A “natural metal finish” on a plastic model doesn’t work without the “panel shading.” This means that different panels reflect light differently, because the different pieces of aluminum sheet that make up the aircraft skin are different colors. Slightly. Very slightly.
So what’s a good way to reproduce this effect? One way is to mask and spray the different panels slightly different shades. But because I’m not spraying I have to invent a new way. Here’s one approach.
I take “low tack” masking tape and then try to rub off the glue by drawing it between my fingers. This makes very low tack tape.
I grind a charcoal pencil into some sandpaper and pick up a little of it on a soft brush. Then I brush the powdered charcoal onto the model. If you can see it happening, THEN YOU ARE PUTTING ON TOO MUCH. Keep it subtle.
I tried using regular graphite pencil and got carried away and put on too much in my first try. So I had to get out the paper towel and a cotton swab with a little water and scrub it off. If you think this is easy to remove, just goof it up and find out the hard way.
Once I settled down, used the proper charcoal pencil and brushed it on LIGHTLY– I got reasonably good results.