Join Date: Jan 2005
i have a historical opinion on this, as apposed to a metallurgical one.
for some reason, the wootz ingots were small, maybe too small to make a large blade. and so, a blade was made from different ingots joined together. this is why some indian blades have a 'scarf/lap' weld along the blades. also, why there is normally a join along the spine of all wootz blades, where ingots have been sandwiched together.
i am away from my notes, but i believe travernier mentioned this, when travelling with the moghuls in the 17thC. he said that each ingot was always cut in half, to determine the quality of the pattern. a good size sword was made from 3-4 of these halves.
occasionally, you will find a scarf weld, with one side being wootz and he other steel. even rarer, you will find one complete side being wootz, whilst the other is steel or even pattern welding. rarest of all, is both sides wootz, but sandwiched between a layer of steel (presuming it is steel as the colour seemed different). the last is a thick blade, of substantial quality.
the joining/sandwiching/scarfwelding is my theory, not traverniers. he just mentioned about the halves. during my collecting/studying i've heard many different theories about scarf welding, some pretty ridiculous (from stregthening to religious). this is one that i feel happy with, and think that travernier adds some fuel to it.