The above gallery is a gallery of Birch Trees on Yupo paper. You can see each image larger by clicking on it. Some of the whites are by pulling out the color, some by adding a resist such as a tape or a contact paper, and others by painting over with an opaque white such as a Posca pen, acrylic paint, or White Gell pen by Uniball.
The above gallery is an example of Birch Trees painted on tiles and sealed. You can click on each image to see larger.
Notice how the backgrounds are lighter or darker than the trees to form a contrast.