Which ends are the free ends?
I have not shown the free ends, and I have not mentioned anything about this, on purpose !
I had hoped that somebody would ask, and that this would offer me the opportunity to comment on the issue.
I have a theory, which I have repeated a number of times, but which I was not able to submit to the revealing, and relieving oftentimes, torture of the experiment : I think that the defence against slippage should be arranged as a defence against the enemies ( the tensile forces ) coming from outside with their full power ( from the Standing End, loaded with the 100% of the total load ), towards their final destination, where they would, hopefully, be totally absorbed ( to the Tail End, where the load would be diminished to 0%, otherwise the knot would slip ). As anybody who has visited a medieval castle knows, the defence is gradual, arranged in steps, the next harder to be outflanked than the previous one (1). This way, even under a lighter than the maximum loading, there would be fewer or no parts of the Standing part which would not be tensioned / which would remain slack, so, most of the time, almost no the part of the tighten knot will not contribute in the absorption of the tensile forces.
If we have this theory in mind, we can distinguish the Standing from the Tail ends in a glance. Which ends are nipped more efficiently as they come out of the knot ? Those are the Tails.
There is a yet another theory, which also has been neither proved nor disproved by experiments : We use to say that the continuations of the Standing ends should enter into the core of the knot s nub following curves as wide / smooth as possible. So, we try to make the paths of the Standing parts as gradually bending towards the centre of the knot as possible. So, in this bend, which ends follow wide paths as they enter into the nub ? Those are the Standing ends.
Now, do I KNOW that this way of loading the bend would result in a less slippery and less weak knot ? Noope !
Who knows how this knot will "fold", when it will tied on a most slippery material...Who knows where the "weak link" of the knot will be, and where the line will break...
So, all that I can do for the time being, is to wait patiently for the brave knot tyer who will test all the simple knots, to test this bend, too, in its "normal" AND in its reversed form. On ordinary materials and moderate loads, there was no slippage, and, of course, no breakage.
1.
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