The most common material used for canteen covers, for BOTH Federal and Confederate was rough gray jean cloth or wool. This material would oxidize with time and develop into almost a "camel" color brown. Other types of tan, brown, or gray jean cloth were also used for covers. Importantly, federal canteens with sky blue covers and dark blue wool covers were rare. Unfortunately, there is a prevalence of dark blue or sky blue canteen covers in re-enacting today. Dark blue wool was very seldom used for canteen covers because it was fairly expensive and usually reserved for the making of frock coats and sack coats. Jean cloth was very inexpensive, yet durable, material - and therefore more practical for the construction of canteen covers.
Just prior to the War the Utica Steam Woolen Mill of Utica, NY produced canteen covers, the cloth was referred to simply as "canteen cloth". According to "those in the know" (and the article from which this information comes from; Company of Military Historians) canteen cloth (it's assumed) was just a cheap woolen or satinette material. It probably differed in color from bolt to bolt, lot to lot, but was generally light blue or gray.
It is thought that the sole purpose of the cloth material was to help keep the contents of the canteen cool (dunk the canteen and the cover absorbs the water, hence keeping the water inside the canteen cool...) So to use anything more than inexpensive cloth would have been a waste.
Obviously the massive build up of troop at the onset of the War meant supplies needed to follow suit, including covering materials for canteens.
One needs to remember that canteens were a utilitarian item, so we shouldn't apply any standard of uniformity to it. Even in 20th century warfare not everything was color matched... Check out the numerous shades of "khaki" and "olive drab" of World War II and that proves the point.
Anyway... canteens needed to be produced by the hundred of thousands if not millions, and they needed to be covered, so the government and those producing the canteens used basically any suitable material. Obviously cheap woolen and satinette was the obvious choice, however striped upholstery material was used, as well as worn out overcoats and other uniforms as well as blankets and so were the scraps from making uniforms from the cutting room floors of the depots, arsenals and manufacturers.
Most would agree that the use of sky blue and dark blue for canteen covers is over represented in reenacting today, however those materials were used. I guess the only real accurate way to determine historically the percentages of canteens that were covered in sky blue vs dark blue, vs gray or brown, one would have to jump in a time machine and go back for a look.
Incidentally, the article goes on to state (in a description of the corrugated "bulls-eye" canteen, which was of course manufactured in far less quantites than that of the Pattern 1858 "smoothside")... "...the typical Pattern 1862 canteen can be described as follows: corrugated with 5 or 6 rings, a cord tie for the stopper,a one or one and one-half inch web strap and a cover of almost any color, but predominantly sly blue or gray."
For more information read
"The Civil War Issue Canteens: Patterns of 1858 and 1862, by Earl J. Coates in the Fall 1995 issue of Military Collector and Historian, Journal of The Company of Military Historians. Vol. XLVII, No 3.
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