Here is my method of applying an Oil Wash.

My first step is to give the model a couple of Klear Coats, after decalling, and leave for at least 24 hours to cure.

NOTE - I say a couple of coats, because I found the turps melts through the Klear and if not thick enough you start can rubbing away the paintjob.

Typical items used:-

Plastic mixing palette

Winsor & Newton Oils and English Distilled Turpentine.

When the Klear coat is ready, I will fill up my mixing palette with turpentine, add a very small amount of Raw Umber, and mix for a minute or so, until the paint is fully diluted.

Next I use either a Humbrol 3/0 brush or a Pro Arte 0 brush (dependant on the size of model), and apply to the panel lines and angles. When I have completed this, the model is set aside for about 4 hours to set up slightly.

Example of my first attempt (but using Burnt Sienna).

When the 4 hours is up, I pour out some more turpentine into the mixing palette, and using a q-tip soak in the turps and gently wipe over the wash in the direction of the airflow. This will loosen the wash on the surfaces, allowing you to wipe away the excess. I also use a kitchen towel to wipe down the excess turps. It is best to do this a small area at a time.

When I am satisified, I will put the model to one side for a day or two to allow the oil wash to harden, then I will seal it with the appropriate final varnish coat.

And heres the finished example from above, after an acrylic Pollyscale Flat coat.

The wheel wells and landing gear were given a Tamiya Smoke wash.