Here are some photos of an ivory sight I am making for a pistol in the works. I start by making a tapered slot in a piece of .050" thick steel. I then file a slight draft in the slot making the underside of the slot slightly larget then the top side. The draft is the key to locking the ivory insert into place. Then I fit a piece of ivory from the underside being careful to match both the taper and the draft. Once I have the ivory insert fit into the slot I file the underside of the ivory flush with the underside of the base. Once the sight is tapped into the dovetail on the barrel the ivory insert is locked between the barrel and the sight base. I have used this design on several rifles and pistols and have not experienced any loosening of the blade from the base. I do keep the blade rather shallow to avoid breakage.
DMR
Top view of sight looking straight down
Underside view of sight
Top view of the sight base and the ivory insert separated
Side view of the unassembled ivory insert and sight base
The ivory insert being pushed up through the bottom
The ivory insert completely installed into the steel base and ready for installation into a dovetail
Sight installed on an Ed Rayl brass pistol barrel