By definition a sponge is any material which is able to absorb and hold moisture. We have established that any fibrous material, a paint brush, watercolor paper,  cloth or paper towels,  or “physical” household sponges can all be viewed as just sponges.

A sponge can be described by its current state of moisture retention. It can be bone dry or it can be totally saturated or it can be in-between in a state from moderately wet to almost damp dry. For our purposes we will use four simple names for sponge moisture states ; bone dry, damp dry, half wet/half dry, and saturated. Bone dry means totally dry with no presence of moisture content in the sponge. For all intent and purposes, a bone dry sponge will not freely wick up external moisture, it must be forced to begin absorbing moisture. To get a sponge to begin to freely wick up external moisture it must already contain some amount of moisture itself. As previously stated a saturated sponge is holding as much water or moisture as it can possibly absorb; it’s thoroughly soaked and no longer will absorb any more water. If we squeeze as much moisture out of a sponge as we possibly can, the sponge won’t be actually bone dry but will still contain a slight amount of moisture and we call this state as being damp dry. A damp dry sponge is “thirsty” for moisture until it again reaches saturation. Between being totally saturated and being damp dry, a sponge is in some state of being partially wet and partially dry for simplicity we will call this half wet/ half dry. 

A sponge will wick moisture based on its current percentage of saturation. At 100% saturated or greater, a sponge will not continue to absorb or draw off additional moisture. Moisture flows from greater moisture saturation to lesser moisture saturation between sponges. Because watercolor paint is pigment suspended in a moist solution, the flow or movement of pigment is from greater to lessor moisture saturation. Again, an important distinction is that 0% saturation, bone dry, will not actively draw/ attract moisture. There is a minimum threshold of moisture saturation, dampness, needed to start moisture wicking action. This is why moist pigment will not flow outside of an area of dampness on watercolor paper. The place where damp paper meets bone dry paper creates a hard edge boundary.

The key to control in watercolor painting is to regulate the differences in moisture saturation between your sponges, particularly between the brush and the paper, but also between areas of the paper itself. ( You can think of a piece of watercolor paper as an almost infinite number of adjacent sponges. )

The easiest place to regulate  the percentage saturation, the amount of moisture, is on the paint brush. As stated, a paint brush is a sponge. If it is totally dry, bone dry, it is essentially unusable for painting with watercolor paint. Remember a bone dry sponge will not freely wick up external moisture so a bone dry brush won’t actually absorb any pigment suspended in water. A paint bush must be first dipped into water to get it initially wet. This dipping in water results with the brush becoming 100 % saturated. A 100% saturated paint brush can’t hold any more water and is best described as ” uncontrollably wet “. Touching the brush against a damp household sponge or a blotter of some type ( a roll of toilet paper or a hand towel ) will cause some of that saturated water to be wicked out of the brush. The longer the brush is in contact with the household sponge or blotter the more moisture is pulled out of the brush. So a quick touch gives you a half wet/half dry brush, usually called a ” controllably wet ” brush. With more additional touches against the blotter or if the brush is held against the blotter for a much longer time, it will approach becoming a damp dry brush. A key technique with respect to controlling the amount of water in the paint brush is to use some type of blotter to wick off the unwanted extra water. A drawback to this technique, is that if the brush is loaded with pigment and water some of the loaded pigment is also deposited on the blotter.  A second important technique for removing some of the water from a brush is to squeeze the bristles of the brush between your thumb and one of your fingers.  Specifically grabbing and squeezing the belly part of the brush close to the heel next to the ferrule. If the brush is loaded with water and pigment most of the pigment will be collected close to the toe/tip of the bristles so squeezing near the heel forces out a significant amount of the water leaving most of the loaded pigment. 

More to come in Part 2 ….