You would think that rules in art should not exist because artists need to be expressive, free and loose but that is not the reality. While an artist has free will to express themselves as they wish through their painting, there are endless rules involved. While some of the rules may be helpful, some may restrict you from reaching your potential.
Here are some strict painting rules and when you should break them
Painting from light to dark
When painting solid blacks, you want them to look very relatively dark which means you should not add any white to it. this is because white will make the dark colors look chalky and cloudy. Keeping out the white also gives you a fresher look. Keep in mind that lightening a color is much easier than darkening one.
This rule, however, does not have to apply always. For some landscape images, and pictures that need shadows, you can paint using dark colors slightly over the light colors.
Never use black
It is a common rule among many artists. Most believe that they should not use pre-mixed black paint generally when painting. Black pigments have a way of making the paintings look boring and flat. If you do not need to, you should not mix colors with dark ones. If you mix your dark colors made from combinations of other colors, you will end up with a more vibrant painting.
You can real this rule by mixing colors with chromatic black. This is a more transparent black that allows you to mix them without making them dull.
Cool shadows, warm lights and vice versa
This is a hard and fast rule that every artist can always count on. The light source should be warm and the shadows are always cool.
However, you do not always have to paint the shadows cool and light source warm. When there are reflections, the light bounces off one surface to another affecting the shadows due to color change. This means that an object can have a warm light source as well as a warm shadow and vice versa. Painting with highly reflective colors
Use cool colors to make objects recede into the distance
This rule is basically as is. It suggests that only cool colors work best for receding objects in paintings. This rule does not always work because of different light perceptions during different times of the day. for instance, in the evening, shadows formed by objects and objects at a distance are usually the warmest.
Close objects should be thick and distant objects should be thin
While this rule is a basic for art beginners, the width of an objects is really up to the artist. both thin and thick can work at any distance. For instance, when you are painting a forest, or trees from a distance, there will be patches of cloud and sky that appear between them. You are free to use thick or thin colors for the sky as long as you use the right color temperature and value.
As an artist, you are free to implement your own rules and techniques when creating your art pieces as long as they turn out great.