Bad edges can be often discovered even before the weaver started the warping. If the warp is planned too economically, with too few ends per inch, there is quite a chance that the edges are already doomed. An open warp means plentyu of take-up on the weft, which pulls in the edges. If we do not compensate for this the warp ends will lie much closer at the edges than elsewhere. if we do compensate-- i.e. leave enough weft in each shed to oversome the pulling action, we must weave much slower, and the edge will be uneven. Thus when planning let us not be too stingy about the number of of warp ends. A little more time spendnt on threading will pay dividens once the weaving started.
Then, when warping and beaming, care should be taken to have an even tension of the warp all across its width. If anything - it can be a shate tighter at the edges, just the last few ends. The same applies to the typing-in: make the first and last bight (strand of warp) smaller and tighter. This is because there is always less take-up on the warp at the edges, and unless we are careful the edges will become flabby, or we shall have to resort to the objectionable remedy of pulling in the edges.
. . .
The tension of the warp should be as low as possible, i.e. just sufficient to get a clear shed. If it is
much higher, the warp edns at the endges will be pulled together too much, althought the edges will be
straight. In any case the tension must be always the same. Since the tension increases during weaving, the
best remedy is to move the warp forward very often - every 2 inches are so.
--Stanislaw Zielinski, Master Weaver, October, 1952, pp. 2-4.
NOTE: The last paragraph may conflict with other, more recent, teachings you may have come across. This is the first time I have read this advice (and I read a lot!), but I am certainly going to try it with my next project.