Found an online image of a Coptic wool bag in språng at the Visual Arts Data Service website, http://www.vads.ac.uk/large.php?uid=32261&sos=4. Going by Collingwood's book, the two-toned patterned area is probably worked in double cloth, creating patterns in colour where the strands swap places between the two layers. The red edges are probably worked in a single layer of cloth.
The piece is more intact than the piece Collingwood included in his book's plates, and it's in colour. Collingwood's book is in black and white.