1944 Brass Threepence What Happened

[UPINSMOKE]

Picked this up the other day and would like to know what has happened to this. Not come across anything like this before. I am sure one of you will give me the answer. 

[mrbadexample]

Is it of a normal weight and thickness?

[UPINSMOKE]

7 minutes ago, mrbadexample said:

Is it of a normal weight and thickness?

It is thinner than a normal brass threepence and weighs 4.07 gms.

[Rob]

It is corroded by whatever method. Dissolving the surfaces in an acidic solution will retain the detail, but this becomes progressively thinner as the corrosion will dissolve the detail perpendicular to the surface at any point, i.e. from the side of lettering too, thus narrowing the character.

This has been discussed several times previously.

[Peckris]

Yes, it looks like a classic acid attack. Here's a 1929 shilling:

Acid corrosion typically makes the coin thinner, but the detail is kind of still there, though spidery in appearance - it doesn't show the normal wear patterns you'd expect through circulation. That shilling is as thin as a wafer.

[Rob]

It is because you will reduce the surfaces by a roughly equal amount. so if you remove say 0.25mm of metal from the surface, the diameter will reduce by 0.5mm, the thickness will reduce by a similar amount and the removal of 0.25mm from both bevelled sides to a character will result in a thin spidery character just as above. You also see the rim has thinned due to attack from three sides. Another thing I have seen on occasion is a 'moat' around detail which I have put down to metal flow causing stress cracks at the microscopic level allowing the ingress of reagent resulting in a greater amount of corrosion at these points.

Edited June 28, 2018 by Rob

[UPINSMOKE]

Thanks, guys for the explanation very interesting. I thought it was something to do with when it was struck, shows how much I know Back to school for me then.