Watermark Check You will need to check the watermark on this stamp. However, these stamps were printed by the flat plate method and there is no need to check printing method.
|double-line (blue paper)||364||(see below)|
|double-line (coil stamp)||356||can be manufactured by trimming the top and bottom perforations from either Number 338 or Number 381|
The 10¢ Washington coil stamp, Number 356, can be easily faked by trimming the top and bottom margins from the 10¢ sheet stamps, or simply the top or bottom margin if the sheet stamp has an existing straight-edge. The altered straight-edge stamps are particularly dangerous since they can approach the proper size for this coil stamp, that is 25.0mm or larger, measured top edge to bottom edge. This stamp is known as short as 24.2mm, but these shorter examples are rare. Any 10¢ Washington head coil stamp under 25mm tall should be examined carefully. The coil can also be manufactured by trimming the single-line watermarked stamp, but the lack of a double-line watermark would be a dead give-away to anyone willing to check.
The 10¢ coil is usually found with yellow or light yellow color. Dark yellow or orange yellow copies are unusual and therefore suspect.
Interestingly, guide-line pairs are a different matter. If the stamp has a genuine guideline it must be a genuine 356, since there is no imperforate stock from which this coil can be manufactured. A piece of thin foil pressed gently over the guideline will reveal if the guideline is genuine (see: printing methods).
We would highly recommend purchasing the 10¢ coil only with certification or from a reputable seller.