While I was getting this cutie ready for eBay, it occured to me I could snap some pictures and give a demonstration of my current method for hairing a mask. (This mask is available at auction on eBay until March 15, cheap because it's a materials test and too heavy to wear.)
So essentially I divide areas to hair into three parts: the back of the mask, where I can use the wefted hair; an area roughly 2 or 3 inches away from the hairline where I will glue loose hair; and any actual hairline itself, for which I will construct a little 'hairpiece'.
I am more likely to err on the side of making the handfuls of hair too thick instead of too thin. Too thick, and most of the hair will not stick in the glue, it will just come loose and make a mess. It is almost impossible to err on the side of making the handfuls too thin.
I make the rows closer together with the loose hair than I do with the wefted hair, about 1/2" apart. The loose hair has to be applied more thinly, so the rows need to be placed more closely together to cover adequately.
(First pic.) I trace the hairline with a pencil on a piece of wax paper, lay down a line of glue, and then press loose hair into the glue using a damp cotton swab. Again, if the swab starts to get too sticky, and the hair wants to stick to it instead of the glue, I throw it out and start with another. I let this dry until the glue is clear (usually overnight) and then (second pic) trim along the pencil line. After this I (third pic) very carefully peel the finished hairpiece from the wax paper, and (fourth pic) glue it in place.
After the glue has dried overnight, I comb out the loose hair (there is always a lot of loose hair, don't worry too much about any shedding at this point) and then trim and style if I so desire. I put any big hanks of trimmed hair in a ziplock baggie to save for future hairing projects, and then to tone down any shininess, I color over the dried glue on the hairline with acrylic paint or a matching Sharpie.
There it is! Any questions, please feel free to drop me a note at firstname.lastname@example.org!