Jackson's Picture Varnishes are an almost colourless liquid which dries quickly to a clear non-yellowing non-blooming film. This product is made of acrylic resin, stand linseed oil, mineral spirit. Use white spirit for cleaning brushes.

This Picture Varnish is a solvent based product and is ideal for use on oil based mediums, not water based. When using acrylics or water colour paints you should use a spray varnish so as to not disturb the paint underneath with abrasive brush stokes.
Other points to consider are; the drying time of the paint. The paint must be thoroughly dry before applying any varnish otherwise water and air particles become trapped between the painting and the varnish and create a whitish sheen. It is also very important to mix the varnish extremely well by shaking the tin thoroughly and leaving it to stand for several minutes so that all the bubbles settle resulting in an opaque fluid ready to apply.