they did it was a secret that died with them...
...There's a scattering of people around the world today, however, who have come up with their own methods to create art with these intricate, glass-caged algae. Diatoms are as small as 5 microns, so one entire star shapes from this design would be smaller than a period in newspaper print! [Above, an Arachnoidiscus and other stylized diatoms, with details from their valve faces and girdle bands]