A case or sleeve to hold a kiseru is called a kiseru-zutsu or sometimes simply a tsutsu and are found in five principal styles.
Most popular was the muso-zutsu, an oval or tubular, telescoping style consisting of a thinner top piece and a thicker bottom piece. Visually when a muso-zutsu is closed one sees a top piece that is distinctly thinner then the bottom piece. The popularity of the muso-zutsu probably stems from the fact that it can easily and snuggly fit pipes of varied lengths.
The aikuchi-zutsu is similar to the muso-zutsu except the top piece is of two diameters, the upper portion of the top piece is the same diameter as the bottom piece while the lower portion of the top piece is thinner then the bottom piece. This allows the top piece of an aikuchi-zutsu to fit into the bottom piece like a muso-zutsu but visually when an aikuchi-zutsu is closed the top and bottom pieces appear to be of the same diameter. Unlike a muso-zutsu however, the aikuchi-zutsu can not adjust to differing pipe lengths. Pipes too small will rattle around and pipes too large will prevent the case from closing properly. In terms of numbers the aikuchi-zutsu appears to be one of the least popular case styles, but then again the average aikuchi-zutsu also appears to be of a distinctly higher quality then the average muso-zutsu. All of which suggests that the aikuchi-zutsu was a custom made case fitted to a specific kiseru and the most prestigious case style.
The otoshi-zutsu is the second most popular style, it is a single hollow piece case, open at the top. Like the muso-zutsu it can fit pipes of varying lengths but there is always a risk that the pipe will slip out of the case as it has no top cover. I suspect that the popularity of this style of case not withstanding this 'structural' defect, was because the style was well suited to stag antler which Japanese artisans were particularly adapt at carving. (I have seen cases that appear to be otoshi-zutsu but with a flat, hinged cover. Most likely these are writing brush cases and not kiseru-zutsu).
The wari-zutsu is a variant of the otoshi-zutsu, differing in that the top portion of either side of the case is slit so that the upper sides of the case will tend to clasp the pipe and prevent it from slipping out. Functionally, this style case is superior to the otoshi-zutsu but it was not a particularly popular style, perhaps because the slit side design was not well suited to stag antler.
The senryu-zutsu is a single piece, largely open body case. The pipe is held in place with a notch that locks in the bowl and a ring that holds the mouthpiece. While this type of case has some flexibility to hold different sized pipes, it is often far more delicate and prone to breakage then the other style cases. Fairly consistently this type of case is carved so it will hold a pipe, bowl down, on a flat surface, it follows that this type of case may have had some use simply as a pipe holder in the home, (if only because the typical kiseru carried outside the home was shorter then the typical pipe rests of a tobako-bon).
Most all pipe cases appear to be intended for a 7" - 8" rao-kiseru, and very rarely for a nobe-kiseru.
The substantial majority of pipe cases regardless of style were carved of wood or stag antler, some by leading netsuke carvers (netsuke-shi). Stag antler and to a lesser extent, bamboo were particularly suitable for pipe cases since what was usually a drawback of those materials, hollow interiors, became an attribute. Ivory, and most especially elephant ivory on the other hand although far easier to carve, was seldom used because the lengthwise case demands resulted in significant waste of an expensive material. Lacquer cases are often found in the muso and aikuchi styles, the most common sort being clear lacquered woven cane, bamboo or ganpi (tightly twisted lacquered paper) and referred to as nagato-zutsu. Non-woven lacquer cases of the highest quality and in most lacquer styles are also found and treasured. Cloth and leather cases in the otoshi style are frequently found. It is said by one authority that until the mid 19th century most pipe cases and tobacco carries were made of leather or cloth. While few have survived, sources also tell us that prior to the 19th century coated, durable paper cases and carries were also very common and sometimes quite expensive. Indeed use of paper pipe cases and tobacco carries may have been more prevalent in the 19th century then we now believe, it's simply that they have not survived.
A final note should be added concerning pipe cases, like kiseru, as weapons. While rarely found, ‘defensive’ heavy metal pipecases may sometimes be found, as may be what appear to be aikuchi-zutsu but in fact pull apart to reveal a dagger (note though that confusion in this regard is quite possible as the aikuchi-zutsu style itself was an emulation of the Japanese cased dagger), lastly there are also teppo-zutsu, which are not tsutsu at all but rather guns disguised as an otoshi-zutsu.
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