Non-toned legend shadow

[Nick]

Whilst browsing the Goldberg Coins website, I saw a stunning 1852 Gothic florin that reminded me of a question that I have wanted to ask for some time.

What causes the lack of toning around the top of the letters of the legend that almost appears as if it were an inverse shadow? I've seen many examples ahowing this effect, but can't think what the cause might be.

[davidrj]

Whilst browsing the Goldberg Coins website, I saw a stunning 1852 Gothic florin that reminded me of a question that I have wanted to ask for some time.

What causes the lack of toning around the top of the letters of the legend that almost appears as if it were an inverse shadow? I've seen many examples ahowing this effect, but can't think what the cause might be.

Interesting question!

Possibly an/oily greasy deposit laid down on the coin when new, subsequent wiping deposit off could leave residue between the legend and the rim but allow the rest of the surface to oxidise. Many years later a collector gives it a good wash in soap and water

Then again this could be total bullsh*t!

Weird things happen to coins, I have this penny where part of the legend has become incuse.

raised areas of a coin must suffer different pressures during the minting process than the field does, so I suspect there will be variations in the crystal size of the coin's alloy - under the right circumstances, such as long immersion in water, this could subtley alter the rate of chemical reactions.

Any metallurgists lurking?

David

Edited August 14, 2011 by davidrj

[£400 for a Penny ?]

I would think it is something to do with the stress the metal is put under during the strike, rather than any chemical activity myself.

[davidrj]

I would think it is something to do with the stress the metal is put under during the strike, rather than any chemical activity myself.

Both toning and corrosion are chemical reactions, but stress and crystal size will affect reactivity

see Stress Corrosion

"Stress corrosion cracking (SCC) is the unexpected sudden failure of normally ductile metals subjected to a tensile stress in a corrosive environment, especially at elevated temperature in the case of metals. SCC is highly chemically specific in that certain alloys are likely to undergo SCC only when exposed to a small number of chemical environments. The chemical environment that causes SCC for a given alloy is often one which is only mildly corrosive to the metal otherwise. Hence, metal parts with severe SCC can appear bright and shiny, while being filled with microscopic cracks."

David

Edited August 14, 2011 by davidrj