Most of us became acquainted with the simplest type of stencil printing in kindergarten: a template cut out of paper, such as a heart shape, is placed on a sheet of paper. Watercolour is sprayed onto the paper with a spray grid and a brush. When the template is removed afterwards, everything underneath has remained uncoloured. If the shape is cut out of a sheet of paper on the inside, the colour is then only where the opening was in the masking paper.
This simple stencil principle is also used in the professional printing process of screen printing: Here, the ink is pressed through a stretched screen fabric onto an underlying surface. Where ink is to be pressed through, i.e. at the image areas, the mesh is open. At all other points, the mesh openings between the threads of the fabric are closed so tightly that no more ink can pass through.
And last but not least, stencils can be used to mark large objects, such as wooden transport boxes or walls, with spray paint. The stencils required for this can be cut from foils, self-adhesive films or cardboard by computer.