Colour using small circles and light pressure. Leave the area nearest the light source uncoloured, blending into it for a seamless graduation of colour. I am aiming for a red area so have selected Dark Chrome yellow 9201-109 to represent the highlighted area.
Blend into the previous layer with lighter pressure building to medium pressure as you move away from the light source, leaving free an area of the previous layer nearest the light source.
Repeat Step 1 using a slightly darker shade. This is where I introduced the red, using Geranium Lake 9201-121 which reflects the truth colour the object. You can see this is starting to build the graduation.
Repeat Step 2 using the slightly darker shade used in Step 3.
If you want you colouring to look vibrant, you can now add another layer using firm pressure, leaving an area of the previous layer, nearest the light source, free. Be careful no to not press too firmly and flatten all the tooth in the paper. If you want a more delicate finish, skip to Step 6.
Add an area of a darker colour at the edge farthest from the light source, using medium building to firm pressure, to create the shaded area. I have used Dark Red 9201-225.
To really accentuate the shadows use your darkest shade, I tend to favour a purple, Mauve 9201-249, as it adapts to whatever colour it’s worked over, and use small circles and directional strokes along the edge of the area furthest away from the light source.
Finish by burnishing to create a smooth finish. This can take some practice as using a firm hand flattens the pigment into the texture of the paper to make it look nice and smooth, but it also can move the pigment around. I burnished using white 9201-101 over the highlight and up to the colouring laid down in step 3, then swapped to the Dark Chrome Yellow 9201-109 feathering back up to step 3 and down to step 6. You can subtly change the colour of you area by burnishing with different colours so it’s worth having some fun experimenting!