Sturdy concrete pots and beautifully marbled stone plaster bowls can be used both inside and out. METHOD: You need plastic pots and plastic buckets that you do not particularly care about. Plastic is great for casting because it can be softened up with warm water when it's time to loosen the mould. Blend the plaster and concrete according to the instructions on the package. To create the marbled effect in the plaster, scrape some paint off a paint cake and stir. Pour into the larger buckets and bowls and shake to get rid of air bubbles. Press in a smaller bowl or bucket and fill with something heavy, like water or stones. Tip! The object used to cast concrete should be brushed with cooking oil beforehand to make it easier to remove. This also applies to the object lowered into the concrete.