I wouldn't worry too much about filling in the details - if the paint is thin enough to run and pool like that, most of what you've applied is water that will evaporate away. If you want to fix it, though, then yes - simply dry your brush and soak up the excess.
Still, you still generally don't want it to happen. Thinning seems to be the big sticking point for new painters, but brush load is a closely related and (comparatively) rarely mentioned topic. Think of them as being inversely proportional - the thinner the paint, the more it flows, the less you need on your brush to cover a given area. If you find your paint pooling, try loading your brush more lightly (gently touch the tip to a paper towel to draw away the excess, if you still seem to be soaking up too much paint).
If you manage to get even coats but barely seem to be applying any color, you've loaded your brush properly and your paint is simply too thin. Three or four coats for full coverage isn't uncommon. Depending on the color being applied, the color it's being applied over, the exact level of dilution, etc. a solid coat can take anywhere from one or two layers (e.g. lightly thinned "foundation" or "heavy" paints, especially over light colors) to a dozen (e.g. heavily thinned weak colors, like white or yellow, over black).
|