Hi all,
Pre-shading is done prior to applying the decals.
Instead of masking and airbrushing the pre-shading, I've used the same technique used for other models of mine.
A white primer was airbrushed over the parts, which is required for applying the clear 'Aviattic' CDL and PC12 decals.
I then lightly polished across the raised detail using 'Flory Models' green sanding sticks.
I also pre-shaded areas such as wing, aileron and elevator trailing edges and added the wing underside internal bracing wires with a pencil.
The wears away the white primer to expose the light grey colour of the styrene.
The only masking needed was for pre-shading the wing front and rear spars and the fuselage formers frames.
I polished between the applied masking strips.
Finally, I airbrushed several coats of 'Alclad' Aqua Gloss 600 clear coat over the parts as a base for the decals.

The polished-out pre-shading detail will show through the 'Aviattic' clear decals, more so for the CDL than the PC12 decals.

Mike