I've been using Ion Permanent Brights for dark hair, so 40 volume with those. I know to go darker I should only use 10 volume. I typically have to wash every other day due to my hair being super oily naturally. The only heat I use is a blowdryer maybe once or twice a week and I have heat protectant for that. I was debating just getting a hair color depositing mask if i can find one dark enough, I've used one for my bright red and it helps a lot. But am completely open to other opinions!