Today we have a couple of samples of First Day of Issue stamps and envelopes. The first one is from 1940, the 50th anniversary of Idaho statehood. The stamp depicts Idaho’s statehouse.
The second, from 50 years later, celebrates the state’s Centennial. Idaho’s state bird, the Mountain Bluebird is featured on the stamp.
This Bluebird cover was made unique by Mark D. Grabowski, an artist who specialized in painting little scenes on First Day of Issue envelopes. FYI, his envelopes sell for anywhere from $15 to $150 today, depending on rarity. I’m not sure what they sold for at the time of their creation.
According to our brainy friends at Wikipedia, “A first day of issue cover or first day cover (FDC) is a postage stamp on a cover, postal card or stamped envelope franked on the first day the issue is authorized for use within the country or territory of the stamp-issuing authority. Sometimes the issue is made from a temporary or permanent foreign or overseas office. Covers that are postmarked at sea or their next port of call will carry a Paquebot postmark. There will usually be a first day of issue postmark, frequently a pictorial cancellation, indicating the city and date where the item was first issued, and "first day of issue" is often used to refer to this postmark. Depending on the policy of the nation issuing the stamp, official first day postmarks may sometimes be applied to covers weeks or months after the date indicated.
Postal authorities may hold a first day ceremony to generate publicity for the new issue, with postal officials revealing the stamp, and with connected persons in attendance, such as descendants of the person being honored by the stamp. The ceremony may also be held in a location that has a special connection with the stamp's subject, such as the birthplace of a social movement, or at a stamp show.”