TamEva Le Fay had the right idea about staying away from glycerin and mineral oil... that's what they put in strippers, LOL, you might want to steer clear of those.
Sometimes, there are folks whose hair won't take dye deposits well because their hair is more slick and straight-cuticled (less porous) than most others. It's usually people with straight glossy hair who have the most problems with this.
A very old trick hollywood starlets used to do back in the 1950's to get hair dye to stick better was to open the hair shaft a little bit by rinsing with an alkaline solution... several tablespoons of baking soda in warm water the night before. I suppose that this is what raises the cuticles and allows more of the dye molecules to penetrate the shaft. From what I understand, much of black hair dye is composed of red and blue dye molecules, which are the hardest to get stuck inside the hair shaft due to their size.
I personally subscribe to the two step Henna + Indigo process. That ish is so permanent, it does not budge one iota from day one to day 1001. I only touch up my roots, and there is no color difference from root too tip. Some of my oldest hairs have "hen-digo" from seven years ago, and the color is still crisp. Some of you may want to try that, if you've become exhausted with trying to find the perfect black chemical dye.