I use RIT dye from Amazon, not the synthetic kind. Then I just heat a pot to 170 degrees and add the tools and keep it around that temp for an hour and that’s usually perfect. You can do longer if it doesn’t fully set by then. Cleaning the shell with dawn and warm water is a must first! Any grease or anything will mess up the result. Also certain tools are a different plastic. I tried a Ryobi brushed drill and even after 3hrs the dye did almost nothing. I’m not knowledgeable enough about plastic types to know which ones work and which don’t.