610 is a dark blue from the Au Ver à Soie Trebizond range: a pure silk cord made of 3 twisted plies, 40% thicker than Soie Perlée, sized between a #3 and a #5 pearl cotton. Very round and highly lustrous, it covers well and is strong: it is designed for tent stitch on 13 or 18 mesh canvas, and is also used for embroidery and sewing.
Before stitching, pull the thread through your fingers to relax it, and keep the eye of the needle facing you as you stitch to prevent untwisting. Photographs do not always match the real colour.