Coin Cracks

[James Cameron]

I notice in alot of silver coins. Cracs in the patina. Sometimes they look like wedges, somtimes like large cracks in dryed mud. They dont appear to be from impacts.
What is the cause of cracks like this on silver coins?
I have attached some pics of coins i picked up with examples of these markings. :)

[Kramer]

Well...what causes cracks in silver in regular I can answer on that, cause I am a goldsmith.

The material it self seems to be cracking up, why? Its very simple, while forging the coin or any piece of silver, it has been to cold during the developement, and cracks up.

The cracks can get larger during aging, and while using the material, in this case the coin itself. There could be some tensions in the material. Cause its not pure silver, the copper also causes tensions togheter with silver and zink.

Its like if you hammer a pice of metal without heating it up, it will crack sooner or later, you push the material to its limits, until it cant hold togheter.