To speak of a structure of tones is to understand that a painting must have a reading, a harmonious order, just as there must be a harmony of colors in the same way the tonal values must respond to an order.
First of all, our reading is from left to right, just as we read a text, in the same way we begin to observe a painting, only that our reading does not end on the right side as in a text, but our vision will involve the Elements following certain patterns that leave us the objects that are in our painting, then having this in mind we must order our elements in such a way that they allow a smooth and harmonious reading, this order will be given with the elements and the tonal values, this means That the light will guide our sight through the objects and colors of our works of art, the light will form a path, a route that will envelop the whole work resulting in a harmonious and well structured painting in tones.
Trying to explain something that in itself is difficult if not seen, here is an example: let’s say that we have four objects that form a still life which we will paint, let’s say that one of the objects receives a very contrasting light and separated by a Wall the other three subjects receive a very soft light, here is a cut in the scene, a cut in the path of light, an interruption in the reading of the work that cuts the harmony, this is clear that is allowed, But in the pursuit of harmony, rhythm, balance, movement, etc., we must maintain a visual unity that allows us to contemplate a painting without cuts on our visual reading.
Here some images of masterpieces that meet the theme, in these masterpieces we see in a magisterial way how light travels through the scenes, guides us and introduces us to all the main characters, we can not deny how our view enters the works from the Left side and goes around wrapping the characters, a real beauty for our senses.
Note aside it is worth mentioning that in contemporary art these are not a subject to be taken into account, but for those who love the beauty that gives us the classic painting we still have too much to see.