Offer the bath dish first
A crimson rosella should be offered a bath regularly, and for this species a wide, shallow dish is the first choice because rosellas are keen, splashy bathers that like to get into water properly. Use a heavy, stable dish with water only deep enough to cover the bird's legs, set it in the cage or on a play stand in the morning, and leave it for a while rather than expecting an instant dive. A rosella that hops in, dips its chest, and shakes water through its wings is cleaning exactly as it needs to, and most will bathe several times a week when the dish appears on a predictable routine.
Where misting fits in
Misting is the useful second option, not a replacement forced on the bird. On days the rosella ignores the dish, during a heavy moult when pin feathers make the skin itchy, or in dry heated rooms, spray plain room-temperature water in a fine mist above the bird so droplets fall like light rain. Aim over the rosella, never straight into its face, and stop if it moves away, flattens its feathers, or tries to escape the spray; a bird that leans in, fluffs, and lifts its wings is asking for more. Never add soap, detergents, or scented feather sprays, because a rosella preens everything on its feathers back into its mouth.
Timing and drying
Bathe a crimson rosella early in the day so there are hours of warmth and daylight for the plumage to dry completely before it roosts for the night. Keep the room free of cold drafts while the bird is wet, and do not put a damp rosella back into a cool aviary in the evening. Change the bath water as soon as it is fouled, since rosellas will drink from the dish mid-bath, and wash the dish itself regularly so a slimy film does not build up. After bathing, expect a long preening session; that is the bird realigning feathers and spreading its own oils, and it is part of the benefit rather than a sign anything is wrong.
When bathing habits are a health clue
A rosella that suddenly bathes constantly and scratches may be uncomfortable in its skin or feathers, while one that stops bathing altogether during a moult may be feeling unwell, so treat a sharp change in bathing behaviour as information, not just a quirk. Look for flaky skin, broken feathers, or the bird plucking at one area, and take persistent changes to an avian veterinarian rather than misting more often to compensate. Feather condition also reflects diet and air quality, so a dull, dry rosella that still refuses water deserves a wider look at its whole routine.
Making bath day a routine
Rosellas bathe most readily when the dish arrives at a familiar time from a familiar person, so tie it to a fixed point in the morning round instead of offering it at random. KinsLe's Care Teams can list bath setup among your crimson rosella's regular duties, so whoever does the morning feed also puts the dish in and marks it done.