Depending on the manufacturer of the folder you may at times find coins with streaks on the reverse. This is made by the glue also. This process is made so the glue that holds the cardboard with the slots is layed out in streams. This acturally saves on the amount of glue used to make a folder. Sounds trivial but when multiplied by hundreds of thousands of such folders, the savings is substantial. And don't forget the spit on the coins when using those folders.