When you become comfortable working with 5 values from dark to light, it's time to push that envelope to 10 values!
Remember if you have 2 values, just light and dark, you still get an idea of form.
If you have 3 values you have dark, medium, and light which gives you 3D.
If you have 5 or more values you create the illusion of realism which is what most representational artists aspire to.
10 values requires some training. No one is born seeing and recognizing all these subtle nuances of shading and color-you have to consciously train yourself. It's like meditation, the simplest thing ever, but it requires us to wade through our complicated world to see it.
The best way to see it is to describe it with your pencil or charcoal first. Here's two value scales, one in pastel, one in graphite. When you do something with your hand, you create muscle memory which allows you to do it again, and to see it more clearly.
We are artists, and therefore visual learners, so it's important to actually do it to see it.
Start at the two ends of the value scale by sketching in the darkest dark and leaving white paper for the lightest light.
Note: it really doesn't matter if your consider #1 to be darkest dark and work your way to 10 as lightest light or the other way around. Number the values how you see fit. Since we work from dark to light, I always work backwards using 10 as darkest dark and 1 as lightest light.
Now split the middle and make 6 the halfway point-fill it in half as dark as your darkest dark 10. Split it again by making 3 which is half as dark as 6. Now its easier to visualize the values in between. Shade very lightly the 2 which is the lightest you can get and still be adding graphite to the paper. Now you have values 1, 2, 3. Its easy to go one shade darker than 3 to get 4. Then you have the 6 already in place, and the 4 already in place. The 5 is between them, making it easier to see.
Now we move to the dark side of the scale and split the difference between 6 and 10 by shading in 8 between the two. You can gauge the 7 and the 9 by looking at the neighboring squares and shading accordingly. This gives you a value scale of 10 values from dark to light.
Cut this scale out and hold it up to your subject. This helps you see where the color you are looking at fits the value scale. You make have to squint your eyes to see it as a value. Judging the value of color is a skill that you can only build through training your eyes and making mistakes. No one is born with it! We all struggle through developing this skill.
There are many products on the market designed to help you see values, but nothing beats sketching with your hand so that your eyes and hands have the "feel" for it. If you really don't see it, try putting on a pair of red sunglasses. I buy these in bulk for my plein air class to help people learn values outdoors. In bright sunlight its harder to see values. Red neutralizes all the color in the landscape into shades of red which your mind can more easily interpret as greyscale or values.
Values are most often the problem with beginner painters. Beginners are afraid to go too dark and stay in the middle of the value scale making everything look flat and losing the form of what they are painting. Being able to differentiate 10 values is a worthwhile skill to build if your goal is to paint from direct observation; this means in plein air, still life or portraits from life.
When you work from a photo reference, the camera eye flattens out many of the values so all you really get is about 5-6 values in a photo. You can still create a beautiful interpretation using a handful of values, but nothing beats the clarity of working from life. The more you look at a subject in front of you, the more you "see" in terms of subtle shading and nuances of color and light.
