Continuing on with the kintsugi idea I went off to make a wooden frame for the foundry sand to sit in with a wood lid to press down the pewter. Hopefully this will solve the issues with directing the pewter in the right direction and also having the pewter refrain from pooling on top of the glass itself.
Using the wooden frame I made and the foundry sand I pressed my chosen glass pieces into the sand making sure that they were all equal on the top. When pouring the pewter I had to be quick and for the first few times that was very difficult to do having only 2 hands, but once I got the hang of it I managed to start producing acceptable casts. My only issue was that the pewter was still pouring over the glass and did not remain clear. I think the only way to successfully do that is by making a mould tailored for each pendant which would be a lot of work and would be a lot of waste of plaster/vinamould. I think this process is not the best for my pieces, I will need to return back to the drawing board and experiment more. Bellow is a few outcomes which worked reasonably well.