but I can't find any images. It seems as though I have seen them before!
Interesting that you should mention ojime. As a specialist in ojime for forty years, I feel I should say: Most likely these are Chinese beads used to punctuate tassels on the corners of folding card tables. Black silk table covers were used in the the early 20th Century for mahjong and bridge parties. Often, I ran into them in the seventies. Dealers and collectors often used them to fill in their "Ojime Collector Necklace". And this type of substitute is commonly referred to as an "Ojime."
To be scholarly, a person may insist that an ojime should be: #1. Japanese #2. Made specifically for usage as a slide closure on an into or tobacco pouch—as this is the literal translation for the Japanese word ojime: Slide Closure. -Therefore, it could be argued: an ojime is an accessory to clothing with functional usage, and not a "bead" as we usually think of it.
The HASTY assumption is: It is an ojime because it is 3/4 inch in diameter and has a large aperture. But this glass appears to be more likely Chinese, not Japanese. And, I feel that if finding them in a group of four, it could be a clue -although not evidence- that these were made for usage on the corners of table covers.
