Step Three

My icicles were made to fit from the inside top of the case to the inside bottom, so I measured them larger than the case (I find it is easier to file them down later for fitting). If your shape needs to be smooth then you can use the mineral spirits and a brush to smooth the clay down.  The clay is oil based and the mineral spirits is a thinner for oil, so it works perfectly.  Try not to get the mineral spirits on your hands.

Step Four

Now lay the clay piece over something that the latex won't stick to after it dries.  This surface should probably be plastic (that's why I used a plastic bag).