Okay, perhaps everybody else has already come across this idea and I’m just behind the times (wouldn’t be the first time!); or perhaps it’s just because I work on a smaller scale than the majority of tapestry weavers and it wouldn’t work for larger pieces. Anyway, I had this idea, tried it out, and was SO impressed that it worked brilliantly!
Anyway, once you have finished weaving, here’s what you do:
1. Tie off all the warp threads into tassles. It doesn’t matter if they’re looped or not.
2. Take a piece of hessian AT LEAST the same size as your weaving. If using a larger piece, centre your weaving aginst it, so that there is an even border (or as you prefer).
3. Once you have lined up your weaving, use a needle to prod or thread the top left tassle through the hole in the hessian ‘grid’ that aligns with the top left corner of your weaving (before tassles begin).
4. Pull the tassle so that the knot pops through to the reverse side of the hessian.
5. Re-align your weaving, laying it flat against the hessian, and working along the row where your first tassle is pushed through, use your needle to prod/thread the next tassle through the hessian (and the next, etc).
That’s it.

The knots from the tassles provide sufficient resistance that they will not slide back through the holes in the hessian. Of course, it my take trial and error to ascertain what thickness of warp thread can work with what gauge hessian. If unsure, try knotting different thicknesses of warp thread and push them through different gauges of hessian until you find the right match. (Do this before warping your loom!)
Depending on the weight of your weaving and/or your preference re appearance of the finished piece, you may want to push the bottom row of tassles through the hessian, also. This will alleviate pressure on the top row, and prevent gradual slippage. If you prod in the lower tassles, make sure your weaving is lain flat against the hessian as you ascertain which row to prod through. The weaving will bow forward if you prod the lower row in too high. The hessian will rumple and not lie flat if too low.
You may want to add a few discrete stitches down the reverse of the sides of your weaving, giving the hessian greater support, and preventing bowing. This is also an alternative way to prevent gradual slippage of the top row of prodded tassles, and would facilitate use of the technique for larger pieces.
Once tassles are prodded through, your weaving will have a lovely rustic border/backing, and can be mounted on rod or in frame as preferred.
Although I have lots of background in embroidery, actual practical sewing terrifies me. I also get put off working pieces if I know the finishing processes will be slow and tedious. In addition, I don’t really want all of my work bordered with tassles. All in all, I’m very pleased to have discovered hessian backing!