The intention of shading is to
give your drawing scene three-dimensionality. When you are
finished with shading, your drawing should look like it is
situated in space with rounded edges and parallel lines that
seem to converge at infinity.
The value of an object is a
measure of its darkness and lightness. Values vary from
completely white to completely dark on a continuous scale. To
start your value training you can divide the continuous scale
into five intervals to which you assign the average value within
each interval.
This idea is summarized in the
construction of a so-called 5-value scale:
Step 1. Draw 5 connected
squares. Make the first square from the left completely black
and the fifth completely white.
Step 2. Then, block-in the
middle square with a value midway the two end values. This one
is called the "halftone" (or medium gray).
Step 3. Next, the second box
from the left is filled in with the average of medium gray and
black. This is the "dark gray" value.
Step 4. Finally, block-in the
fourth box from the left with the average of medium gray and
white. This is the "light gray" value.
With these 5 values you can
achieve very realistic shading and for most purposes may
actually be quite sufficient. The idea is to practice these 5
values a lot so they become second nature.
Now, armed with this 5-value
scale we can now begin the shading process (i.e., the
application of the 5 different values to your line drawing).
Always be aware of the location
of the light source(s). To practice your 5-value scale it may be
a good idea to first investigate the value distribution of scene
that is lighted with just one light source. This way you will
get the feel of how light distributes itself among sets of
objects.
After a while you will become
aware of certain value patterns that are consistent with the
location of the light source. Of course, theoretically, all you
need to really do is correctly observe all the values and then
correctly reproduce them on your drawing paper. Still, if you
internalize the flow of light as it relates to a light source,
the task of judging values will become much easier.
The procedure starts with
assigning to each of your line drawing areas one of the values
of your internalized 5-value scale. You do that through careful
observation. Later, during the next phase, we will blend the
boundaries between the multiple areas. These blended areas will
be called transition areas and they will have the average value
of the two neighboring forms.
It is also helpful to think of
the values of the 5-value scale in terms of the 5 so-called
elements of shading:
a. Full Light or Highlight - An
area where the light hits the object straight on is said to be
in full light. It is the white represented by the first square
on the right of your 5-value scale, i.e., the white of your
paper.
b. Cast Shadow - A cast shadow
has the value shown in the box farthest the left on your value
scale. This value occurs in places that are completely blocked
from the light source and any reflections. These areas are
usually to be found among the shadows the object casts on other
surfaces.
c. The Halftone - This is the
medium gray value of your 5-value scale. The halftone is the
value of an object that in bathed in average daylight, i.e.,
light that is right in between dark and light.
e. Reflected Light - Reflected
light corresponds in value to that of the fourth box from the
left on your 5-value scale. It is often seen as a narrow streak
of light gray between a shadow edge and a cast shadow. It is
light that reflected from neighboring surfaces onto your
objects.
Note that this type of light is
never totally white. It is important to render such light
carefully because it contributes considerably to the illusion of
three-dimensionality and roundness of the objects.
d. Shadow Edge - The second box
from the left on your 5-value scale represents the value of a
shadow edge. Shadow edges are found in areas between cast
shadows (or reflected light) and halftones.
In closing, an acceptable line
drawing, the 5-value scale, and the 5 elements of shading are
all you need to produce a shaded drawing. The idea is to use
short parallel lines to build up the different values. A sphere
on a surface lighted from one side is ideal to practice the
interaction of the 5 shading elements.
