I just finished a nice colour modulation job on the upper surface of an aircraft.
I sealed it Vallejo Acrylic Gloss to protect the job and provide a surface for the decals. Unfortunately, the gloss has made the paint job go so dark as to make the modulation largely disappear!
It doesn’t matter what brand. Any glosscoat will alter the reflectivity of a flat basecoat and make it appear darker. Some colours will be affected more than others.
The only way to knw what the effect will be is to test the same paint/process on a paint mule before applying it to a live build.
Nah, It’s not a matter of Vallejo, as has been mentioned. Most clear glosses intesify or deepen the color as well as in the case of metallics for instance increase the highlights, magnify the refectance. The glossier it is the more so the effect, generally speaking.
Flat finishes are flat because they are rough. The roughness scatters the light and makes the color look lighter than it would be otherwise. When you apply a clear coat, you fill in the “valleys” between the “hills” of the roughness, smoothing it and reducing the scattering. An additional flat coat will restore some of that roughness but not completely.
I suggest avoid clear gloss altogether. If you are trying to avoid “slivering” when applying decals, just polish your flat paint until it is smooth. This will darken the color slightly, but not nearly so much as applying a gloss coat. Apply decals using Micro Set and Micro Sol, and when they are dry, spray your final clear coat.
I put the flat clear coat on and the colour is lighter, but a lot of modulatipn detail has been lost. In future I will have to exaggerate the modulation, so that when all the clear coats are on, it will look about right.
The model in question is detailed inhttp://cs.finescale.com/fsm/modeling_subjects/f/2/t/189625.aspx