This cabinet was made from MDF which if you have ever painted will know has a slight textured finish, (kind of furry) so I thin the paint right down and spray a couple of coats on as this soaks in well then hardens allowing you sand the textured surface of the MDF nice and smooth. I then apply several more normal coats, sanding each one in-between being careful not to go to heavy on the corners as they are easy to sand through back to the MDF. Most people I talk to think the top coat is the most important, but to be honest is the base coats that are more so, as if these have imperfections in them so will the top coat, so it's worth while taking your time over this, and getting the base coat to the standard you want the whole item finished to.
I spray paint just about everything as it gives a much more even finish but you can brush paint, just make sure you have a nice soft bristle brush, and paint which takes several hours to dry, as if it's a quick drying paint you will find if you over paint, it streaks leaving nasty lines.
Now comes the fun part. As I said I have read tutorials on using mustard which is fine on small plastic kit size models but on larger things, two things happen. Mustard dries out over night meaning you have to work very quickly once its applied, and second if you're using proper automotive based spray paint, it reacts with the mustard drying it out and sticking it to the work piece which is not so good, so I use latex. You can buy it at most model shops or on eBay, then it's just a case of with a stick, and I say stick and not brush as we want to dab this on not paint it, stick it in the latex, then give it a shake, then just randomly dab it along the edge. As you can see in some places its big dobs, others just a thing line along the edge and this is because chips are normally either from excessive wear, or knocks, so do a combination of both and see how it looks. The good thing with latex is if you don't like it just rub it off and start again.
When done leave this for several days to dry, or when spraying the edges wrinkle up.
Next you need to respray it all again in this case matt white, as this cabinet is also going to look dirty when done and matt paint dirties up much better than gloss or satin because of its rough texture.
Now to get it looking really lifelike, you need the paint to be thick, as this then gives the chip a proper edge, looking like it's a proper chip not just added for effect. I use high build primer, as this is much thicker than normal white primer, and give it two or three heavy coats. If your hand painting it just go over it with three or four coats of white or whatever colour primer you want, letting each one dry fully between coats.
One of the good things nowadays is most large DIY stores can mix the paint to any colour you want which is useful and as for auto based paint, well they can do the same, but bear in mind high build primer doesn't cover as much as normal primer so always buy twice what you would need if you were using normal primer. For example the two cabinets I made took 3 litres of mixed paint, which is twice the amount of standard primer that would have been needed.
Next you need an airbrush and can be a cheap one run off a can of air, as it doesn't really matter as its only for the base coat, in this case silver. This technique can be used for whatever chipped colour you want, but in this case I was going for a chipped metal look, hence the sliver, but just remember whatever chipped colour you go for, try and use matt or satin not gloss as it just doesn't look so good when finished.
Now as chips are only normally on the edges, I lightly spray all the edges I want to chip up, using several thin coats. One heavy coat to save time is a real no no as it can run or pool along the edge and then needs sanding back, so go nice and slow apply say three light coats or as many as are needed till the edges are covered. Avoiding overspray is not such a worry as this will all be painted again, but if you are just chipping a small area mask up the rest to avoid it, and when done leave for several days to properly dry off.
When the paint has fully dried, and with most modern car paints this is overnight, but some brush on paints can take several days to go proper hard, so leave it accordingly, it's then just a simple case of rubbing off the latex.
I normally use a piece of plastic for the harder edge (don't use metal it's too hard and will take the silver off if you're not careful) then run it along breaking the paint up on the latex, then I rub it with my thumb to remove it fully.
At this point you can also use very fine wet and dry sand paper to feather the edges if you want, it really depends on how closely it will be looked at.
As I said this will also be made to look dirty which I use coal dust finally ground as it leaves a nice dirty look when rubbed off, but if you just want a slightly dirty look, I dab my thumb in coal dust then rub it along the edges repeating till it has the look I want.
If you're going for heavy handled looking dirty remember only to dirty bits you would actually touch if this was real.
I often get asked to make things that are chipped and old looking, or just how to get that chipped look, and find it surprising there aren't more tutorials around. I have found a couple, one required a great amount of skill with a brush and airbrush, and one that involved mustard, but that is only good for small models, so thought I would show you how I chip mine.