Under Construction May 2011


Castor canadensis


Length: 50mm max (Mayer 1952), 65mm max (Tumlison 1983), 40-100 (Adorjan and Kolenosky 1969), 63mm max (Moore et al 1974), 40-55mm (ASM #1), 45-55mm (ASM #5)

Diameter Range: 190 microns max  (Mayer 1952), 189 microns (Moore et al 1974), 100-165 microns (ASM #1), 140 microns (ASM #5)

Medullary Index: about 0.33 (Mayer 1952) 0.35 (ASM #1) 0.41 (ASM #5)

Medulla:  Less than a third the diameter of the shaft (Mayer 1952). 35-40 microns in diameter (ASM #1) Medulla appears to be continuous with what Brown ( 1942) describes as a “froth” , which consists of “various sized bubbles” some of these bubbles are air filled and some are not. The medulla has the quality of many fine squiggly stacked lines (like an Egon Shiele drawing) with clusters of color ranging from brown to a light grey distributed throughout (ASM #1).  The cells of the medulla are easier to see in polarized light where they appear as “H” shapes and elongated “X” shapes with tiny bubbles in filling the voids. (ASM #1) Medulla rather skinny, and the edges are wavy and not smooth.  Closer to the tip the medulla might have gaps. (Teerink 1991). Can be hard to see individual cells, appears more like a light/dark mottled look.  Edges of medulla are squiggly and interrupted as it tapers out near the tip. (ASM #5) Medulla might be fragmental or absent right before the shield (Moore et al 1974)

Color: Unbanded. Has a reddish brown color distributed throughout the cortex with darker brown granules distributed throughout (ASM #1).

Scales: Torn paper-like or seismograph like scales with many points to each scale. The scales are very undulose overall. The scales do not change much throughout the length of the fiber, but do appear to be closer together towards the distal end of the hair (ASM #1).  Scales have very jagged irregular edges and deep valleys and are closely packed for the entire length of the shaft, but the edges do get smooth near the tip (Teerink 1991).


Length: 10-20mm (ASM #1) Sheared 10-15mm (ASM #2) 20-25mm (ASM #5)

Diameter Range: 10-12.5 microns (ASM #2) 10-17.5 microns (ASM # 3)

Medullary Index: 0.5 (ASM #2) 0.5 (ASM #3)

Medulla: Bead-like medulla. Medulla appears like stacks of “Q”s interlocked, giving an appearance of a medulla that is somewhere between the uniserial ladder and a string of beads. (ASM #1).  Cargille reference set sample (ASM #3) had combo of hairs with elongated dark bead-like medulla cells and no pigment visible, and slightly wider hairs that have streaky brown pigment and a sporadic, highly interrupted medulla.

Color: Some of the fibers have a reddish brown streaky quality distributed throughout the cortex

Scales: Some of the mounted fibers show flaring pointed scales, while others are not apparent-scale cast may be necessary (ASM #2).

Macro Qualities: 37-45” long (Forsyth 1999) 3-4 feet long including the tail (ADF&G 2008).  Prime when water is the coldest in early spring.  Best beaver fur is in the late spring?  In the winter, there are dark spots on the head and rump.  In the fall, they are dark on the back and have scanty guard hair.  Females have darker pelts? In sheared beavers the guard hair is plucked and shearing cuts off the kinky underfur tips that have a tendency to mat. Shearing also makes the fur look more like otter.  The base of the underhair fibers on the belly are silvery, and the shearing is sometimes done closer in this area to bring out the silvery shade. The belly of the beaver is always well-furred.   Good “serviceability” according to Bachrach (1953) The guard hairs seem to appear in clumps that are tight together where they emerge from the skin but splay out towards the tips.  The underfur is often a pale brown gray and has kinky curly brown tips.  (ASM #1) Guard hairs may have a short black tip and a long band of lustrous brown (Stains 1958).  Tip of hair from a beaver’s belly tapers gradually and evenly, while tip of a hair from a mink’s side mink tapers abruptly (Stains 1958).  Samet (1950) says that beaver was an early substitute for otter, with the underfur pulled out and only the guard hairs used.  This seemed odd, as the guard hairs might have seemed rather sparse?  He reports that ironing will straighten curly areas during processing.  Underfur is lighter than guard hairs.  Because the guard hairs are often plucked, beaver fur will mat with exposure to the rain.  Highest quality fur felt hats are made from beaver fur.  Lower quality are made from rabbit.

Cultures: For example: Yup’ik upriver hunters (p.245) Used as boot soles in tundra regions.  Beavers skins also used for headgear (p.258) from  Fienup-Riordan (2007) Yuungnaqpiallerput: The Way We Genuinely Live.  Masterworks of Yup’ik Science and Survival.  Anchorage Museum Association. 

Notes: ASM #1 is from the ASM education collection pelt ring, ASM #2 is another piece from the pelt ring, ASM #3 is from Cargille Reference Set F-5 commercial furs, ASM #4 is from an old slide in the ASM conservation lab, ASM #5 is from the Juneau-Douglas City Museum touchboard. Pelts often sheared for commercial use.  Bachrach (1953) says that the industry clips the tips of the underfur to prevent matting of those kinky tips. 

Troubleshooting:  Bear hair has scale margins much farther apart?  Medullary index in the rodents tends to be 0.6 to 0.9, and a narrower medulla might be a useful clue for the beaver and the raccoon, whose medulla is in the 0.3 to 0.4 range.  Beaver guard hair often has a golden yellow (almost glowing) appearance to the cortex, and the medulla may be interrupted.   Unfortunately, the guard hair is sometimes plucked or sheared from beaver fur when used on artifacts and garments.  Samet (1950) describes “mouton” as a beaver-processed sheepskin where shearling lab (fur after its first shearing) has certain qualities similar to beaver or fur seal.

Range: Mostly interior, Southeast panhandle, and Kenai peninsula (Forsyth 1999)  Most of the forested portions of the state.  Introduced in the Kodiak area in 1925. (ADF&G 2008)

Names: Order Rodentia (the rodents)  NOT the mountain beaver, who lives further south (Forsyth 1999)  French beaver is actually rabbit plucked and dyed to look like beaver (Samet 1950).  Velvety soft pile underfur such as comes from beaver is sometimes called “duvet” by the fur industry.

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