Hair Stacking and Other Applicable Stuff
All hairs have "scales" on the outer surface of their shafts. These scales are so unique from one animal to another that the Federal Bureau of Investigation (among other organizations) uses them for scientific identification of animal species that have relationship to an investigation.
As each hair shaft grows out of its hair follicle, these plate-like structures are laid down on the outer cortex of the shaft in particular patterns. I recommend that you add to your library Fly Tying Methods by Darrel Martin (ISBN 0-941130-40-1.) Among the wonders found in this book are microphotographs of a variety of tying materials that aid greatly in understanding why they do what they do. Note pages 75 and 76 where the scales on beaver and whitetail deer are shown. The difference between the two animal's scales is impressive. Beaver hair has somewhat random plates wrapped about the shaft. Deer hair scales look like fish scales, and lay on the hair from root end to tip essentially as a fish's scales lay on it from head to tail. (Note the illustration.) Why are they there? It is thought that perhaps the scales help to protect the skin from foreign matter. Since scales bevel away from the hair shaft in a direction toward the tip, this arrangement would hinder dirt from working down toward the skin. For dirt that did manage to get down to the skin, the scales would help to migrate it toward the hair tips and off of the animal.
To prove to yourself that scales are present, hold a single, clean Mule Deer hair between the thumb and index fingers of both hands. Under equal pressure, but not sufficient to break the hair, slide your fingers holding the hair away from one another. You will note that the hair remains with the fingers holding the root end. When demonstrating this many fly tiers have suggested it occurred because of the "hair taper" or "hair hardness near the tip." They are then instructed to trim off the hair tip past any visible taper and repeat the process. They discover that the hair still comes free in the direction of the now trimmed tip, not the root end. This graphically demonstrates the presence and direction of the scales. Here is another experiment that allows you to listen to the scales! Hold another clean Mule Deer hair firmly by the tip adjacent your ear. Slide thumb and index fingers of the free hand fairly gently over the hair of the scales toward the root end of the hair, "going against the grain." You will be able to hear the squeak of the scales as your fingers catch against them. If your reverse the hair end for end and repeat the process, there will be silence as your fingers slide over the scales in a direction of no resistance.
Scanning electron micrograph of a hair showing the scales. The tip of the hair is upwards in the picture.
If the point of this article is to discuss stacking hair, why waste time discussing scales? Scales have interplay in various aspects of fly tying. For example the reason that natural fur felts is a combination of three factors:
Realizing that this is an article about hair stacking, not dubbing the question is still remains: why waste time discussing scales? (I just couldn't resist throwing the dubbing stuff in!) Scales on hair provide numerous disadvantages and few advantages for the fly tier. More will be discussed with specific materials, but one item is appropriate to mention here. A reason, but not necessarily "the" reason, that some hair, even after cleaning, is difficult to stack (i.e., bucktail, calf) is because the existence and direction of scales on the hair is not taken into account. The resistance of individual hair's scales against adjacent hairs slows the stacking process. To verify this take a clump of clean bucktail and attempt to stack it. After 2 or 3 taps with the stacker observe your results. The hair will be moderately stacked, but likely not terribly even. Now take that same bunch of hair and invert the direction it is to be placed in the stacker. If you choose mess the bunch up a bit so that the root ends are definitely misaligned and then restack. After 2 or 3 taps take a look. The root ends will be just as even as they were when you first trimmed them from the hide. Why did the hairs slide easily against themselves in the direction of the root ends but not as easily in the direction of the tips? A major contributor is scales.
- structure of the fibers (ribbon-like and soft versus round and ridged)
- denier (weight for a given length) or simply put, hair diameter