Food-Safe Silicone Mold

Measure a spot in your freezer where your mold will fit, and cut a piece of foamcore to those dimensions. (My freezer has a drawer that's 15 x 11 inches.)

Cut four mold walls to match the sides of the bigger piece:
  • 2 pieces @ 4 x 15 inches
  • 2 pieces @ 4 x 11 inches
Mark each mold wall with a level line one inch from the edge. This will be your glue line-- the floor of the mold must be lifted from the table to leave space for the legs of the LEDs to poke through/splay out.

Glue up the walls of the mold box with a hot glue gun, applying extra glue at the corners and the "undercarriage" of the mold-- it must be a liquid-tight seal to prevent liquid silicone from seeping out!
Use an awl to poke starter holes for a whole bunch of 10mm LEDs. Poke the leads of the LED through the foamcore mold floor and splay the leads out on the opposite side to hold the LED tightly in position. Repeat for as many LEDs as you can fit in your mold box-- we lost count around 180, but your mold can be any size.
Place a large mixing tub on a very accurate scale and zero it out. Pour part A of your food-safe silicone into the tub, approximating the volume needed to submerge the LEDs in the mold box.

Wear rubber gloves when casting with silicone, and be sure to cover your work surface and yourself to protect against messy spills.
This food-safe silicone says to mix part A and part B in a 10:1 ratio by weight, so place a smaller mixing tub on the scale, zero it out, and pour in part B to equal 10% of part A's weight from the previous step.

Our measurements:
  • 2000g part A (tan rubber)
  • 200 g part B (red catalyst)
This stuff is harder to mix than peanut butter. Just keep mixing, and try not to encorporate too much air into the mixture by recreating scenes from Ghostbusters 2, although extremely tempting.

Scrape around the sides and bottom of the tub to make an even mixture. Only when it is all the same color is it ready to pour.
Pick a location and slowly pour in all of the silicone, scraping the sides of the tub to get it all into the mold box. Resist the urge to move the stream of pouring rubber, and rather let the silicone fill the mold box like a mudslide-- this helps avoid air pockets from forming next to the LEDs. Tilt the mold box to get the rubber to flow evenly over all the LEDs, then let the mold cure for 24 hours.
The next day, break apart the mold box and peel the silicone mold away from the LEDs and foamcore.

You can trim the edges with a craft knife or scissors. According to the food-safe silicone manufacturer's directions, we baked our finished mold for 4 hours at 212 degrees F, then washed it with regular dish soap.

The LEDs can still be used in projects, just pull them out of the foamcore!
This guide was first published on Mar 05, 2013. It was last updated on Mar 05, 2013. This page (Food-Safe Silicone Mold) was last updated on May 04, 2015.