I think all watercolor artist have a love-hate relationship with masking fluid or frisket, as some call it. We love it because it is similar to rubber cement and can be painted on to cover any shape or area that you want to stay white. It protects the white of the paper when you paint over it with watercolor while doing a large wash of color.
We hate it because when it is removed we are left with very hard edges and often realize that we didn't do the best job of painting the masking fluid in a smooth manner. Sometimes, we have to spend time trying to soften the hard edges and blend them in to the surrounding paint.
For Full of Light I used a liner brush and painted quick, smooth lines to create flowers, leaves and the vase. When I applied the bright colors I was free to paint quickly and freely!