bulldog,

My guns are in storage so can't get a photo but
here's a description.

On an English foresight you often have a small Brass bead on the foresight which I and other file down at an angle so that the light reflection is the same regardless of where the sun is.
(A round call of Brass or a dead flat (as in vertical) piece of Brass
will change the POI as the light reflection changes even if you do everything the same).

All a Diamond sight is is a small diamond INSET into the point of the foresight so that it shines white from the light reflection and
as I described above, if done correctly you get the same sight picture / light reflection all of the time.

You don't need to use an Expensive Diamond.

Hope this helps.

500 Nitro