help even if it's something little.

 

Yes, this was very informative. The science of it made me think, sometimes that hurts but yeah... I’m gonna have to test this method out, thanks for your time preparing this post.

 

Thank you, I appreciate it a lot.

 

Great experiment! I'm going to try when I get home

 

I hadn't considered this, but it's a clever idea. Thanks for the post.

 

Would same method work for determining cameo on Franklins?

 

If you see an enormous difference between the shadow of the devices and the reflection of the field you might have a cameo. If you don't then it's got no chance.

 

Actually, if you have a some Franklins to test would you mind showing your findings? I'd like to see how others coins appear using this method.

 

I wonder if toning would change the refraction of light? I have an 83 Morgan, I might give it a try.

 

I just use my finger and slowly pull it away from the coin until it becomes fuzzy. If that distance is 2”, then it is PL. If it is 8” or more, it is DMPL.

It works for certified coins as well, but you have to hold the coin at an angle to determine which reflection is on the coin and on the slab.

 

The 1879 S I used has toning around the edges. You can actually see the color in the reflection. If its still not to thick it shouldnt affect the coin. I've used this with coins that are more heavily toned and clearly not PL and there is almost nothing reflected.

 

I address this in the middle area, the problem with this technique (which you've pointed out) is that the slab can get in the way and it can be difficult to know what is slab or coin. Secondly for beginners that dont own any PL or DMPL coins, or dont have prior experience its hard to know how sharp an image needs to be before it is not considered a reflection. I believe you're probably very well versed in identifying so that technique is best for you. I just use this as a easy way to understand if my coin even has a chance. Like my 80 S I though did and now I can see the reverse clearly is not.

 

I tested the repeatability of your experiment, and it went very well.

I repeated your test using:

1. 1994-P PF69 Proof Silver Eagle
2. 1986 PF69 Proof Silver Eagle
3. 1883 No Cents V Nickel that I posted a question about yesterday
4. 1881-S Morgan that I pulled from grandpa's Whitman that looks pretty proof-like to me. But I'm still learning.

See attached photos, in order as listed above. Thanks

 

PS as you noted the reflective surface must be a diffusive surface.

 

shinny vs not-shinny

 

@Mitchell Wright
Very cool to see the proofs. I think that gives you a good idea about the Morgan. I think it may be PL. So you know now it's at least got a shot.

@CoinCorgi essentially yes, just using the science behind two types of light reflection to our advantage. Specular instead of diffuse.

 

I definitely have a few I'd like to check. And some very definite non-cameos to test alongside. Cool idea I'll post pics later.