There are many 'varnishes' to choose from:
Pledge with Future Shine (clear, acrylic, water-based floor polish, apply full strength, then dull-coat); watered-down PVA (White) Glue; matter clear coat spray paints, available at all hobby stores/Wal-Mart;
Testors Dullcoat (hobby shops that carry Testors paints);
Mod-Podge matte (similar to PVA, but use full strength out of the jar); clear Polyurethane (water- and solvent-based, available at DIY stores like Lowe's, Home Depot, etc. -- will likely need a dull coat afterwards); and many others.
If you are unfamiliar with
The Dip (
Minwax Polyshades Urethane-Stain Tudor/Royal Walnut), and
Magic Wash (
Pledge with Future Shine + acrylic paint), I recommend you
Google these terms. They are shading techniques which may interest you. I use a simple, block-painting technique, followed by either
The Dip, or
Magic Wash, depending upon the figures/piece in question. If I can use black shading, I reach for the
Minwax Tudor (black); if I want the piece/figure to appear dirty, I reach for the
Minwax Royal Walnut (dark brown -- perfect for Army Men figures, gives them that 'in the field for a while' look...); if I need some other color for shading, I mix the appropriate acrylic paint [red, purple, blue, whatever color is needed; used blue for my
Winter Wolves, and my Ice Bridge terrain piece (no picture posed -- yet)] with some
Pledge/Future. They transform a very basic, block painting technique, into something much better, which looks really quite decent, at arm's length. They speed up painting ten-fold, or more. They will not turn your figures into competition winning entries, but they will speed up your painting, dramatically,
if you like the results... Otherwise, ignore, and do what you prefer. Cheers!