Step 1. Using the wooden strips, make a box around the glass plate. Seal off the edges using the window cement. Make sure everything is air tight.
Step 2. Place your record inside the box making sure that the portion to be copied is facing upward. Squeeze in some window cement to mark where the hole in the record is.
Step 3. Mix the silicone (Smooth On OOMOO 30 or OOMOO 25) for about 3 minutes before pouring in to the mold.
Read more: http://gadgets.qj.net/How-to-Pirate-a-Vinyl-Record/pg/49/aid/39381 (via DIY Happy)