Being able to draw a sphere puts you on the path to drawing more complex images, such as an egg or a human head. Drawing a realistic sphere can be done in successive steps as you perfect your shading technique so the colors blend from light to dark. Employ zigzag drawing to rough out your image before adding the finishing touches.
Draw a freehand circle. The more often you draw freehand circles by eye, the easier it gets. It doesn't need to be perfect or have a smooth, exact outline.
Decide which direction the light's coming from. Draw a flattened oval for the shadow going off at an angle, and lightly draw a smaller circle on the face of the future sphere. If you look at a ball on the floor with a strong light to one side, you can see the spot of highlight falls opposite the direction of the shadow. If you had more than one object in the drawing, the light would have to be the same on everything to be realistic.
Sketch in the core shadow on the sphere. Look for it when you draw from real eggs or balls. The core shadow does not go right to the edge of the sphere on the dark side. It curves around and either forms a crescent or a crescent with slightly flattened ends.
Blend the halftones. You need to transition the region between the big white areas and the stark black core shadow. Try smudging the image. If it wears down too light, it can be built up again. There is a little reflected light under the core shadow where light bounces up off the surface, even within the cast shadow. Halftone is the shaded area between the very dark core shadow on the sphere and the light highlight, which you will leave white. Very lightly shade in the cast shadow darkest toward the outline and lightest where it's right next to the sphere. This exaggerates the light reflecting off the sphere into the cast shadow. Doing these light and shadow effects bolder than in real life makes it art. It gives the sphere a lively three-dimensional look.
Finish by darkening the core shadow and blending it gradually into the midtone. Smudge the cast shadow texture smooth, and darken it by rubbing over it with your finger or blender after strengthening the core shadow shading. Clean up around the edges with your kneaded eraser. To soften the highlight, squish it into a rounded shape and press it on the center of the highlight, then lift. Spray your sketched sphere with matte fixative, or it will smear all over the page.
Keep practicing making spheres in a sketchbook, or start doodling with a pencil at work. Doodling an art exercise like this on scratch pads and phone pads is a way to perfect your technique. Apply this kind of shading when it's a soccer ball, an egg or someone's head.
Shading with tortillons (one-ended cardboard blender) or stumps (two-ended blender) is a way to get softer grays in charcoal. Use the point to rub into a very dark area, then draw with the blender rather than the charcoal stick.
You can also shade a sphere with crosshatching, stippling or curving hatching lines that are darkest in the core shadow.
Wash your hands often while charcoal drawing. It's messy, and finger smudges can give you unintended darks.