All I did was carve the stone mould based on the period design and I made what is probably the same mistake that the original mould maker did, in that neither are quite symmetrical, simple though that is to do when you have a ruler. Maybe he didn’t have a ruler and compass and protractor. All I used was a ruler to measure the lengths of the sides and width, but didn’t concern myself with getting the angles precisely correct, and unsurprisingly the result was not symmetrical.
Here is a photograph of the belt spangles:
Here are the Museum of London Dress Accessories book drawings:
Also a side view of the left hand one:
Note that I need to carve the decorative bumps deeper. What I also realised though is that the bump that is almost outside the diamond shape just kind of happens if your hand slips slightly when trying to drill such a hole (by twisting a pointed iron tool around in your fingers). The side view also shows how thin a casting you can get by using a stone mould.
Here it is, the face part of a three part mould:
I have deduced from the ridges on finds that a three part mould is what was used for many of these things. Now all I need to do is carve moulds for a dozen or two more, to have some variety.