There is another way that a tone or value can be distributed across a surface, gradation. The weight from a tone doesn't need to be congealed into one shape.
It can be spread as a gradation. Here are some examples of that. The first three are from the Japanese artist Hiroshige. The one above is a particularly good example, but all three are using this device.
Etchers find it a natural device too. In the late 19th century and early 20th century there was a fad for etching that produced a lot of great work. It is under appreciated today because we want color on our walls. But those guys were fabulous designers.The piece below is by James McNeil Whistler. The gradation pulls the eye towards its darker end. The eye tends to follow a tone in the way it is gradated.
Below is an Axel Haig, one of my favorite 19th century etchers. All of that heavy murk at the bottom makes the design.
Below is a piece of Rookwood pottery c.1907 from the Cincinnati Art Museum. The decorative arts are full of great design and the Rookwood art potteries produced lots of examples of designs using gradation. Here is one.
Here is a Sanford Gifford painting from the artrenewal.org site (the online museum, check it out) Gifford has used gradation above in the sky to balance the painting vertically. The tonal gradation pulls the eye upward at just the right amount calculated to balance the horizontality and complexity of the middle of the painting.