I am inspecting my collection and would like to share a few very useful links-articles. Please kindly share your knowledge too. Thank you.
Super informative and useful Identification Guide for Two Cent United States Postage Stamps http://dubinweb.com/USpostagestamps/twocents.html
WASHINGTON/FRANKLIN STAMPS OF 1908-1922http://www.jamesdire.net/W-F.html
"The "Washington/Franklin" series of United States postage stamps of 1908-1922, also known as the "Third Bureau Issues", are perhaps the most difficult US stamps to identify. In addition to new techniques for printing (i.e. rotary press, offset) and ways of offering stamps to the public (coil stamps) a new watermark (single-line USPS) was used for the first time. Additionally, an odd type of paper, known as "bluish" paper, was used for a brief period in 1909.
There are four major elements that need to be understood to conclusively identify Washington Franklin stamps:
Design: Five designs—A138, A139, A140, A148 & A149. See Section 1 below.
Perforations: Imperforate, perforated, and both horizontally and vertically perforated coil stamps. See Section 2 below.
Watermarks: Single line, double line, or unwatermarked. See Section 3 below.
Press Type: Flat plate, rotary or offset. See Section 4 below.
There are four minor elements that also need to be understood:
Paper: Two varieties—wood pulp and "bluish" paper. See Section 5 below.
"2 CENTS 2" Types: Nine types—I, Ia, II, III, IV, V, Va, VI and VII. See Section 6 below.
"3 CENTS 3" Types: Four types—I, II, III and IV. See Section 7 below.
Design Size: 19½ to 20mm X 22mm—only important in identifying two rotary press stamps, Scott 545 & 546. READ MORE
Washington/Franklins were printed on paper that was marked with single line watermark (190), double line watermark (191), or unwatermarked.
Intaglio printing, also known as "recess printing", is done from a plate that has lines etched or carved into it. When ink is applied to the plate, it collects in these lines and grooves, then after the surface of the plate is wiped clean it is run through a press under pressure. The pressure forces the ink from the grooves in the plate onto the paper, which form tiny ridges that, when dry, can be felt with a fingernail drawn lightly across them. A flat plate press, as its name suggests, utilizes a flat printing plate that is run through a press, then re-inked, wiped, and run through the press again. A rotary press utilizes a printing plate that has been formed into a cylinder, which allows for faster feeding of the printing sheets through the press—the plate is inked, wiped and impressed into the paper in one continuous action. Because a rotary press plate has been rounded, the image will be somewhat distorted. For stamps this means that the design will be slightly higher or wider than it would have been on a flat plate press. Also, the difficulty inherent in inking and wiping a rotary press plate while it was in motion meant that early rotary press stamps usually show a considerable amount of "plate tone", a sheen of ink that would transfer from the incompletely cleaned plate onto the stamp. See illustration below.
Offset printing is a fast, reliable and efficient method for printing. It was first used for printing stamps during the World War I as a cost-cutting measure, however the stamps, which lacked the fine detail of intaglio printed stamps, were unpopular with the public, who considered them ugly and cheap-looking. The use of offset presses to print stamps was discontinued in 1919, although offset was later re-introduced for printing stamps with marked success.
The image of an offset-printed Washington stamp is coarser and less detailed than an intaglio (i.e., flat or rotary press) printed stamp. Also, the ink lies flat on the surface of an offset printed stamp, while intaglio printing leaves a fine ridge of ink on the paper. In addition, some of the colors in the offset Washingtons are sharp and even garish. See below for general characteristics of offset printed stamps.