Pastel manufacturers generally create lighter tints adding kaolin (china clay) or chalk to the pigment mix; darker shades are created by adding 'black' pigments such as PBk6 (carbon black). You can get a light and dark tone to complement each of the 10 you have selected for your mid-tone set, but some aren't absolutely necessary.
Don't bother with dark versions of the cool yellow and orange (dark yellows tend to be a dark green-black) and the mid-tone orange is probably as intense as you will need for now. For the dark tone, take the darkest pastel from the same group as the mid-tone. For the light, take the lightest, or second lightest from the group.
This is what I recommend:
- Warm red: dark and light
- Cold red: dark and light
- Orange: light only
- Cold yellow: light only
- Warm green: dark and light
- Cold green: dark and light
- Cold blue: dark and light
- Warm blue: dark and light
- Cold violet: dark and light
- Warm violet: dark and light
You should now have 28 pastel sticks. Next, you need to get some earth colors.
