The concept of contrast in pastel art is often followed by a lengthy discussion of "values", and the rather simplistic admonition to "push your darks and lights" as if that is the be-all, end-all of contrast. But let's consider the meaning of the word "contrast."
In school, we were often asked to "compare and contrast" two or more items in an essay form; this is called a "persuasive essay". For just a minute, think of your painting as a persuasive argument: Tell me, show me, how this pear and that pear are alike, and how they are different. Well, that's easy- they are both pear-shaped, and this pear is red, and that pear is a greenish-yellow. Okay, you're right, but let's go deeper.
How else are they the same? They have nearly the same shape, rather like an hourglass, but not quite. They are both "standing". They are both lit from the right. They both have stems. They are both sitting on a brown wooden surface, with a pinkish-purplish background. They both have reflections of themselves in the wooden surface.
Okay, so now let's contrast them. They are not the same shape- one is squat and "crooked" while the other is long and graceful. While both are upright, one is clearly leaning towards the other. The lighting from the right causes the red pear to be lighter all over than the green one. Each pear's stem is crooked in a different direction. While the chroma of the red pear's reflection in the brown wooden surface is higher, the reflection of the green pear is stronger. The red pear is very hard-edged against the background, while the green pear's edges appear somewhat softer.
Did you notice the notion of "values" was only raised once? Hmmmm....
Look at all the contrast, then, and only one of the contrasting points made was about values! Instead, this painting's contrast depends upon form, colour, and edges. The lean of the red pear, with it's long, graceful shape, towards the green, which is squat and bent, gives us a very interesting contrast to begin with- the composition is already starting out solidly with just that footing of same/different. Because of the same/different shapes of the main forms, they appear to be depending upon each other, leaning on one and other, entwined. The crossed stems further reinforce this notion. Compare and contrast.
On to colour. The red pear is very high chroma'd- that should serve to *pop* it right up forward smacking the viewer in the eyes. But the green pear holds its' own somehow- it is just as strong and bold and stands just as solidly alongside the red- how can that be? Firstly, the contouring- the highlights and shadows- of the red pear is done in analogous colours- colours which sing together in absolute harmony: Red, with purple shadows, and orange highlights- remember that colourwheel exercise? See how it's working here? The green pear, on the otherhand, is an amalgamen of analogous AND complementary colours- and it is the use of the complements which is allowing the green pear to stand as strongly as the red. The "green", itself, leans to olive, which is "made with" orange- which is analogous to red- which is green's complement.... And, it may be difficult to see here, but the "brown wooden surface' around the green pear is deliberately made a touch more red- causing that green pear to *pop* and demand equal attention. The background is assisting in this, with the "peachy" tint behind the red pear holding it back some, and just enough present around the green pear to cause it to come forward.
With all this contrast in colour, you'd think there'd be way too much competition though- why is that not so? Here we can talk a bit of values: If you squint at this, you'll see that the difference in values between the red pear and the background is actually quite small, while, for the green pear, the value change between it and the background is much greater. Otherwise, though, the value range throughout is rather small- the darkest dark is a mere strip on the green pear, and the lightest lights just the highlights- so again, we have variety and unity going on keeping the two disparately chroma'd and formed shapes together.
Edges- see the red pear's sharp, well-defined edges? If they were allowed to go soft against that "peachy" background, the form would've lost impact, would've lost "unity" with the green pear; the two pears so clearly balance each other, the hard edges are necessary to ensure the red pear is leaning into the green. But on the green pear, its' left edge is allowed to soften some, and melt a bit into the background- why? Because there must be something there to stop the eye from wandering off in vain looking for more "stuff" and feeling unsatisfied when there's nothing more. That softened edge causes the viewer's eye to automatically stop for a micro-second to puzzle out the edge, and then it slides right back across to make sure it was right- and voila`! It's back in the painting.
Take a good long look at this piece and "compare and contrast" the various forms, colours and edges, along with the values. (Hint: Look very carefully at the background- very, very carefully. See if you can spot the *colour* shifts). While contrasting values will certainly give you good form, they are not the only way to bring variety- contrast- into a piece, and it is variety within unity which is most interesting to the human eye.
Your assignment, if you choose to learn more for yourself, is to find two or more (not too many now) items which are the same, and compare and contrast them. Show us how they are the same, and how they are different. You may wish to use a few coffee cups, or a pair of trees, or your feet, or even something as subtle as the view all the way across a bedspread- comparing and contrasting the front to the back, the lit to the shadowed.
Give it a shot. Once you understand that's what a painting is- an essay without words- you'll start to see just how to describe what it is you see in pastels.