Jumbali here. I just recently found a 1991 dime that has a straight side to it. To me it look an error but I am no coin buff. Has anyone heard of an error 1991 dime?
If it's a real error there will be a weakness directly opposite the straight line. This is called the Blakesly effect and occors because of the way the planchets are prepared. The flat discs are cut out of a sheet of metal and have to be squeezed between rollers to make the metal thicker where the rim will be and reduce the diameter for coining. This process is called "upsetting". If a planchet is defective when it goes through upsetting then there won't be any pressure on the wheels when it goes through and the metal won't pile up directly opposite the missing piece of the coin. This will result in weakness in this area. If this isn't present the coin is alterred.
