On paper you paint the background first and the details on top. On a polycarbonate shell it is the other way round. You are looking at the paint through the plastic, so the first coat you spray is the one nearest your eye, and everything after it sits behind.
What a finished shell looks like in section
Rule one: dark before light
A dark colour will show through a light one that sits in front of it. Spray yellow, then black behind it, and the yellow turns muddy green-grey. Spray the black first, in its own masked area, then yellow over the back of everything, and both stay clean.
The usual order is black, then blues and purples, then reds and greens, then orange, yellow and white last.
Rule two: back everything
Hold a freshly painted shell up to a window and you will see daylight through most colours. On the car that looks thin and patchy, and you can see the battery through the roof. Backing coats fix it.
| Colour on the shell | Back it with | Why |
|---|---|---|
| Fluorescent | White, two coats | Fluorescents are almost transparent. White makes them glow; anything darker kills them. |
| Yellow, orange, light blue, pink | White | Keeps pale colours clean and bright. |
| Metallic and pearl | Silver for bright, black for deep | Silver reflects light back through the flake. Black gives a darker, richer shade. |
| Candy and translucent | Silver or a metallic | A candy is tinted clear; the sparkle comes from what is behind it. |
| Chrome | Black | The mirror effect only appears with black behind it. |
| Red, dark blue, green | White, or straight to black | White gives a brighter shade, black a deeper one. Choose the look you want. |
| Black | Nothing | Already opaque. |
One can of metallic blue gives three different cars: bright and silvery over silver, true to the cap over white, and deep midnight over black. Spray three stripes on an offcut from the shell and back each one differently before you commit.
Rule three: black last, and only after the backing is dry
A final coat of black over the whole inside makes the shell opaque and gives a tidy, uniform inside. Let the white or silver dry fully first. Black sprayed onto wet white can soak through and dull the colour in front.
A worked example: blue and white with a fluorescent yellow stripe
- Mask everything except the blue areas
Blue is the darkest colour, so it goes first. Three or four mist coats.
- Unmask the yellow stripe and spray it
Fluorescent yellow goes over its own area and over the back of the blue, where it cannot be seen.
- Unmask the white areas and spray white over everything
This one coat does two jobs: it is the white part of the design and the backing for the fluorescent yellow.
- Finish with black
Once the white is dry, two light coats of black over the whole inside.
Fades
A fade is two colours overlapping in mist. Spray the darker colour from one end, letting it thin to nothing across the middle of the shell, then spray the lighter colour from the other end across it. Keep the can further away than usual, around 30cm, and build it slowly. Cans can do a simple fade; for a controlled one an airbrush is the right tool. See Airbrushing an RC body.
All the backing colours are on the spray paint shelf.