Acrylic polymers such as Lucite are designed to harden into hard, clear or translucent plastic. As two-part polymers go, it has a very low ratio of hardener to resin; usually several drops is enough to harden an ounce of resin. Because acrylic resins form very hard plastics, it is best to mould them in flexible moulds made of RTV silicone or other rubber compounds.
Fill the mould with water, then pour the water into the measuring cup, and note the amount of water in ounces. This is the amount of resin that will be needed to fill the mould. Also, measure the maximum depth of the mould in inches with the ruler. Check the depth and volume of the mould against the instructions for the acrylic resin to see how many drops of hardener you'll have to use per ounce to harden the acrylic. Dry the mould and the measuring cup thoroughly.
Apply a coat of mould release to the inside of the mould, as per manufacturer's instructions. Some moulds do not require a mould release for acrylic resins; check the recommendations of the mould manufacturer.
Pour the amount of resin you need to fill the mould into a mixing container, and add the number of drops of hardener recommended by the manufacturer. Mix the hardener into the resin thoroughly.
Pour the resin/hardener mix into the moulds. Allow the acrylic to completely harden; this usually takes between three and 12 hours.
Pull the mould carefully away from the hardened acrylic, taking care not to rip or tear the mould.
Embed objects in acrylic by pouring the mould half-full of resin mixed with hardener, and then allowing it to gel (which usually takes about 20 minutes). Set the object in the gelled acrylic, and cover it with a fresh batch of resin. When the acrylic hardens, the object will be suspended in clear plastic. If you want a jewel-like translucent colour to the acrylic, check into acrylic-compatible transparent dyes and add them during the mixing stage.
Acrylic casting resins are relatively safe to use, but they can irritate the skin when in prolonged contact.