For clear varnishes I use artists acrylic type namely Windsor and Newton Galeria from the Range, far cheaper than any modelling type, I spray it through a 0.2mm or 0.3mm nozzle thinned slightly with water, available in bottles up to 500ml in Gloss, Matt and Satin, sticks to plain plastic fine and over paint finishes. I only bother with the Gloss and Matt and mix my own Satin from the gloss and matt.