Does sunlight have any affect on coins?

BowTieCoins

Thanks,
Katrina

GTOster

Sit them in a window sill and watch them turn Colors
I have a morgan 1921 sitting there for about 9 months now it is turning very nice
I would take a pic but I want to leave it for a Year
The colors are a honey gold to a light Purple
Way Cool
Paul

kieferscoins

I know it sure can affect slabs, turning them a yellow color and fading the label big time.

Cameron Kiefer

relayer

Yes

Conder101

I don't really know. I'm not aware of any good research that has been conducted to find out. The bit about putting a coin on the windowsill and watching it change color is true, but might it have turned on the sill even if the sunlight was not shining on it? And what would the mechanism be for the light causing the toning? A coin with strong sunlight shining on it would be warmer. Is it the light causing the toning or the increased temperature that allows chemical reactions to proceed faster? Bright light shining on metal can knock electrons from the surface of the metal. Could this change the chemical reactivity of the coin? Is sunlight bright enough to knock the electrons off the surface? Is the sunlight causing other surrounding materials to decompose or outgas and those things cause the toning?

BAJJERFAN

The sunlight [which BTW contains all of the possible wavelengths of light] will probably make the contaminants in the air a bit more reactive and would be expected to accelerate any toning which might occur. Sunlight on a coin in an evacuated glass chamber would be expected to have no effect.

Shamika

<< <i>I know it sure can affect slabs, turning them a yellow color and fading the label big time. >>


This is due to UV degradation. If the plastic is incorporated with UV stabilizers, the yellowing will be delayed, but eventually the stabilizers are used up an the resin will yellow.




<< <i> Sit them in a window sill and watch them turn Colors >>


The color changes are due to heat (IR radiation) and off gasing of the paint/plastic and/or wood from which the window sill is made. Pollutants in the air (SO2) also contribute to a large extent.

Strickly speaking, sunlight shining on metal with nothing else in the environment (air, water, pollutants) will do nothing to change its color.

BowTieCoins

Thanks for your responses!

Katrina

airplanenut

I agree fully with what Shamika said... it's the heat, not the light.

jcping

Absolutely YES.

86elcaminoss

All silver coins get hot in direct sunlight

BryceM

Well, most coins don't really look all that nice in sunlight. Back before I knew better I tried to photograph some outside. They looked terrible.

Philosophically, it left me wondering if that's what they really look like. Certain people look better in dimly lit rooms than they do out in the open too.

Steven59

I was going to reply but I've learned to check on when the threads were first started - this is one of the older ones I've see as it's from 2004. Interesting topic but is it time to start a newer version?? When is old TOO old?

Paradisefound

This is an 18 yrs old thread 🤔 but I bet the sun still does the same thing on things 😬🤣 May makes coin sweat

P0CKETCHANGE

@Steven59 said:
I was going to reply but I've learned to check on when the threads were first started - this is one of the older ones I've see as it's from 2004. Interesting topic but is it time to start a newer version?? When is old TOO old?

Certainly it’s too old when the OP hasn’t logged into the forum in almost 16 years.

logger7

I've especially found that lightly cleaned coins or coins with hairlines are helped by putting them raw on a sunny windowsill. Two examples; an old holder PCGS $20 in MS63 that came back cleaned from NGC when cracked out. On the sunny windowsill and a couple months it was good enough to send in and it came back 64. Also had an 1899-s $10 in an NGC 63 holder over 20 years ago. In a place with indirect sun it looked to me that a light scratch toned over.

amwldcoin

I think one of the things not mentioned is the temperature changes the coin undergoes.

Onastone

@Steven59 said:
I was going to reply but I've learned to check on when the threads were first started - this is one of the older ones I've see as it's from 2004. Interesting topic but is it time to start a newer version?? When is old TOO old?

No wonder I didn't recognize any of the posters!! I thought that was odd.

@GTOster said:
Sit them in a window sill and watch them turn Colors
I have a morgan 1921 sitting there for about 9 months now

9 months and 18 years!!! How did this experiment turn out???

Paradisefound

First I thought I would have a Coin GF ….. Katrina? since @Kkathyl has not been active since early this year 🤔

@Onastone said:

@Steven59 said:
I was going to reply but I've learned to check on when the threads were first started - this is one of the older ones I've see as it's from 2004. Interesting topic but is it time to start a newer version?? When is old TOO old?

No wonder I didn't recognize any of the posters!! I thought that was odd.

@GTOster said:
Sit them in a window sill and watch them turn Colors
I have a morgan 1921 sitting there for about 9 months now

9 months and 18 years!!! How did this experiment turn out???

Onastone

@Paradisefound said:

@Kkathyl has not been active since early this year 🤔

Yeah, another missing member...I miss reading her posts.

Sapyx

Sunlight has an odd effect on silver. Many silver compounds are photoreactive - they turn dark on exposure to sunlight, or bright light generally, but particularly the blue to ultraviolet wavelengths. One of the main 20th century industrial uses of silver was in photography, as many photographic techniques exploited this tendency of silver compounds to turn dark; this is how black-and-white photographic negatives are made. Positive images are then produced by shining light through the negative onto a second piece of photographic film. The rise of digital cameras has almost eliminated this major source of consumption of silver in society. It's also why most silver chemicals come in amber-glass or opaque plastic jars when you order them.

The darkening is actually caused by molecules of the silver compound breaking down into nanoparticles of metallic silver. As such, it's not likely to be noticeable on a piece of solid metallic silver, like a coin, unless the layer of silver compounds is particularly thick.

This photochemical property of silver generally has little effect on coins, since most coins are exposed just in everyday use to enough light to turn whatever compounds might be sitting on them, black. And silver sulfide, the primary component of tarnish, is black to begin with. Theoretically, if you have a coin that's spent years in darkness or in dim/red light, in a strange environment (like perhaps a swimming pool chemical storage cupboard where the air is high in chlorine gas) and you suddenly brought such a coin out into bright sunlight , it might rapidly darken in colour. But as a general rule, casual exposure to sunlight for a few minutes isn't going to hurt a silver coin.

Storing a coin in sunlight for months or years can have a deleterious effect on a coin, but, as noted by the ancient ones above, this has more to do with the heat accelerating any possible chemical reactions, and/or the sunlight's effect on the surrounding environment (eg. causing outgassing of volatile chemicals from nearby wood or plastic).

Any budding coin scientists wanting to experiment, will need some controls: take your sunny location, and place down four identical-looking coins: a raw coin out in the open (no holder, album, etc), a coin in a 2x2, a coin in a Whitman or similar cardboard folder, and a coin in a slab. Come back in a few months, and see which coins have "turned", and which haven't. Hypothesis: the ones in the air-resistant containers (the 2x2 and the slab) will show little or no effect; the ones exposed to open air will have turned dark with tarnish.