I wanted to try a mold of this relief. It was a little large for a push mold so I used two part liquid silicone. I put the relief in the bottom of a disposable aluminum pan and sealed it to the bottom using some plasticine type clay I had to minimize the mold material seepage underneath the piece. You could use polymer clay just as well, I just had the other type handy and didn’t want to contaminate my polymer clay.
That created a thin, rather flexible layer of silicone which contained all the detail but wasn’t very sturdy. So I got a slightly bigger pan and dammed up the area I wanted to fill with more plasticine. Then I mixed up some plaster of paris (try the hardware store, it’s a lot cheaper than the craft store) and poured that over the silicone to make a mother mold. The mother mold supports the silicone and keeps it from flopping. I overdid it on the plaster a bit but now I have a VERY sturdy mold 
The following shows the blue silicone mold within the plaster, once I pulled out the original piece and trimmed away the thin bits of seepage from both the plaster and silicone. This mold isn’t quite sturdy enough to be a push mold. I did try it with some Studio clay and it worked slightly but the blue silicone is too flexible to keep all the detail under pressure. It should work well with liquid casting materials though.
Final Mold and Original Relief