Colour Considerations: Managing visual expectations for metal coatings

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Metal coatings have not only improved in terms of function, but also in general esthetic—a wider range of colours and effects are now available.

Applicators and application methods
Colour-matching problems are also common when multiple coating applicators are used. The methods of applying paint—and the equipment used to do so—can vary widely between them. Another variable is the shape of the metal substrate. The coil-coating process produces colours that look different from extrusion coatings, even when the formulations are exactly the same.

Operating conditions at the time of manufacture can also affect a coating’s final appearance. Temperature, humidity, the curing process, and how thick the coating is applied are variables that can fluctuate daily, even within the same plant. Colour differences can also be attributed to the line operator.

To minimize the potential colour differences related to these variables, architects and contractors should adhere to the following guidelines:

1. Limit the number of coating applicators used on each project. Lessening the suppliers reduces the chances for colour-matching and quality problems.

2. Once coating applicators have been selected, notify the coating manufacturer of who will be responsible for which building component. This will facilitate better colour co-ordination among the different applicators.

3. Use the primary applicator panel (i.e. the major component on the building—the highest percentage of visible painted metal) as the standard. This way, the coating manufacturer can make sure the standards for each coating applicator match one another. Do not use coil-coating standards for spray coatings or vice versa. Each application method should have its own individual standard.

4. For large projects, request sample ranges from each coating applicator. Use the samples to determine the capabilities of each applicator and apply that knowledge to more effectively manage the colour-matching/co-ordination process.

5. Adjust the colour match on coil coatings to the colour of the spray coatings. Since colour control is more exact with coil than with spray coatings, it is easier to establish a colour standard with the latter, and then formulate the former to match it. The only exception to this rule is for white or light-coloured coatings. In these cases, the coil coating should be used as the template since coil coatings are usually applied at a thinner film rate, which makes them more difficult to adjust.

Spectrophotometer Support

Trying to make important choices about colour can be a highly subjective exercise. For this reason, spectrophotometers are invaluable measurement tools that take much of the guesswork out of colour evaluation. Instruments that contain integrated spheres can even sort through layers of complexity (like fabric), and eliminate gloss from the equation so only pure colour is being evaluated.While computers can never fully replace the human eye, it should be noted not every human eye perceives or sees light or colour in the same way. One reason is age. The retina contains two types of photoreceptors: cones and rods, and people begin to lose the latter with age. Rods do not perceive colour, but are acutely sensitive to light and critical for night vision. This is why a 50-year-old driver needs twice as much light to see after dark as a 30-year-old.Spectrophotometers help level the playing field when making critical decisions about quality control and design by taking the selection beyond subjectivity and physiological differences of eyesight.
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