See below for details
This 12¢ value was printed by two printers:
The National Bank Note Company (1870-72)
The Continental Bank Note Company (1873-78)
Identifying which stamp belongs to which printer is a little challenging, but can be done. Here is a step by step guide
Detail shown below
The grill seen on the reverse of some stamps
If your stamp has the a grill on the reverse you have quickly identified the stamp. It is the first printing of this stamp from the National Bank Note company and is #140
There are two types of grills, the H grill and the I grill, the I grill being far less common, and as a result has a higher value.
If your stamp has a grill the button below to be taken to your stamp.
If your stamp has no grill on the reverse continue reading.