I bought this object in Paris. The spiral is an Arcimedian spiral
1283. but this type of lathe had been in use for centiries before this date, and if the turner fastened a cutter to the wood part of the bow, a decorative spiral could be cut into the surface of the finished object on the machine by moving the bow backward and forward and applying preasure to the work piece. After all, turning with one hand and one foot is no mean feat, (feet? geddit?)
Peter Lu's article. If Mr Lu is correct, then ornamental turning is 2000 years older than most researchers thought. You can use the magnifying glass above right to read the article.
Here's a copy in box, on a slide and I've rolled it past a pencil held on the centre line as you can see the spiral isn't the right geometry.
On the web, An Archimedian spiral requires a (Marker) moving at a constant speed in relation to a revolving object. Please note the suggestion by Mr. Ty Kroll, ( that the marks were made whilst the object was still on the lathe that it was made on) this idea is so obviously correct that I am ashamed I didn't think of it first.
Showing the edge profile
There is a groove inside the centre hole Also note the regular spacing of the grooves, this would indicate a mechanical jig, but remember these objects are known from 7c BC.
Etc.
