Let’s say you want to do some of that Italian camouflage with tiny circles in 1:72 scale, but you don’t have the fine tip airbrush or the skill to use it. Here’s a method you might consider.
This was done with Testors enamel thinned with mineral spirits.
And this was the tool used to do it.
It might also be handy for things like control panels or wheels.
Don
If I want fine lines of a dark color to be used on a light color, I make a decal on clear inkjet paper. With modern decal paper and inkjet printers you can get a very fine line (and of very even width).
I make boot topping lines for modern ships this way, even though some of these are wide enough my airbrush would do them, but airbrushing does not control width well enough for that line. I just draw black lines of needed width in my photo editor program, print then on decal paper, and apply.
Gerald Voigt found the PITT Artist Pens from Faber-Castell usefule for this purpose. You don’t have to deal with the maintenance and refilling to use them. This can be a tedious process especially if you don’t use them frequently.
The PITT pens are neat if they have the color you want. The advantage of the old dip style pen is that you can use any modeling paint if you thin it enough. Cleaning is pretty easy; just dip it in thinner and wipe it off.
One reason I posted this is to point out that there are alternatives to trying to do ridiculously fine lines with an airbrush. Even airbrush artists will sometimes use pencils, brushes, or even scratching to do fine details.
Don
You could also use an ink bow, which may allow you greater flexibility than the pen nib. To an extent, you can adjust the width of the line with an ink bow.
My problem with the PITT pens is the price. For highlighting and details, I think that they have every color that I may need.
Black, Cadmium yellow, Indianthrene blue, Phthalo blue, Pink carmine, Cold grey III, Cold grey IV, Caput mortum, Leaf green, Orange glaze, Middle purple pink, Purple violet, Dark phthalo green, Magenta, Warm grey III, Raw umber, Sky blue, Ivory, Light yellow glaze, Scarlet red, Light cobalt turquoise, Cobalt green, Light phthalo green, Light flesh
They have metallic colors too which are even more expensive. I have not used the PITT, just quoting Gerald for other users.