You’re the freaking bees knees for posting this! Sitting here trying to use that same dye kit and your video was a perfectly presented walkthrough of the process & results.
They have dyes for natural fibers and you don't have to heat your fabric. I use Procion. You soak the fabric in Soda ash first, then you can dye it, even use ice if you want.
My shirt is a blend of fabric. I heard if you have cotton add salt and if you have synthetic or silk add vinegar. So if its 68%cotton 28% synthetic 4% spandex should I just mix salt and vinegar in?
The rit dye comes in a 8oz bottle or a 1/8 oz box and yes that s all you need just the dye sometimes you don't need vinegar or hot water I've used just cold or warm water and it's worked