Today I’m thinking about the problem of hair and fur. It’s a challenge of both technique and scale; you need to figure out how to handle your materials to make them look the way you want, but you also need to start with optimal materials.
The photos show three effects that can be achieved with the same material and same basic technique. They all use my go-to @sulky 12wt cotton thread, applied one strand at a time, then picked and brushed to make it fluffy. The shorter you trim it, the easier it is to create fluff with just a nylon brush; the longer the strands, the more you have to manually separate each strand, one at a time, into separate plies that are thinner and less twisted and thus have a naturally fluffy look. The shortest trim (less than a quarter-inch) creates a close-cropped, woolly fluff, the middle-length trim (3/8 inch or so) creates a cottony, bad-hair-day sort of look, and the long length (here about an inch long) can look like long fur, hair or, surprisingly, feathers.
This effect works pretty well, but it’s laborious to apply if you need a LOT of long fur or hair. I haven’t yet found a brush that effectively separates the plies in long strands, so separating each one by hand is required. Easy if you have a dozen strands; kind of a pain if you have a hundred (think long-haired dog like a Collie). So this leads to a search for thinner threads—is there a thread that gives a fine enough effect without requiring separation of every strand?
The options for thinner thread include products in 30-, 40-, 50-, 80- and 100-weight sizes. I’ll be experimenting with these over time. I have thread in the 30, 40, and 50 options and they seem too thick and stiff on preliminary examination for this purpose. They’re stiff, smooth and still thicker than the plies in 12wt thread. I’ve ordered some 80 and 100 to test (DecoBob and InvisaFil from @wonderfil) and am hopeful that they may work well. They are also fine enough to be used as carry-along strands to give a multi-colored look that is important for some animals (think tortoiseshell cats).
More info and comparison photos to follow as I gather and test all these materials.