The last few days I have been in Tenn. with my wife who wanted to attend the “A Mountain Quiltfest” event.
I was looking around at the many types of threads in the YLI Thread vendor booth, when the guy asked what kind of quilt thread I was looking for I told him I wasn’t looking for quilting thread but instead was looking for some kind of thread I thought might make an interesting fly tying material.
He said he sells a lot of metallic opal thread to a couple of different fly shops. One in New England the other shop in Washington or Oregon border area. YLI sells spools with hundreds of yards of the stuff, but I purchased a dog-bone card with 30 yards. I can’t match the part number on the card to a product on their website, but I think this is the same stuff. My card is labeled “Metallic-Opal” 30 yards. It is available in many other colors.
https://ylicorp.com/collections/ribbonfloss/products/ribbonfloss-metallic?variant=29211926298685
https://www.123stitch.com/item/YLI-Ribbon-Floss-Metallic-010-Opal/144-00-010
“Opal metallic YLI ribbon floss! Ribbon Floss is a soft, pliable, braided ribbon …”
Worth a try - angling the card angle to the light it does look a bit like fish scales.