You put down a blue wash and leave it for a little while. Then you come back and add another stroke. A few minutes later, a light edge of something shows up in the place that the new wetness ran into the previous color. People often call this a bloom or backrun. It looks fine if you wanted it. It’s a nuisance if you were going for a flat wash. One thing to note about blooms is that they’re never accidental. More often than not, there was some extra water on one section of the paper compared to the area next to it.
Watercolor on wet paper acts differently than on damp or nearly dry paper. On very wet paper, the pigment moves around more easily and spreads out in a softer edge. As the paper becomes less wet, the paint sits down into the paper. Then, if you introduce a brush that is wetter than the paper or a puddle of diluted color, you might see a bloom. The extra water that you apply might run into the partially dried area and push the pigment outwards. The result will be lighter in the center and a darker irregular edge.
An exercise that helps is to paint three rectangles with the same color. Let the first one stay wet. Let the second one get soft. Let the third one get nearly dry. Dip a brush in clean water and touch each of the rectangles. See how far the water spreads and how it changes as the paper dries. The wet rectangle will probably blend more freely. The soft rectangle will have a higher chance of blooming. The nearly dry rectangle might make a hard edge. This is an easy way to practice determining paper moisture without needing to worry about it while doing a complex painting.
The amount of water on your brush is just as important as the timing. A wetter brush than the paper can carry too much water and disrupt the pigment that has started to settle into the paper. Check your brush before you touch a soft wash, and if the tip is dripping, remove the excess water. Glazing over dry paint is different. Because the paint layer is dry, you have more control over the process. Just don’t go back over the paint too many times, or you’ll start reactivating the old color.
Blooms can happen when water pools unevenly across the sheet. A puddle of water at the bottom of a wash can migrate backwards as another portion of the wash starts drying. Tilting your paper too much, applying more water to one part of the wash than another, or switching from a large loaded brush to a very wet small brush all can lead to blooms. While painting a flat wash, it’s better to maintain a consistent line of water at the leading edge of the wash rather than trying to correct spots as they occur.
If you get a bloom that you didn’t want, correcting it immediately isn’t always the best approach. Continuously going over the partially dry area can cause more edges, lift pigment, and scratch the surface of the paper. The safest option might be to ignore the wash and let it dry completely, and then determine if the bloom needs correcting. If you need to, you can glaze over the edge later to even it out without risking multiple wet strokes in the process.
Learning to recognize paper moisture turns blooms from mysterious watercolor phenomena into things that have a reason behind them. Look at the sheen on the paper, pay attention to the wetness of your brush versus the surface, and see where puddles of water gather. When you aren’t sure if an area is ready for another stroke, adding water to it is generally the worse idea. A few seconds of checking can save you from having to fix a bloom that was made bigger by trying to correct it.
