One of the things about using oil based clays is that they need to be heated up a bit to help block out sculptures so you’re able to build up thickness quickly that you can then manipulate to create your piece. 

a popular way of heating the clay for you is to use a heat lamp above whatever container you have your clay in,

I’ve found that using a crock pot is the one-stop fix for this.   you’re able to heat all the clay evenly to a molten liquid you can pour, you can put it on a medium setting so its the consistency of peanut butter.

another thing i like about doing this is that when I’m done making a stone mold, there’s usually pieces of plaster or some dirt or something on my armature when i go to remove the clay, heating it up super hot can make all the bits and pieces separate so i can skim the junk off my clay and i can either re pour the liquid clay into smaller blocks or just let it cool and keep it in the pot