I have made it a habit to apply a gloss varnish over my acrylic paintings and drawings, this is done for two reasons, to allow me to clean the surface of dust without damaging the underlying work and to give a boost to the intensity of the colours. I have in the past used spray cans of varnish which are easier to work with but this easiness is outweighed by the extra costs involved. I have found that the Matisse varnish does the job well and at a far lower cost