On a technical point, the overlay colouring was done using powdered glass rather than a gathered / blown overlay cup method. This is the reason for the "fuzzy" edges of the yellow and white where it was cut through on the base.
Although this method of overlay is generally not as skillful or as good to look at as the cup method, it is how Paul Ysart made his overlay weights, which are a) very rare and b) very expensive to buy!