A pin wash is used to bring out details and features of a model through the use of enamel thinners an oil paints.
Oil Paint (colour as appropriate)
Fine detail brush.
Get a small amount of thinners and oil paint of the right colour before starting the process.
Using the broader brush, dampen the area you are working on with the enamel thinners.
Using the fine brush apply as small amount of oil paint to the area you are working on. Adding it near to raised or recessed details will allow the oil to flow round edges to detail and highlight.
If you end up with oil in the wrong place. Simply dampen with a little more thinners and brush and smooth it out so it disperses or moved to where you want it.
Do not worry about getting it wrong, its very easy to clean up with thinners and correcting any errors.
Once you have the effect to dry. Simply leave to dry thoroughly. Enjoy