Varnishes in general can thicken if the bottle is not closed properly. The solvent will evaporate slowly. The dissolved resin does not evaporate, with the result that the percentage of resin in the varnish becomes relatively higher and higher. However, by adding a little white spirit (Talens White Spirit 090) and then shaking the mixture well, this problem is quickly solved. It is important not to add too much white spirit. The amount of resin in the varnish will then not be sufficient to offer the desired protection to the work.