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This process is called curing. Only cure the mold once you have added all of the layers necessary. When cured, the latex will be unable to bond with subsequent layers. It will also be more resilient to environmental things (water, air, etc.). The latex should be very durable and can be peeled right back inside-out. Then just pop it back to it's original shape. If you have an intricate object, you may have to pull and stretch some parts of the mold to release it. Be careful not to tear the mold or break your original object when separating the two. For most items, it is best to support the mold just under the flange so that it is suspended. Larger items may require extra support such as a wooden box to keep it in the proper shape when filled. You can also use a medium like sand to reinforce the mold all over. By placing your mold in sand, the weight of the casting material is supported evenly by the sand. This holds the mold in place and prevents stretching and deforming. Be careful not to get sand into your resin or plaster. Plaster of Paris is probably the easiest. It can be painted later. That said, polyester resin or similar polymers will reproduce very fine details in your item. Choose your casting medium to fit your needs.
Allow the mold to dry overnight or longer once complete. Peel off the mold. Build a support stand for the mold. Cast your item using any casting medium.