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or a mix of all those sprayed in a zenithal lighting fashion.
Woah, that sounds hardcore. Does it make much of a difference? As a long-lapsed aeromodeller, Tayima grey spray primer was the only one I've heard of people using. Though I suppose the advanced will pre-shade panel lines and the like.
Thrustvector-
I really like it for painting with Inks (or contrast paint)
I prime my miniatures black and then white in a 30° cone at the top. Straight from the spray can.
That leaves the miniatures white on top, black on bottom, with a kind of rough gradient between the two. Now if you add the translucent colours, the roughness will be gone and instead you have easy shading in parts where light usually doesn't get to.It's quite handy once you get the hang of it, but really only works when painting with transparent colours. On normal opaque colours the effect is minimal.
Murphy's_Law
I would ask the person who painted it for you what they used, and then use another coat of that on it. Safest way really.
I would advise against a spray varnish, as you can easily mess up a nice paintjob with it.
I can recommend Vallejo Varnish. Matt, Satin, or Gloss, depending on what you need.
@JT People very much still use white. Or Black, or Grey, or a mix of all those sprayed in a zenithal lighting fashion.