Terms you should understand
- Asymmetry A common form of balance. Unlike symmetrical balance, the objects do not reflect one another on either side of the implied vertical axis, yet it has a balanced visual weight.
- Visual Weight is essential to balance. The shapes, forms, colors, etc. (artistic elements) used in the composition make up the elements referred to as visual weight.
- Artistic Elements are the elements (shapes, forms, color, etc.) used in a composition
- Picture Plane The area in which you draw, paint, etc. For example, an artist fills a piece of paper with a drawing; that area is the Picture Plane. In a painting, the entire surface of the stretched canvas is considered the Picture Plane, etc.
- Composition The relationship between the parts or elements of a work of art. For example, the arrangement of balance, rhythm, color, etc., on the picture plane.
- Positive Space is the form of the subject/object(s) in a composition.
- Negative Space is the area that surrounds the positive space and shares the outside edges with the subject/object.
In my experience, if there is a compositional problem with a design, poorly placed visual weight is often the culprit! Understanding how balance and visual weight work is one of design's most critical concepts. I have found that many of you instinctively understand the concept of asymmetrical balance, but once we begin breaking it down, it can feel confusing!
Review of the basics of balance (as seen the in the blog on symmetrical balance) Understanding the concept of visual weight is the key to understanding balance.
Unconsciously, the viewer imagines a vertical axis running through the center of the picture plane. The visual weight of the artistic elements on either side of the vertical axis establishes balance.
We unconsciously view the picture plane as having a top, bottom, left and right side. We, in the U.S. learn to read left to right, so view art from left to right.
We unconsciously view the picture plane as having a top, bottom, left and right side. In the U.S., we learn to read left to right, so we view art from left to right.
The visual weight of the artistic elements on either side of the vertical axis establishes balance. This statement is true for both symmetrical and asymmetrical balance. If you haven't done so, please read the blog on symmetrical balance.
Asymmetry balance often gives a causal feeling to the viewer. But don't be deceived; asymmetrical balance is more complex for the designer to achieve correctly than the other forms of balance. Instead of repeating the same artistic elements from one side of the vertical axis to the other side, as in symmetrical balance, asymmetrical balance uses different artistic elements on either side of the vertical axis to create balance (equal visual weight).
The goal of asymmetrical balance is that the (visual) weight of the artistic elements equals out from one side of the vertical axis to the other side. In the painting Tables for Ladies, below, the blond woman on the left side of the vertical axis (size and detail) balances against the row of food (detail and color). Both sides have their own type of visual weight, and yet each element of visual weight balances one another. To get a clearer understanding, let's look at the five elements of visual weight.
Tables for Ladies, by Edward Hopper, 1930 (The Metropolitan Museum of Art)
Visual weight
Each artistic element used on the picture plane possesses some quality of visual weight. The challenge is getting the visual weight to equal out on both sides of the vertical axis. Below is a breakdown of the five elemnets of visual weight.
Size 
Place two squares on the picture plane, both with the same value, created in the same manner, and equal in every aspect but size. The larger of the two squares has more visual weight because the larger the item, the more space it takes up.
Lincoln, by Robert Rauschenberg, 1958. (The Art Institute of Chicago)
The image of Lincoln on the left side of the vertical axis is an example
of size and visual weight.
Artwork by artist Ursula Brenner.
The darker value on the left side of the vertical axis is an example of value and visual weight.
When you have a single colored item in a grayscale environment, the eye automatically goes to the color first. It's the make-up of the eye.
3- Dimensional vs. 2-Dimensional 
Place two squares on a page, equal in size, value, etc., except one appears 2- dimensional while the other is 3-dimensional. The 3-dimensional square has more visual weight. This type of visual weight seems to be closer to the viewer due to the addition of depth. It creates the illusion of absorbing more space on the picture plane.
In thie example the 3-D baseketball has more visual weight than the 2-D background.
Negative/Positive Space & Asymmetrical BalanceThe negative space is a compositional rule I like to consider with asymmetrical balance. In the piece by Hernri Riviere (below), the composition has a strong negative space that creates visual interest, adding to the all-over visual weight. Before breaking it down, let's take a quick look at negative/positive space.
What is Negative & Positive Space?
Positive space is the subject/object(s) on the picture plane. Negative space is the area surrounding the subject/objects (positive space), sharing outer edges with the subject/objects. In the image below, the yellow vase is considered the positive space, while the black space is the negative space.
Negative & Positive Space and Asymmetrical Balance
Now that you have a basic understanding of Negative/Positive space let's look at how it affects visual weight and balance.
Funeral under Umbrellas, by Henri Riviere, 1895. (Bibliotheque Nationale de France, Cabinet des Estampes)
The two main elements of visual weight on the left side of the vertical axis are color and detail. Let's address the color first. We see warm colors before cool colors. This is especially true with purer colors. The majority of the warm colors in this piece are located in the top left, corner of the picture plane. The red chop is also placed on the bottom left side of the piece.
The major elements of visual weight on the left side of the vertical axis.
The second important element of visual weight on the left is in the top left corner, which is the horse-drawn hearse. This is detail. It is an essential part of the story that the image is communicating. The audience of that day immediately knew what the horse and hearse represented. By adding the bright splashes of color near the horse and hearse, Riviere adds additional importance to that area of the composition.
The major elements of visual weight on the right side of the vertical axis.
On the right side of the vertical axis, the main elements of visual weight are size and value. The figures in the rain are created with mainly dark values. As the figures get closer to the viewer, the size of the figure increase.
Great uses of negative/positive space
The interesting shape that the negative forms create drama in the print. It contributes to the balance, and design.
Credits: Some of the information in this presentation comes from the book, Design Basics, Seventh Edition by David Lauer