Once upon a time linen or hemp was pretty common for all kinds of work. And it was pretty good stuff. My wife spins and I've seen raw flax that has individual fibers that were 36" long. The longer the "staple" (the fibers) the better the thread that will be made will hold up and the stronger it will be.
Since WWI probably the quality of linen has fallen with each passing year. About 4-5 years ago, The last of the most famous and reliable Irish linen mills closed down. But before that, linen yarn coming from even the best of those mills was comprised of fibers that were seldom over three inches long. Lots of reason for this but mechanization had a lot to do with it in one way or the other.
The upshot is that the linen yarn was not strong. Not Tradition strong.
Shoemakers Traditionally twisted together 8-10 stands of #10 linen yarn to create an inseaming thread. It was waxed with pine pitch and pine tar ameliorated with cod or whale oil and beeswax. Most of these ingredients were widely available during the age of tall ships and, in fact, the last company to produce pine pitch in the US was Rausch Naval Yards in Louisiana.
The wax was used to not only protect the thread (which is organic after all) from the beasties that live on the foot and in the shoe, but to seal the holes in the insole that the thread passed through--the wax heating up when pulled through the holes and solidifying again as it cooled.. And it was tremendously sticky and once the stitch was tightened it was damn near impossible to pull out.
Good linen yarn is not readily available anymore. I have boxes of it from before WWII and I hoard it.
In recent years shoemakers--from the factory to the bespoke maker have had to look for new materials. Dacron has emerged as a relatively viable alternative--it doesn't stretch as much as nylon but it is admittedly not as "tight" (unyielding) as linen or hemp.
I use dacron thread instead of linen for my inseam. It is available. It is immensely strong. It won't rot.
I switched about 15 years ago...after an eye-opening series of events with a pair of boots I made for a farrier (horse-shoer). And, as with the split bristle technique, have been instrumental in helping to evolve and promulgate this procedure.
The drawback is that it doesn't hold the wax near as well as the linen (although some recipes for wax work better than others) but to counter-balance that, it doesn't need the anti-bacterial properties of the wax either. And if a stitch is given a "twist" as it is pulled tight, the locking properties of the wax will be more than sufficient for the purpose.
So...I tell you all this because, as with the boar's bristle / nylon bristle conundrum, the materials may have changed (out of pure and unadulterated necessity) but the techniques are still valid and unimpeachable.
Some way had to be devised to preserve the Traditions as much as possible.
I'll post some photos and another video link later this evening...after I get back from walking the dog.
Edited by DWFII - 1/20/14 at 4:23pm