1948-D 10C strange step-like parallel lines on reverse, any insight?

[ryanrich]

I found this strange mark on the back of a 1948-D 10C of origin unknown to me, a raised series of parallel lines running through the bottom of RI in AMERICA on the reverse. Does anyone have any insight as to what makes something like this? They almost look like steps, and look to be behind the letters on top. I thought it was just a scratch on the planchet before striking but they look like little raised lines so I'm unsure, any insight would be appreciated! Let me know if I can take a better/closer photograph of anything!

Happy New Year!

[occnumis2021]

generically i/we call them metal flow lines and is just from such high pressure causing outward "fissures?" in the dies which either minimally or drastically increase over the dies life.

look up capped bust halves and see pretty much the most extreme version of this. not as pronounced in modern coinage with better dies and processes but they can still get fairly strong and not always going parallel outwards.

[ryanrich]

Wow, that's amazing! I had no idea! Thank you occnumis for dropping some major coin knowledge to start the new year!