A Muddy Red in a Fluorescent Corridor
A newly built municipal health centre in Bhubaneswar has a corridor 2.4 m wide and 18 m long. Daylight enters only from a glass door at the north end; the remaining 15 m is lit by cool-white fluorescent tubes. The medical officer wants a warm and welcoming mural on both long walls, with ochre, terracotta red, and deep green bands at eye level. A volunteer painter has already applied a sample of terracotta red on the west wall; under the fluorescent light it looks muddy brown, although it looked correct in the painter's north-lit studio. The paint is acrylic emulsion, and the wall was painted with lime wash two months ago, with slight chalkiness when rubbed. The painter has four days and a limited budget, and cannot change the light fittings.
1. Diagnose why the terracotta sample looks muddy, separating colour-appearance problems from wall-preparation problems.
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Two separate problems. First, colour appearance: the studio is north-lit, with a high colour temperature and relatively even spectrum; the corridor's cool-white fluorescent tubes have a different spectral output and a lower colour-rendering index. A terracotta mixed under one light can look muddy under another-this is metamerism plus simultaneous contrast from the green band and the corridor's grey floor. Second, the wall: lime wash is chalky and friable; acrylic applied directly may fail by flaking or efflorescence, and the brown may partly be grey lime showing through a thin coat. The painter should not judge the sample in the studio or from a photograph.
2. Describe a test-patch method and palette adjustment that would settle the choice on site.
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Prepare three test patches about 600 mm square on the actual wall: the proposed terracotta, a slightly lighter and more yellow ochre-red, and a deeper red with less black. Label them and view them at the same time of day under the existing tubes and at the north door in daylight. Step back 3 m and 10 m. Choose the patch that stays warm under fluorescent light; usually this means increasing chroma and avoiding black or too much blue in the mix. Make the eye-level band narrower and place the deepest green away from the red to reduce simultaneous contrast. Get the medical officer's approval on the wall, not in the studio.
3. Advise on surface preparation and a four-day application plan that protects durability.
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Remove loose chalk by dry brushing and scraping; wash with a dilute sugar-soap solution and rinse; allow to dry. Apply a penetrating alkali-resistant primer or a stabilising primer recommended for lime wash, then a mist coat of the mural acrylic. Avoid a fully sealed plastic film over damp lime; use a breathable system if damp persists. Keep the palette to a few pre-mixed buckets for consistency across 18 m, and note batch numbers. Protect the floor and sockets, ventilate, and keep the corridor open at one end. A four-day schedule should include one full day for preparation and one for the second coat, not just painting.