I am a firm advocate of large-scale Celtic knots. I believe in Celtic knots that can be recognized and appreciated from across a room.
I used to position fabric shapes with a bit of space between them to give the illusion of a stencil to my Celtic knots. The spacing uses artistic convention and visual perception to give the illusion of woven lines.
Now, I weave flat-fabric loops together to achieve my Celtic knots.
First, I enlarge my chosen knot to use as a template.
Then, I trace each of the paths of the knot on fusible web, fuse to fabric, and cut out as separate loops.
Next, I use the printed knot as placement guide. I weave the knot from the bottom up, so I locate where the paths go “under” another path near the top of the knot and cut open the loop. I layer the bottom row of loops according to the guide, and pin through all layers (fabric and paper).
Then I weave the paths over and under each other, row by row. I pin the two layers of fabric together at each intersection, but not to the paper beneath.
The entire knot can be lifted and treated as a single unit at this point. I unpin the bottom row from the paper guide (keeping the layers of fabric together). There is no problem sliding the knot off the paper guide and into position on the background fabric.
I move the piece to my ironing table. I carefully remove all the pins. After a final check of “overs” and “unders” for each path, I fuse the knot in position. From here, I can zig-zag the raw edges, and embellish at will (possibly an embroidered design down the center of each path).