I have been asked about what kind of clay I use for my original clay sculptures. I only use one type and it is a water-based clay and is perfect for latex coating. It is called WED clay… here is its promo.
“Originally developed for use in sculpting Disney’s animatronics models, WED (Walter E. Disney) clay is an extremely versatile water-based clay with properties similar to many of today’s most popular oil based clays. It’s smooth, slow drying, extremely pliable, and works great for sculptors seeking a “fast sculpt” medium. WED clay is still commonly used by professionals in the entertainment industry for masks, modeling, mockup, and large scale sculptures. Like any water based clay, WED clay needs to be kept moist, preferably with a spray bottle or a damp towel. Saran wrap is also commonly used. It is not formulated to be fired.”
I get mine from Laguna Clay, WED Clay- 25lbs. for about $30. Will come boxed in a plastic bag and you can re-use it over and over if you keep it clean and moist. Great stuff and holds details like crazy. Just remember to mist your work down and cover it with a plastic bag or saran wrap if your going to be away from it for a while. I apply my first three layers of liquid latex onto the clay very thinly while the clay is still a bit damp. When you apply latex you also creat a latex flange border around the base of your clay piece which seals it from the air, keeping it from drying out on you. When your all done with the mothermold part and dig out all your original clay from the latex mold just bag it up and spray it down good with water for storage.