When the resin has set up to the consistency of firm rubber but not completely hard it is time to de-mold. Begin by peeling off the duct tape. Then work around the mold loosening the edges. When you have the edge loose all around slowly pry it apart until it pops loose. Then while the resin is still rubbery use scissors to trim the lip off of the edge. Now let the resin harden up the rest of the way, about an hour. After it is completely hardened clean the residual clay off.