To my collection of unusual library postcards I have added an aluminum postcard that depicts the former Carnegie building of the Manitowoc (WI) Public Library. Manitowoc received a $25,000 Carnegie grant in 1902 and the new Carnegie building opened in 1904. It housed the public library until it was replaced in 1967, and unfortunately was razed after that. A brief history of the Manitowoc Public Library is located HERE. The postcard was mailed on Dec. 5, 1905 from Manitowoc to Sacramento, CA. In the first decade of the 20th century when postcards were in their heyday there were some pretty unusual postcards that made their way through the postal system. I've previously written about leather postcards and wooden postcards. There is an interesting aspect to this aluminum postcard. It doesn't have a stamp or a postmark cancellation. That is because when it was mailed it was enclosed in a clear outer envelope on which the stamp was placed and cancelled. There is a statement on the address side of the postcard which reads: "Not Mailable Except Under Cover". All of these unusual postcards were probably a huge headache for the mail clerks that had to deal with them.