Tiffany & Co. introduced the Tiffany Setting in 1886. Six slender prongs raised a round brilliant above the band, showed more of the diamond and made the solitaire itself the design.
What changed
Many nineteenth-century rings held stones low in bezels or heavier mountings. The Tiffany design reduced the visible metal around the diamond and opened the side view. The eye meets the stone first, then the narrow band and small crown of prongs.
Tiffany manufacture and Tiffany-style mountings
The Tiffany Setting is a named Tiffany & Co. design. “Tiffany-style” is often used for any raised six-prong solitaire. For a signed ring, verify the documentation, signatures and serial details with the right specialist.
Why six prongs still work
Six contact points can secure a round diamond while leaving much of the girdle visible. The result still depends on prong thickness, seat depth, head construction and workmanship. Worn or uneven prongs need attention.
Using the design with an antique diamond
An old European or old mine diamond may have an irregular outline, thin girdle or deep culet. Build or adjust the head to fit the actual girdle and pavilion.
If the original mounting is historically important, replacing it with a modern solitaire also changes the object. Security and preservation should be considered together.
Source
Tiffany & Co.'s official heritage timeline records the six-prong Tiffany Setting in 1886.