Paint goes wherever it can. Masking is how you tell it where to stop, and the sharpness of every line on the finished shell is decided before the can is shaken. There are three tools for the job: the window masks in the bag, tape, and liquid mask.
Window masks
Most clear shells come with pre-cut vinyl masks for the windows. They go on the inside, after washing and drying.
- Line up one edge, then lay the mask down from that edge so no air is trapped.
- Press every edge down hard with a fingernail or the back of a spoon. The edge is where paint creeps in.
- No masks supplied? Cover the window with wide tape and trim round the moulded window line with a sharp knife, using light pressure.
Tape, for stripes and straight splits
Masking tape made for modelling is thin and has a low-tack adhesive that leaves nothing behind. Household decorating tape is too thick and too sticky for clean lines.
| Width | Use it for |
|---|---|
| 2 to 3mm line tape | Curves and pinstripes. Narrow tape bends without lifting. |
| 6 to 12mm | Edges of a colour split, racing stripes. |
| 18mm and wider | Filling in the area behind an edge quickly. |
- Lay the edge first
Run narrow tape along the line where two colours meet. Pull it gently as you go to keep it straight; let it relax on curves so it does not lift.
- Fill in behind it
Cover the rest of the area with wider tape, overlapping each strip, or with paper taped at the edges.
- Burnish
Rub along every edge with a fingernail. In corners and over body lines, push the tape right into the crease.
- Seal the edge
For the sharpest line, mist one very light coat of the colour that is already under the tape, or of clear, along the edge. Any paint that creeps under is then the colour that is meant to be there.
Liquid mask, for curves and complex shapes
Liquid mask is brushed onto the whole inside of the shell and dries to a rubbery film. You draw the design on the outside, cut it into the film on the inside, and peel away one section at a time as you spray each colour. It handles flames, scallops and lettering that tape cannot.
- Apply three generous coats
Brush or pour it on thick. Thin film tears when you peel it. Let each coat dry until it turns clear before the next; a hair dryer on low speeds this up.
- Draw the design on the outside
Use a marker on the protective film. You will see it through the shell and it peels away with the film at the end.
- Cut with a new blade and almost no pressure
You are cutting the film, not the shell. Let the weight of the knife do it. A scored shell will crack along the score.
- Peel the darkest section first
Lift it with the tip of the knife, spray that colour, let it dry, peel the next.
It becomes harder to peel as it ages. Mask and spray within a few days.
Taking masks off
- Peel tape and masks when the paint is touch dry, not rock hard. Fully cured paint can chip along the edge.
- Pull the tape back over itself at a low angle, slowly.
- If paint has bridged the edge, run a sharp blade lightly along the line first.
When paint has crept under
A little bleed can be picked back while it is fresh with a cocktail stick or the corner of a cloth. Once dry, the usual fix is to hide it: a pinstripe of line tape or a decal on the outside covers a soft edge neatly. More in Fixing paint mistakes and tired shells.
Masked up? The spraying order matters next: Colour order and backing coats.