Mold Keys:
Once you have your clay all set up the next thing to do is add mold keys. Mold keys are important because once you close your mold everything needs to line up perfectly. Your mold keys must all be going in the same direction even if the mold surface is not. You can see on the picture to the left that all the key holes are going straight up and down even in places where the mold is at a slant (like on the left leg). This is important because you need to be able to close this mold, and if the keys are going in different directions it would be very tricky to close. For my key holes I used the back of my brush and pushed it into the clay about 1/4 of an inch. The key holes are relatively close to the sculpture so that the parting lines by the sculptures edge line up perfectly on the finished mold.

Adding Your Mold Walls:
You can build up your mold walls with clay if you wish, but I like my molds to be very clean with hard edges. I used aluminum roofing sheeting (found at any hardware store- sold by the roll) for my mold walls. Aluminum sheeting is very easy to cut and bend into any shape that you may need. You can see on the picture to the right that I created 2 pieces from the sheeting and attached the pieces with hot glue. I pushed the sheeting down into the clay very carefully so as to not warp my clay lay-up or mold keys. You can also see that the bottom piece of sheeting is very snug up against the base of the sculpture. I will be casting this sculpt by pouring into the base of the sculpture and I need that part of the mold to be open. Once my mold walls were all set up, I lightly sprayed the clay with crystal clear. Once I pour this side of the mold and the silicone sets I am going to remove the clay, and sealing it helps. Before moving on to the silicone pour- double check everything. Check all around your sculpt and make sure that the clay lay-up is right up against your sculpture and is clean. Check that your mold keys are all straight up and down. Check your sculpture and all its detail and be sure it is clean and clear of any clay residue. Finally, wrap all your clay on the outside of the mold with saran wrap so that it doesn't dry. All this clay will be removed later and trust me, you do not want to be removing hard clay (unless your some kind of sadist that is). If everything checks out then move on to the next step; this is your last chance to fix anything before it becomes permanent (in silicone).