How can I reformat a USB I used by USB to add as iso file into it.

sudo dd bs=4m if=my.iso of=/dev/disk1


Now I want to get the USB back to normal. but the erase button in Disk Utility is disabled. How can I reformat this
The following page has a lot of explanation on it but I've provided the quick steps below. Side note, try verify and repair and fix permissions in the app first to see if that does it. 

Erase disk via terminal

Start in terminal with this command:
diskutil list

Next verify and repair the usb drive with this command putting the disk name I where it says {volume name} (no brackets):
diskutil verifyVolume /Volumes/{volume name} diskutil repairVolume /Volumes/{volume name}

If good so far, try erasing with this command, replacing disk identifier with the name from the list in the first step (eg disk2):
diskutil eraseDisk JHFS+ Test /dev/{disk identifier}