This is the pattern I'm referring to.
Table Mat that is crocheted in 3/4 inch medallions that will form a finished piece that is 20 inches square. It calls for an obsolete thread that was called Dritz Luxury Belastraw. Most of the patterns in magazines also appeared in pattern books and I'm making a guess this one would have appeared in Table Mats & Doilies of Dritz Belastraw - Vol 23 from 1951
(Picture used with permission from Cheryl12108)
Dritz Belastraw was a 100% Viscose Process Rayon thread, 5 ply, that was distributed by John Dritz & Sons (now Prym-Dritz Corp). The thread is reported to be a bit like a soft nylon straw and was fashioned for making of bags and hats. It's was a strong thread that was worked tightly. The fibers were prone to stretching when wet, and dry cleaning was sometimes recommended in the pattern books.
And, that's all I've been able to find. In looking at the pattern, I'd say it's an easy medallion design that would be quite delightful in a number of heavier threads. I've listed it in the shop as a Free Download, should you be interested in giving it a try. (If so, I'd really appreciate your reporting back as to which threads you used !).
Okay, back to work.
Thanks for dropping by,