Denis Diderot published an Encyclopedie in France in 1751 with plates in 1772 showing how many of the materials used in the decorative arts were made. There were detailed drawings of the machines and set ups - often exploded so you could see the separate parts. This particular one is the gimp machine, a version of a 'rope walk' to make multi-ply cords. The core of the gimp is rotated using the wheel with one end tied to a rotating hook. The covering silk is on spools that are held on a frame on the man's belt (right hand side). He collected the strands of the silk in his hand and wraps them around a small iron bar that keeps them spread. He connects the ends of the strands to one end of the core and the rotation begins as he walks along it, the silk covering the core. You can do a few meters this way at a time.
|Illustration from Diderot's Encyclopedie (1751)
In the more modern photo, you can see the frame on a leather belt and the iron bar in the hand with the strands of silk wrapped around it to keep them from twisting as they cover the core.
There is a YouTube video of this process happening below. It is about half way through the video. The first part of it concerns winding the silk onto the bobbins that will go on the belt and the last part shows him taking the silk gimps he makes and weaving a trim. This particular business uses the trims as fashion accessories.
Now that your mind is blown that people would still make silk gimps this way - imagine that the belt holds silk covered wire and that it is wrapped around a wire that can be slipped out of the center. Now you have a silk wrapped purl. And yes, a person walks all the way along the length of the the "rope walk" as they call it to wrap your silk wrapped purls with that on their belt. You now see how our #4 purls are made.
Larger purls like the #8 can be made this way or on a spinning wheel. In the case of the spinning wheel the length is limited to about 12". Here you can see Dot at Benton and Johnson making a metal bullion by this method.
The most modern way of making silk purls is just a tiny bit more mechanized and uses a electric motor versus her hand cranking and uses a very short needle instead of a long one. The wraps of the silk wrapped purl fall off the end of the needle into a trough as it is made and can be just over one meter long. A person can monitor a few of them being made at once - so that is the big advance!
Now I think you really understand why silk wrapped purls cost what they do and why they are so hard to keep in stock!
(Sorry for a lapse in this story, my extra blogging time was taken up with family stuff.)