Incorporating powdered graphite into your pencil art allows for faster application of dark tones and soft blending effects.
It can be tedious doing large areas of uniform pencil shading; I've found that powdered graphite provides a useful shortcut, and can yield some interesting results that would be hard to achieve with pencil alone. For this tutorial, I've documented the process I used for the pencil/powdered graphite underdrawing for my digital painting Full Blooded - an 11x14 piece with a lot of solid blacks that I was dreading having to build up by hand.
Some general tips for working with powdered graphite:
1) Sketch in the outlines. You'll lose a lot of these in the shading process, so don't put too much time and energy into them - just give yourself a general guide to work with. I'm using a lightbox, and have my original sketch taped to the back of my working surface to limit the amount of invention I need to do. Mask off any areas (borders, important details) that need to be absolutely white. Sprinkle a tiny amount of graphite (really tiny - like less than 1/8 teaspoon) over your dark areas.
2) Use the edge of an index card to gently push the graphite around the paper for even coverage. Note that your "brushstrokes" will show, so you'll want to be consistent in the direction and angle you push the graphite. Here, I'm working in vertical lines.
3) Tap off the excess graphite, and use a large soft brush to brush away any residual powder. At this point, you can use a tissue or paper towel to rub the graphite into the paper and soften the directional strokes left by the index card. Note that your color is going to be a little bit blotchy at this stage - you just want to make sure that there are no extreme dark or light areas.
4) Use a soft pencil (a 5B shown here) to shade in the darkest tones of your sketch. I know, you thought you wouldn't have to do any pencil shading with this method. Bummer. Fortunately, you can do a pretty rough job here - the layer of graphite already on the paper makes the surface a little bit slippery, and rough pencil strokes won't cling to the paper the way they would if you applied them to a clean sheet. Just darken things up a little, keeping the direction of your lines more or less consistent.
5) Use a tissue to soften the pencil shading and blend it around the paper.
6) With a kneaded eraser, start to pick out the light areas of your drawing. If you pick up too much graphite and get a harsh white area you didn't want, you can blend in the surrounding graphite with a tissue.
7) Go back in with the pencil of your choice (I used the 5B again, along with an HB mechanical pencil for the sharp details) and start drawing in the shapes and edges of the final image.
8) Continue around the image in the same way - pulling out the lights with a kneaded eraser, and deepening the dark areas with pencil. As you can see, although I only applied the graphite powder to the upper third of the image, over the course of working on the drawing a thin layer of graphite has migrated all the way down the page, leaving an even, light overall tone to work from.
This probably looks like almost as much work as doing it all in pencil, but you'll have to take my word for it that it's quite a bit easier, less time consuming, and the results are generally better looking. I also like the softer effect that the powdered graphite gives, and how forgiving and reworkable it is compared to heavy pencil shading, which tends to gouge and flatten the surface of the paper.
While powdered graphite has its limitations (it's generally better suited for hazy shading rather than crisp, clean lines) I've found it to be a handy tool for expanding the value range normally achievable with pencils.
For more in-depth information on my painting process, check out my tutorials on Patreon.