Lot 147 United States SC#1581/1625, 1734/1743, 1811/1820 1975-1981 Americana Issue, 47 VFNH Singles With Shade & Gum Varieties. 2017 Scott Cat. $31.85 USD, Click on Listing to See ALL Pictures

47 VFNH singles from the 1975-1981 Americana issue, showing shade varieties & gum variations, such as shiny dex & invisible dull DAVAC, and also a grossly misperfed 4c, showing the top part of the curved inscription at the bottom of the stamp.
2017 Scott Cat. for very fine mint NH is $31.85
Starting in 1964 to 1967 some selected US issues are tagged with zinc orthosilicate , or calcium silicate in the case of airmail stamps. Both taggants can only be seen with short-wave UV light, which is dangerous to the eyes if viewed directly. Zinc orthosilicate glows yellow green, while calcium silicate glows red orange. All issues from the 1967 National Grange issue onward are normally tagged, and untagged stamps are generally errors, with the exception of the 1968 Airlift issue, and a few others. Gum was generally a shiny dextrine gum until the 1980's when an invisible DAVAC style gum was used for certain printings of the 1954-68 Liberty Issue coils and some values of the Americana issue, as well as definitives from the 1980's and onward. Finally, all stamps to 1956 were printed using the wet method, but during the life of the Liberty issue, dry printing was introduced, and many values exist both wet and dry. Generally dry printings have much sharper and lighter printing, as well as stiffer and glossier paper.