Ansel Adams and Fred Archer came up with a technique of developing photos to their fullest
light/ dark potential called the Zone System. Every aspect of detail is captured and not lost in over-dark values nor “blown out” with too much white.
In the Zone System for photography, there are eleven steps in the scale, starting from black and
working up to white. Note how each step “flutes” or appears lighter at the bottom and darker
at the top.
I have found that 11 ‘zones’ are very good for photography, especially when photo processes are involved. However, If we were to render out each zone with pen, pencil, paint etc, we would find that “black” and “near black" are almost the same. In fact your monitor may not even display the difference of these two. Check your brightness levels if that is the case. To avoid these two values dropping into each other (without thinking in terms of gradients), I have narrowed the scale so that ten zones can be used. These are derived from computer values with regard to gray fields.
Each zone is 10 percent lighter or darker than the first. Thus, white is zero or the color of your paper (as an additive value) and Black is 100%. Conversely, black is 0% as a subtractive (as in light value in Photoshop) and white is 100% or pure light from the screen. This is not exact and
you can see that the “fluting” is more subtle as a result, but I do find that it works in terms of seeing the steps or values.
This means that you must decide what is to be the darkest portion of your drawing whether you build up your values from white to black or not. The next and most logical step would be to know where your lightest portions are. If your darkest portions are laid in at only a middle value (50%) then you can only get lighter. The resulting image will end up looking washed out or low contrast because not all of the zones have been addressed.I have gone even further (though this information is by no means my own) and included a even further condensed scale that allows for five values, again based on computer scale. Here are five values, 5 as pure white descending down to 1 being Black. Note how little "fluting" is happening here but this scale leaves no doubt what values are available. My suggestion to students is to get used to using these five values in every work, ultimately leading you to be confident enough to work in the original value scale seen in the Zone System.