A hot glue gun and glue sticks are all you need to create color mixing gems. Glitter glue sticks provide a nice sparkle but any standard translucent white glue stick will do. Plug in the glue gun and give it a few minutes to heat up.
When filling the cutouts with glue, start with the glue gun tip near one edge, pointing towards an LED. Squeeze to extrude the glue towards the LED, slowly drawing the tip of the gun away as the hot glue starts to fill the cutout. At about the middle of the cutout, rotate the cuff 180 degrees underneath the tip of the gun, and move the glue gun tip to the opposite LED.
Squeeze the glue towards the other edge, moving the tip back towards the middle. When the cutout is mostly filled with hot glue, lift the glue gun up slightly and squeeze a light strip of glue across the very top of what is already extruded. Run that final light squeeze of glue from one end of the cutout to the other, allowing it to melt and create a smooth top surface. After gluing each gem, set the glue gun aside and hold the bracelet level while the glue you just applied settles and cools.
The video below demonstrates this technique.
It can take a little trial and error to find the best technique for applying the hot glue. You may find it useful to cut holes into scrap pieces of EVA foam and practice gluing those before working on the bracelet directly.
Some other useful glue application tips:
- Create each gem one at a time, and don't start the next one until the previous one has fully cooled.
- After extrusion, glue will flow a bit until it cools, so it is important to hold the hole with the molten glue horizontal until it sets.
- If a small bit of glue overflows the hole, it's easiest to remove it before the glue dries. Carefully use tip of a toothpick to scrape off any excess drips around the hole.
- If you don't like the shape of the dried glue, you can re-heat it carefully with a hair drier or hot air gun set to low heat. Be careful not to burn the EVA foam in the process. Once the glue liquefies and flows a bit, hold the "gem" level while it dries again.