The less saturated with color your watercolor painting is, the more it can breathe! This is why it is important to leave white spaces, that is, to set aside areas where the white of the paper shows.
Drawing gum is extremely practical, perfect for preserving details and narrow lines.
Apply drawing gum with a fine paint brush to the areas you want to preserve. Allow to dry, then paint your subject without worrying about the covered areas. When the paint is dry, erase the thin film of drawing gum so the white of the paper shows.
Note: Drawing gum is harmful to paintbrushes! Before applying it, coat your paintbrush bristles with liquid soap to protect them.
Wax, while less precise than drawing gum, allows you to create original texture effects.
Draw a horizon line with a stick of wax. Then paint your landscape. Since wax rejects liquids naturally, paint is repelled, leaving a white edge.
Gum arabic is an additive that modifies the behavior of pigments: it allows you to add transparency to washes.
Add a few drops of gum arabic to a wash in a color of your choosing and cover the paper with it. Load a second paintbrush with pure water and dot the paper. Wait a few seconds then blot with a blotter. The white of the paper will show through the dots.
Excess gum arabic can make the coat of paint brittle