I use filters on every model I build. I use odorless mineral spirits / linseed oil at about 10/1 mix. Turpentine, at least the stuff I had, leaves a gummy residue, as does Linseed oil if you use too much. Be sure and seal the model with a clear-coat like Future or similar products. Wet the model with the thinner mix, either by spraying or brushing. Add small dabs of oil paint of whichever color / s you are using and blend with a soft brush. This can be used as an overall effect, or as I like to do, a combination of streaks and spots. This must be done very subtly or it can look hideously wrong. Wait several days for the linseed oil to dry before topcoating with whatever product you normally use.