Bedham's Disk..."is named after the English newspaper-man and toymaker Charles Benham, who in 1895 sold a top painted with the pattern shown. When the disk is spun, arcs of pale color, called Fechner colors or pattern-induced flicker colors (PIFCs), are visible at different places on the disk. Not everyone sees the same colors." Thanks, Wikipedia! We used 608 bearings to give it a smooth spin.
75% to add weight allowing for a longer spin
3 shells and 3 bottom layers.