Abstract: A kit for preparing a cured article may include first and second casting compositions configured to form a curable composition, and an additive delivery composition for introducing an additive into the curable composition. The additive delivery composition includes a liquid carrier and at least one additive. The liquid carrier may include one or more of polyvinyl acetate, polyvinyl alcohol, or polyacrylate. A mold assembly for preparing a cured article may include a first mold body defining a first mold chamber and a groove surrounding the first mold chamber. The mold assembly further includes a second mold body defining a second mold chamber and a tongue surrounding the second mold chamber. The tongue is receivable into the groove to secure the first and second mold bodies. The first and second mold chambers together define a mold volume configured to receive and shape the curable composition.