Old coin which fluoresces under short wave UV.

[sjastro]

I took images of a 1947 Australian Florin coin under fluorescent, short wave and long wave UV lighting.
What I find puzzling is why the coin should fluoresce in the first place.

The coin has a composition of 50% silver, 40% copper, 5% nickel, 5% zinc.
The coin probably has a tarnish but why this should fluoresce at 254 nm is a mystery to me.
The blue specks in the 365 nm image are due to microfiber contamination.
Any suggestions to what is going on?
No other coins I have imaged exhibit fluorescence.

 

[Tinker Grey]

I have no idea, but I look forward to hearing from someone who does. Cool photos!

 

[Lost4words]

Its probably the copper and age of the coin.

 

[Occams Barber]

Looking at the photo the fluorescence is on the low points of the coin's surface. It appears to have 'rubbed off' the raised areas of the text and head image.

This suggests that:
1. the fluorescence is not integral to the original casting, i.e. it's not in the metal of the coin
2.the fluorescence is some sort of coating presumably added after casting
or
3. the surface metal of the coin has been directly affected by something causing the fluorescence. Perhaps immersion in a chemical or exposure to mildly radioactive material causing a change in the surface metal of the coin resulting in fluorescence.

Since the coin has been in circulation for a long time and still retains fluorescence in the lower surface areas I lean towards 3.

OB

 

[SelfSim]

Bioflourescence from trace organics .. maybe oil from fingerprints?

From Sherloc description:

For Spectroscopy, it utilizes a NeCu laser to generate UV photons (248.6 nm) which can generate characteristic Raman and fluorescence photons from a scientifically interesting sample.

 

[essentialsaltes]

Aha! After considering and discarding several ideas. I googled my way to...

Apparently coins are sometimes fluorescently tagged to follow them through vending machines or the like.

Fluorescent Invisible Coin Lacquer 1 oz

 

[Occams Barber]

Aha! After considering and discarding several ideas. I googled my way to...

Apparently coins are sometimes fluorescently tagged to follow them through vending machines or the like.

Fluorescent Invisible Coin Lacquer 1 oz

A brilliant piece of sleuthing old chap.

OB

 

[Questioning Brother]

It could also be some kind of hydrocarbon residue. Hydrocarbons fluoresce under UV light

 

[SelfSim]

Aha! After considering and discarding several ideas. I googled my way to...

Apparently coins are sometimes fluorescently tagged to follow them through vending machines or the like.

Fluorescent Invisible Coin Lacquer 1 oz

Chemical composition is here in the product spec sheet.
(Looks rather nasty actually).

 

[Halbhh]

I took images of a 1947 Australian Florin coin under fluorescent, short wave and long wave UV lighting.
What I find puzzling is why the coin should fluoresce in the first place.

The coin has a composition of 50% silver, 40% copper, 5% nickel, 5% zinc.
The coin probably has a tarnish but why this should fluoresce at 254 nm is a mystery to me.
The blue specks in the 365 nm image are due to microfiber contamination.
Any suggestions to what is going on?
No other coins I have imaged exhibit fluorescence.

As a couple have pointed out, organics or hydrocarbon. So, it could be just rubbed on coating of organic stuff maybe. (not an area I know much, but I know we've used once a blacklight to find dog pee on carpet in our house)

 

[SelfSim]

Looks like its prime constituent organic chemicals are readily bio-degradable in water or soil.

One might wonder why the flourescence/organic residuals still remain after such a long time, given the age of the coin(?)

 

[sjastro]

Thanks for the responses much appreciated.

The problem I have with organic coatings it should also be fluorescent at 365 nm longwave.
Even @essentialsaltes "Acme" coin lacquer specifies this.

It fluoresces a brilliant green when exposed to either longwave (UV) or shortwave (UV) radiation.

 

[SelfSim]

Thanks for the responses much appreciated.

The problem I have with organic coatings it should also be fluorescent at 365 nm longwave.
Even @essentialsaltes "Acme" coin lacquer specifies this.

Interesting.
The spec sheet for their own detection UV lamp (which is sold with the coating) is here. It says:

SIRCHIE shortwave UV lamps utilize low-pressure mercury lamps, which emit radiation in the UV-C (254nm) spectrum.

But then, on the product page, it says:

• Peak Wavelength: 365nm

• Bulb: Longwave UV-A black light type (F4T5), 4-watt

 

[Occams Barber]

One might wonder why the flourescence/organic residuals still remain after such a long time, given the age of the coin(?)

While the coin is old, the coating may be fairly recent.

OB

 

[SelfSim]

While the coin is old, the coating may be fairly recent.

Yes .. but 'why?', I ask .. why might it be so?
Its a mystery!

 

[essentialsaltes]

I agree with OB's analysis in post #4.

It doesn't look very dirty or tarnished or patinated, so I have to think it's a 'coating' rather than an actual chemical transformation of the coin metal. But what coating? If it was oil from grubby hands, all coins would look like that.

So maybe some rare soil from a mining site or something. Or some form of that commercial coating, maybe a mixture they don't sell anymore that's even more dangerous!

 

[Occams Barber]

Yes .. but 'why?', I ask .. why might it be so?
Its a mystery!

You're obviously related to the late, great Julius Sumner Miller.

Why is it so!!!!!!!!!!!!!!

OB

 

[SelfSim]

You're obviously related to the late, great Julius Sumner Miller.


View attachment 294165
Why is it so!!!!!!!!!!!!!!

OB

An absolute legend!! (Responsible for many choices I took in life).

 

[Bungle_Bear]

An Australian coin with a mysterious glow?

 

[sjastro]

I took a microscopic image of the coin under fluorescent light in the region of the top edge of King George VI's head corresponding to the blue/green boundary in the shortwave UV image.

The darker region corresponds to the green in the shortwave UV image.

A cropped close up view of the centre of the image in the boundary region reveals the following.

It doesn't look like a lacquer to me.
I would have expected the darker region corresponding to the lacquer to have a smoother glossier appearance.
Instead it looks to have a more crystalline appearance, or maybe I'm exhibiting a form of confirmation bias.