The paint finish on this model as supplied is very good, but satin. The idea with the weathering to be done is to present a well looked after locomotive, so the satin finish needs to be altered to a shiny one, but not uniformly so. The cab sides and bunker have been polished with a gentle application of isopropyl alcohol (IPA) on a Tamiya cotton swab. These swabs are very tightly bound and shaped, the ones that I normally use being pointed at the tip. This shape allows me to be quite precise with the area to be covered, and by using the tip rather than the side I can deliberately create an unevenly shiny surface.
This photograph shows the effect when using the tip:
This photograph shows the effect when using the side: