This is from the quarterly fly fishing magazine by Scientific Anglers, Fly Fishing Quarterly August of 1991.
Finding The Answers: Positive, Neutral, and Negative Tying Materials by Gary LaFontaine
Security is getting so tight at airports that fly tyers as a group are coming under suspicion. How else can you explain the problems I had with the pedestal of my Regal vise?
A Security guard at the metal detector pawed through my fly-tying bag until she found the pedestal. “I can’t let you through with this,” she said, waving it triumphantly, “It could be used as a blunt instrument.”
I could see her point, immediately picturing myself grabbing the pedestal, rushing the cockpit, and screaming at the pilot, “Take this plane to New Zealand, to the South Island, where the trout are rising, or I’ll whip finish you!”.
Finally, with the help of a supervisor, both I and my fly-tying equipment were on the way to Reno, Nevada, arriving in time for a demonstration at the Reno Fly Shop.
Several people at the demonstration asked me to discuss the question of why some materials are special—or especially desirable. How do they add to the effectiveness of a fly?
The answer hinges on the observation that any material, over and above the color and shape it lends to a fly, has a negative, neutral, or positive influence upon success.
How can a material have a negative influence? The worst material in our underwater observation of flies was latex. A trout, feeding opportunistically, would take almost any drifting nymph that “hit him in the the mouth.” The only strong exception to this was a fly tied mainly of latex. The latex was a negative influence because somehow it made a fly look (to a trout) more like an inanimate object than a living entity. Most materials are neutral. They add color and shape to a pattern, but there’s no magic to them. Many dubbing mixtures, natural and synthetic, are drab enough to qualify as neutral. Some feathers, flosses, quills, and hairs define a fly but do not elevate it. Neutral materials lack the major qualities that somehow shout “life” to a trout, but they don’t look so unnatural that they deter a feeding fish.
Positive materials do possess those intrinsic lifelike qualities. Our underwater observation has pinpointed some of these special physical properties. Three major aspects are translucence, high reflectance, and water-repellence (the later strictly for dry flies).
Consider translucence. What our divers, and also apparently the trout, see in polyurethane packing foam is how it diffuses light and creates a soft aura. This perfectly mimics the fiery translucence of insects as divers as mayflies and ants.
Or consider reflectance. Nothing matches the ability of Antron and Cresland yarns, otherwise known as Sparkle Yarns, to reflect light. That brightness acts as a beacon to attract trout; it also matches the air bubbles that surround various insects in or under the surface.
Or consider water repellence. The hot item in fly tying this year is Cul de Canard, or Duck’s Rump feather. The natural oil on these feathers repels water so effectively that flies tied with them not only float extremely well but also gather a coating of natural air bubbles.
Bear in mind that a negative material may look natural and lifelike to you—latex being case in point—but to a trout it may look as lifeless and unappetizing as a twig. Thus occasional mistakes may be inevitable in experiments with new materials, but can be discovered (and thereafter discarded) after careful observation or, at least, trial and error.
Also bear in mind that, oddly enough, the really great flies are not made entirely of positive materials. The most consistent patterns are a blend of positive and neutral features. Maybe an imitation with all positive aspects ultimately fails because it’s too spectacular!
An imitation needs those mundane neutral parts to convince trout that the fly is really food.