Watermark Check : You will need to check the watermark on this stamp. Since these stamps were printed by the flat plate method, there is no need to check printing method unless the stamp is suspect. These 3¢ perf 12 stamps are all type I.
|12||double-line (blue paper)||359|
The blue paper, Number 359, is actually a dull grayish paper. The stamp must be double-line watermarked. Fortunately, double-line watermarks are hard to miss, if you don't see one the stamp is suspect. If you think your stamp is the blue paper variety, you should have it certified. Even faulty, poorly centered examples of this stamp command a premium far in excess of the certification fee.