Sealing a watercolour painting on paper is a way to preserve the colours of the painting for decades and minimise fading from exposure to light. A few layers of a ultra-violent-resistant matt clear-coating properly applied provides protection without altering the appearance of the painting as mounting behind UV-resistant glass might. After spraying, the painting is ready for mounting and framing, with the clear-coat providing protection from light and physical damage.
Place the paper watercolour painting on a flat surface that provides enough space to work. Work in a dust-free area to avoid dust settling on the sealant as it dries.
Shake a can of UV-resistant acrylic clear coat vigorously to mix the material and ensure a smooth, even spray. Hold the clear-coat about six inches from the watercolour's surface, then spray the painting with a light coating, taking care not to let the coating pool. Keep your arm moving constantly back and forth to create an even coat on the page without saturating the page. Allow the layer to dry for 30 minutes.
Apply two additional layers of clear-coat to the watercolour, following the same procedure. Allow each layer (except the last) 30 minutes drying time. Let the final layer dry overnight.
Glue the paper to a canvas for framing using a fluid-matt medium brushed on the back of the watercolour paper and the canvas. Press the two together to form the initial bond, then flip the canvas so the watercolour is face down. Press the rear of the canvas from the centre outward to remove any air bubbles trapped between the canvas and paper. Place a piece of Plexiglass large enough to cover the watercolour on the back of the canvas over where the watercolour is attached, and then place several large books on the Plexiglass to weigh it down, aiding in the bonding process. Leave the weights in place for two hours.
Remove the books and the Plexiglass. Flip the canvas over and wipe away any of the matt medium that squeezed from between the paper and canvas with a piece of cloth. Allow the paper to dry in place overnight.
Use a paintbrush to apply two coats of a gloss-varnish mixture on the canvas and watercolour. The varnish should be mixed with three parts varnish to one part matt medium, with a little water added for smoothness,