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Making hollow beads

Hi All, I need help determining the starting size of the disc for
hollow beads. I’m planning tofabricate a round, hollow bead and quarter inches in diameter. I am very familiar with
the process of making such a bead. The only question I have is how do
you determine the size of the 24 sterling sheet one needs to form a
particular size of round bead. Can someone point me to a particular
book, or is there a formula? Thanks for all the wonderful

Mimi Grabis

From Alan Revere’s book, Professional Goldsmithing:

Disk diameter for a hemisphere = (outside diameter - wall thickness)
x 3.1415 x .92

so, if you want to make a 12 mm hemisphere from .7 mm sheet then
subtract .7 from 12 and multiply this by 3.1415 (pi) and then by .9,
divide by 2. This equals 16mm.

As Alan states in the book “the accuracy of this formula varies
according to the technique of the goldsmith applying it.” This is
because as you dap the shape it is possible to stretch the metal as
you hammer, altering the metal. Still it is as good a starting
place as you will find.

I must seriously recommend that anyone interested in goldsmithing
get Alan’s book. There is a lot of here that is both
inspiring and very handy.