Treble corded Brussels stitch
Treble Corded Brussels Stitch is a needlelace stitch consisting of detached butthonhole stitches worked over a pre-existing outline. It is similar to double corded Brussels stitch, but three buttonhole stitches are worked instead of two.
Treble corded Brussels stitch is attached to the background fabric only at the edges. In the example below, a simple back stitch outline is used, but this could be a cordonnet when making a needlelace slip.
For more background see the entry for single corded Brussels stitch.
Work three buttonhole stitches at the top left-hand corner of the shape and leave a gap between the two triple buttonhole stitches as for Treble Brussels stitch.
Pull the thread through to form a cord going across the shape as you do in Single Corded Brussels Stitch and Double Corded Brussels Stitch. Whip down the left-hand side edge to bring the needle just below the cord.
Work another row of triple buttonhole stitches from left to right, passing the needle through the loops between the two triple buttonhole stiches of the previous row and the cord.
On the final row, pass the needle through the loop, the cord and the bottom outer edge.
Structure of stitch
Alexandra Stillwell, Cassell illustrated dictionary of lacemaking (1996) , p.130-1