I’ve tried different two-part mold putties and Silicone Plastique by Make Your Own Molds is my clear favorite. I like it because it’s workable for 15-20 minutes.
To get the edges of my mold level and butted up to my object, I need more workable time than the three minutes you get with other mold putties. Fast-curing putties are good for things like leaves or textures where butting edges cleanly up to your object isn’t an issue.
It takes 60-75 minutes at room temperature (70˚F) to completely cure.
If you have an area of your mold that’s too thin, you can add more putty to it after it’s cured and it will stick rather than be repelled. You can bake polymer in it too. It’s great stuff.
Polymer Clay Journey 