i'd think bricks/blocks would be easy enough. you could just use tupperware, or even those plastic containers that lunch meat comes in. Fill them, let them freeze, than poor a little warm water on the outside to release from mold, easy enough, just big ice cubes. If you want something intricate, You could buy two part silicone and make your own silicone molds as well, provided you have something to use as a template for the mold
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