SPONGES FOR CREATING TEXTURE
NATURAL SEA SPONGES
Sponges are wonderful for creating texture in watercolor painting - but not all sponges are created equal. As well, they do not all create the same type of texture - each one will do something different for you.
Natural sea sponges come in many sizes and shapes, and are now used as home spa objects. They are rock hard until you put them into water, and then they feel rather like an insipid handshake - soft, wet, limp. Each sponge will have unique capacity as each has different sized holes and surface, creating varying texture on your watercolor paper.
Expandable sponges are hard, and thin like sheets of paper until you immerse them in water, and then they become like a regular sponge and expand to the size you see on the right of the picture above. You can cut these into sizes that you desire either before or after soaking in water.
Cellulose sponges are the only synthetic sponges that I use in my painting. These can be found at your hardware store (probably in the tile and grout section). They are sort of like styrofoam. You cut a strip off the end of the sponge as you see in the above picture (use an Xacto knife - don't try scissors... they don't work on this sponge!). Once you have cut off a strip, you begin to tear that section into smaller pieces. A cellulose sponge will almost always end up tearing into pieces that have one pointy part and a broader part. These are GREAT for painting trees or foliage.
No matter which kind of sponge you use, here are a few tips you should keep in mind. When you wet the sponge, wring out as much water as you are able so that it is almost dry again, then pick up the with the part of the sponge you wish to create texture with. Experiment with how wet to have your pigment, how hard to press onto the paper with the sponge, and what the different edges and surfaces will do for you. I have found that there are some sponges that I use all the time, and others only for special tasks. I usually have a good puddle of very wet paint when I use the cellulose sponge, and I drag it through the pigment until it is really soaked with color. Then I begin to paint with it, using all the surfaces, the tip, the wider sections and so on. (By the way, you can cut off any edges you do not like the shape of.) With the sea sponges, I have pigment which is straight from the tube, or quite creamy, on my palette, and I touch only the edges of the sponge to the paint before taking it to the paper.
Textures and things you can create with sponges: trees, foliage, clouds (lift them out of the color with a sponge that has no color on it), texture on rocks, beaches, roads, and probably a hundred other things!
I never use the foam sponges that you can buy for kitchen use in my watercolor painting. I save those for painting bricks in acrylic for stage sets! Other than that, I have no use for them!