You will need:
1 - a table or solid surface that can get beat up or stained and is coated or smooth (a polyurithane-sealed worktable like at TechShop works great)
2 - hot glue gun + glue
3 - mixing bucket
4 - measuring cups (2)
5 - stir stick
6 - four pieces of wood
7 - surgical gloves
8 - RTV Silicone (I suggest Smooth-On's Mold Star 30)
9 - Two-Part Urithane (I used Task 8 from Smooth-On for this application, though Smooth Cast 325 would be easier for beginner)
Step 1: Building the Mold Box
Simply cut 4 lengths of wood, longer than you need is better because you can reuse them for another larger mold box at a later time. The wood I used is pine, and it is unfinished.
Lay the wood out in a square pattern with the edges of each piece going beyond the structure as shown in the picture.
Using a hot glue gun, apply a solid bead along both bottom edges of the wood along the entire length and on the wood-to-wood joints. More glue is better than less. Hot glue peels off easily from the table and the wood.
Step 2: Mix and Pour
Place your objects in the mold box. Hot glue the bottoms to the table.
Mix 1 part A to 1 part B.
Pour evenly and from about 1 ft above the box in the center, allowing the silicone to flow over the parts. This will minimize bubbles.
Allow to sit for time prescribed (for me it was 24 hours)
Step 3: Start Casting
Mold on you crazy diamonds.