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Mottled surface blemishes are often blamed on technique, air pressure, or flash time, but pigment cross-contamination is one of the most overlooked causes. When traces of dark pigment remain in a cup, fluid passage, lid vent, filter, or mixing stick, they can migrate into a light color and create cloudy patches, dirty undertones, or random specks. The opposite problem also occurs when light or pearl residue contaminates dark colors and produces a washed or uneven face tone.
The issue is especially serious in automotive refinishing because modern basecoats contain fine metallics, pearls, transparent toners, and high-strength pigments. A tiny amount of black, blue, red oxide, or coarse metallic residue can shift a white, silver, beige, or light blue formula. Once sprayed, the defect may not appear immediately. It can become visible after flash, after clearcoat, or under sunlight at a low viewing angle.
When using LVLP Spray Gun Dynamic Fan Control, Uninterrupted Dispense, the painter should treat color changeover as a controlled process, not a quick rinse. Drain the cup completely, wipe the cup wall, flush the fluid passage, remove the filter if used, and inspect the lid and vent hole. A blocked or stained vent can release old pigment during spraying. For an air spray gun, trigger solvent through the gun until the discharge is visually clean, then perform a white-card test before loading a light color.
Mixing-room discipline matters as much as gun cleaning. Use separate stir sticks, strainers, and mixing cups for light and dark families whenever possible. Keep toner lids clean and never place contaminated strainers on the bench. If a technician has just sprayed black, red, or strong blue pigment, the next light-color job should receive extra inspection before the vehicle enters the booth.
For LVLP Spray Gun Dynamic Fan Control, Uninterrupted Dispense, check the first fan pattern on a clean white spray-out card. Look for peppering, shade streaks, or uneven metallic orientation. If contamination appears, stop immediately. Do not try to bury it with extra coats. Recirculate, reclean, and reload fresh material.
The most effective prevention method is a standard operating procedure: segregated cleaning, documented gun maintenance, clean strainers, sealed cups, and a final spray-out check. Pigment cross-contamination is small in volume but large in visual impact. Controlling it protects color match, reduces rework, and preserves the credibility of the refinishing process.
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