Updated: Aug 20, 2018
To understand watercolor painting it helps to look at the sponge. Consider how water moves and absorbs into the sponge when the edge of the sponge is touching a pool of water. The water moves from the most wet area and is absorbed into the area that is dryer. If a sponge or a towel is touching the pool of water it wants to move into the dryer area so much that it defies gravity, it will move upwards into the towel.
How does this apply to watercolor?
We have three sponges; the brush, the paper and the paper towel. The water will move from wet to dry, for example, if the brush is dryer than the paper it will pull water into it and will dry the paper or if the brush is more wet than the paper, it will push water onto the paper.
Let's consider how this effects color. If we have a wash of color on the paper and it is a medium/dry wetness and then we put a very wet brush onto the damp wash, the water will push from the wet (brush) to the dryer wash and it will push color away as the water moves onto the paper. That’s called a back wash. The picture above is an example of this.
This principle shows how important it is to when connecting one sponge to the other to be aware of how wet each one is. It's usually best if each area of water matches the other when connecting.
The picture below is an example of a backwash where the wash of color is not very wet and then another wash that IS very wet gets connected to the dryer wash and the dryer wash pulls the water into it which causes the color to move. The dryer wash with color is acting like a damp/dry sponge pulling water into it from the wet pool.
The two pictures below demontrate this principle in the opposite way. This time the color wash has more water and connecting to it is a dryer wash of water, once connected the dryer wash will pull water from the most wet side and when the water moves the color also moves with it. If you wish for the color to remain stationary and not carried away then it is essential to... MATCH WETNESS!
One Way to see the wetness of your brush is to move it around on the palette. And it is ESSENTIAL for me to have a lamp positioned where I can see the relfection of water on my paper easily, the reflection will tell me how wet the paper is. I look at the reflection constantly to gage the wetness.
It is a delicate balance learning to match the wetness of the brush to the paper but over time working with it you will get to know it well. Eventually with time it can become more natural and not take too much thought. Remember “repetition is the mother of skill.” I encourage you to practice at home, whether you are confident with it or not. Don’t get discouraged if you are not pleased with what you are working on, you have to press through It and keep producing and the transformation will happen. When you have a hard edge on your wash that you wish to soften, while it's still wet, lay a wash of water down next to the color wash. Before connecting water to color, be sure that you match the wetness of the water to the color, then it is good to connect by pushing water towards color. It is also good to make sure that your water area is wide enough that the color doesn’t run and make a new edge. The picture below shows an edge being softened. The two sections of water have been matched in wetness.