There are a number of matt varnishes on the market for figure painters and modelers. After using the Vallejo Matt Varnish ref. 70520 and Testors Dull Cote spray for years I decided to give the newer Ultra Matte Varnish from Ak Interactive a try...
Gloss Reduction - This is the primary reason to look for a decent matt varnish and this, in my opinion, is where UMV excels. I painted 3 squares in red and then 3 more in black. The first square is the acrylic paint before any matt varnish is used. The second is where I have applied Vallejo Matt Varnish. As you can see there is a considerable sheen reduction but the final squares show where I have used UMV. The finish dries dead flat and the color appears richer. There is simply no comparison. UVM is the real deal...absolutely dead flat and the color really pops!
Consistency - Some acrylic varnishes are quite glue like, but UMV has a milk like consistency. The advantage to the thinner consistency is, of course, that it runs through your airbrush nicely. You can load it straight into your airbrush and during testing I had no problems running it through an Iwata Eclipse on a low pressure. The results were as good as my favorite aerosol Dull Cote with the advantage of having much more control.
As a matt medium UVM has a nice adhesive quality and can be used as carrier or pigment fixer- mix a little UMV with a pigment and easily make satisfying nature effects.