Tortoise shell is now illegal to sell- and rightly so. Any tortoise shell items must now be described as ‘faux-tortoise shell’ to get around the embargo of selling tortoise shell items. These vintage ‘faux’ tortoise shell knitting needles are much prized by knitters and artists alike and are now very collectable. Knitters like them because they are super flexible and so much easier to work with, and artists refashion the needles into art / jewellery items- see Etsy and Pinterest for examples. Because the material is very pliable, artists use hot water to mould the needles into new shapes/patterns.
I am a knitter myself and love the way the needles work. I’ve been collecting these needles for quite a while now and have amassed a small fortune- email me with what you need and I can send you a comprehensive list of needle sizes/quantities and makers.