I have never used silk but read that Coats & Clark Rayon 40 wt thread was a good substitute I have a spool in light beige/cream color that seems to disappear into any color fabric. But, it is so fine that it's hard to keep the needle threaded! Plus you must use a needle with a very teeny, tiny eye. The label says it's for Decorative Sewing, machine stitching, topstitching and embroidery. It has a sheen. The other thread I've used with more success is Coats & Clark FINE wt Rayon thread that is polyester covered polyester. It is beige color and has no sheen. I like it best.