There are a variety of means, ranging from simple to complicated. but in this instance I used the very basic technique of fine black powder brushed into the lines between panels, around areas people would walk on the real thing, around the edges of removable panels, and around exhausts and vents etc. The effect is to highlight and simulate areas of wear and tear, and make the model look like a miniature replica of a real life object, rather than a few painted pieces of plastic. Well applied weathering like this can make or break a model. Weathering is a tricky process to learn though and not all modellers do it. To little is always better than too much in this case. Some models get finished in states that make them look virtually unflyable. You wouldn't apply heavy weathering to a model of Air Force One. Something like a US Navy carrier based jet you can go to town on, since they spend most of their working lives outside in corrosive humid and salty air, get paint repatched at random, and are used pretty hard. Aircraft at war often wind up very dirty as well, since the maintainers often have better things to do than worry about the paintwork. Certain paint schemes require heavy weathering, since the real life subject was never clean when it wore that paint or markings. I saw a model of a jet used during the first gulf war at the show last weekend. It was very nicely finished and painted, but looked completely wrong since it was nice and immaculately clean. The real thing it was depicting was absolutely filthy with sun faded and peeling paint and grime and stains everywhere.
When applied to a matt surface the powder adheres itself quite nicely. To keep it intact and not leave fingerprints whenever you touch the model usually another clear matt or satin coat is applied. This both seals the powder on and evens out any variations in tone between different paints, decals and the powder, giving a nice uniform tone to the finish, which in itself is more realistic.
Like I said earlier, you weather a model to make it more realistic. Very few aircraft stay pristine for long after being painted. Fluid leaks, exhaust and propellant stains, sun, and general use all combined to degrade the finish.
Here is a French CN235 light transport aircraft I found at an airshow earlier this year. In addition to utility work, it is also used for maritime patrol and based in New Caledonia. So in addition to tropical sun the finish is also exposed to lots of humid salty air, and winds up looking like this:
For reference, the paint surrouding the roundel and code on the fuselage (52 O ID) is the original colouring for the whole aircraft. The roundel marking itself is showing signs of wear; the yellow ring should go all the way around. The weathering for my Skyhawks was a little more subtle. Here is a period shot of one of the aircraft I modelled. Little points to note are the stains around the fuselage and tailplane, some of the panel seams being visible on the lighter areas, and the gunsmoke residue around the cannon muzzle just ahead of the wing.
And here is the model from about the same angle for comparison, with the powder application hopefully gently highlighting the same areas:And that should be the last post about modelling for a bit.
Normal service shall resume shortly.