Kylo Ren’s lightsaber has a particular look in The Force Awakens — it’s raw and fiery. We’ve shown how others have modified blades with hot glue to capture the effect, and Redditor Salok9755 used silicone gel to transform a FX blade. You should practice this technique with something less expensive before you dive in. Salok9755 explained:

liberal application of $6 clear silicone gel from the plumbing department at home depot. It dries pretty quick, so once the surface was completely covered it was pretty easy to shape by hand. Then 4 VERY thin coats of transparent red model spray paint (2 coats each of 2 colors, alternating). And primer and sealer obviously. Took about 10 days start to finish, but the vast majority of that time was drying/waiting. Maybe about 45 minutes of actual work, and roughly $30 in materials

via Reddit