Hi !
I ve bought a varnish mat spray but i ve never used it. All of my ship aren't varnish for the moment. I will probably use the spray on the huge ship like the transport or the tantive i m working on.
For the tie panel it's a layer of grey, nuln oil with water on all the grey, then when it's half-dry, i put some nul oiln in the corner and along the structure to make some shadow and contrast.
Then i put some thin lines of the original grey in the center of the panel to highlight a bit.
And finally a light light dry brush to highlight the relief straight lines.
For the damage on the wings, i take a wire cutter to cut the form and then, with a xacto, i try to "refine".
Some imperial primer with water, and hop ! It's done