One of the most common sensations of lack of contrast in graphite drawings is low contrast. Because graphite is basically gray, finding the most ideal drawing tool for highlighting the darkest shadows is no longer easy for several reasons.
I've been experimenting for years. The darkest is the charcoal pencil, really black. However, as soon as we blur a little, it loses the depth of tone. In addition, it is not possible to draw with it on the already applied graphite surface, so the areas intended for the darkest parts must be omitted in advance so that we can draw with it in the end.
Black crayons are harder than charcoal, making them more ideal for drawing thin black lines (such as the base of lashes). As their binder is typically an oil, it can no longer be completely scraped back. Therefore, we use it only at the very end, to increase the contrast. Depending on the quality, they are able to cover the already applied graphite layers in different ways, so it doesn't matter what brand you choose.
I recommend two types of each black color for use:
One is the Faber-Castell Polychrome artist's color pencil, which is oil-based, and the other is the Luminance artist's pencil, which is uniquely wax-based.
If you're looking for the best, choose Lumunance, but it's often a shortage. Faber-Castell is also a perfect choice.
If you've used another type before, you'll feel the difference.