Toning on a Faustina I silver denarius (RIC 360)

[Steven H]

I have a very general question about the toning on a Faustina I/Ceres silver denarius (RIC 360). I am as new as it gets with ancient coins, so forgive me if this is a question that sounds overly-uneducated.

Is it common to see both blue and gold toning together on a silver denarius, or is it something to be concerned about? I know toning is natural, and this toning is very subtle, but I just wondered if both colors (blue and gold) are commonly found on the same coin. Here is a picture of the coin in question:

[shanxi]

This effect is completely normal and quite popular.

The usual explanation is a "thin layer effect" similar to the colors of a thin gasoline layer on water.

In your case the colors are the result of a thin layer of oxidized silver. Thin means  below 200nm, in the range below the wavelengths of visible light.

When the layer becomes thicker the effect could disappear.


Something similar you can see here (especially Fig.3):

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-22-25-31545&id=306286

As you can see, blue is about 140nm, gold around 90nm


Or wikipedia:

https://en.wikipedia.org/wiki/Thin-film_interference

Here the steel example (last image) is interesting because it is similar to the coins.

[Steven H]

Thank you, shanxi - that makes sense to me.

[Robert_Brenchley]

As Shanxi says, it's just a light effect in a thin film of oxide. I've had similar effects appear on overcleaned silver, which continued to tone, and eventually turned black.

[Jay GT4]

Also  known as rainbow toning.

[stevex6]

I agree that it's probably from some sort of cleaning process ... however, there is also a chance that these are merely natural oxidation colours of the copper within the AR mix (for example, Bornite has a blue hue)

Yah, it's late and I've had a couple of vino, so my theories occasionally drip outside of the box

Cheers, fellas

Oh, and that's a gorgeous coin by the way (love the flow-lines)

 

[Diederik]

Very nice toning!

Frans

[arash p]

The coins is most likely genuine There is visible flow lines that indicate it was struck.