Flash

Flash is the thin, often razor-like film of plastic that seeps out along the seam of an injection mould and ends up stuck to the edge of a part. It is different from a gate mark, since flash can appear anywhere a mould has worn slightly or was not perfectly aligned when the plastic was injected, and older or budget kits tend to show more of it than newer, tightly tooled ones.

Cleaning flash up is usually a quick job with a hobby knife, a sanding stick, or a fine file run gently along the affected edge. It is worth checking parts under a strong light or magnifier before gluing, since thin flash can be easy to miss on a matte plastic surface and will show as an odd hard line once primer or paint is applied. Panel lines and rivet detail are the areas where flash removal takes the most care.

The main mistake beginners make is sanding so aggressively that surface detail, like recessed panel lines or fine rivets, gets softened or erased along with the flash. Light, repeated passes with a sharp blade or fine-grit stick remove the excess without flattening the detail underneath, and test fitting parts before final glue-up catches any flash that would otherwise stop two halves from meeting cleanly.