I learned to cast ceramic mold's many years ago, my first experience was 2 gallons of earthenware slip running through a ceramic mold..all over my garage floor reason being a lady told me she used old panty hose. I use rubber bands, new ones the most important reason is a tight mold. A tight mold saves cleaning time on greenware. I keep my molds clean and dry, they will produce lots of castings if you do this. I rotate also so that they don't get the fuzzies. First band your mold with good rubber bands or straps, make sure you have enough slip to fill mold. I sift my slip to get the lumps out and mix well. I leave the slip in the mold from about 10 minutes to 25 minutes. The time depends the size of the mold, the slip and the weather, I check the thickness about 3/8" of an inch thick and then dump the mold. I keep the molds out of the sun to prevent cracking and uneven drying. Molds like the African Violet Pots or something with a lid need to be dryed together...insert in base etc. I trim the mold before removing, this depends on the mold also. I dry them on wooden shelves, the minimum drying time in warm weather is about 3 days. Then the greenware can be prepared for finishing. Casting molds is a art and hard work. With handcrafted ceramics you must have patience and vision.