I have my Uranium spider, and that's the only one I want, Keith.
The paperweightiness of it is a minus point, (I don't collect pwts) but the uranium and the spider are two major plus points I could not resist.
In Hajdamach, 20th Century British Glass, p.379, the caption to plate 806, (a photograph of these weights) reads;
"Cased, cut and engraved weights by Webb Corbett from the mid-1970s. Designed by David Smith, the work's designer, the weights were only made for a short period of time."
Shame we don't know exactly how short.