Sometimes it’s desirable to have a high gloss, built-up finish on a fly, the heads of Atlantic Salmon flies being the classic example of this. Once done with multiple layers of lacquer or head cement, it’s now more easily accomplished with a layer or two of UV cure resin which is then cured with UV light.
The heads of flies, streamers in particular, are most often where a high gloss finish is desired but it also can be used to enhance the look and durability of say, a wing case, as on this nymph. Additionally, built-up high gloss finishes can be used along with thread wraps to add structure, like on this Barr’s Meat Whistle.
Low viscosity, penetrating adhesives such as regular head cement are primarily used on the heads of dry and smaller flies in order to simply secure the final thread wraps without adding weight or bulk. The thread wraps behind a bead head also benefit significantly from a thin, penetrating finish like head cement or thin UV cure resin.