Your Celtic work should not be difficult. When I made several blocks, I believe that I drew the design onto the background cloth with pencil, for a placement guide. I used sequin pins to pin both edges of the bias tape. I also did not run the entire bias under one that was placed over it. I trimmed, and started again, to lessen the bulk.
I have several good books on how to do Celtic knotwork, and how to design it. I remember that it was a lot of fun, but haven't done anything like that recently. I did find the (Dritz brand?) bias tape maker to be an invaluable resource.
Good luck!
Patricia Cummings
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