Colorimetry
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Colorimetry is the science that describes colors in numbers, or provides a physical color match using a variety of measurement instruments. Colorimetry is used in chemistry, and in industries such as colour printing, textile manufacturing, paint manufacturing and in the food industry.
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[edit] Using a colorimeter
A colorimeter is the device used in colorimetry. To use this device, different solutions must be made, and a control (usually a mixture of distilled water and another solution) is first filled into a cuvette and placed inside a colourimeter to calibrate the machine. Only after the device has been calibrated can you use it to find the densities and/or concentrations of the other solutions. You do this by repeating the calibration, except with cuvettes filled with the other solutions.
[edit] Instruments
A colorimeter takes 3 wideband readings along the visible spectrum to obtain a rough estimate of a colour sample. For critical colour matching a spectrophotometer that takes readings 31 times along the visible spectrum would be employed. A densitometer is sufficient to measure lightness and darkness. A spectroradiometer measures the colours of light sources.
[edit] Range of challenges in colorimetry
Colours that look the same seldom have the same spectral characterisitics in any colorimetric system you employ, even assuming identical viewing conditions and identical observers with normal colour vision.
[edit] The measurement devices - in depth
Initially, the size of the filter chosen for the colorimeter is extremely important, as the wavelength of light that is transmitted by the colorimeter has to be same as that absorbed by the substance. Color can be measured using a spectrophotometer, which takes measurements in the visible region (and a little more on both ends,) of a given color sample. The spectral reflectance curve is the most accurate data that can be provided regarding a color's characteristics. However, a spectral reflectance curve is a graph of 31 readings taken at 10 nanometer increments along the electromagnetic spectrum from 400 to 700 nanometers. The plot is often referred to as the DNA of the colour. However, what practical application do 31 values have? This is why the values are mathematically reduced to 3 values via a calculation that integrates the "standard observer" and your chosen light source, ending up with 3 tristimulus values, which need to be converted yet again into coordinates in the desired color space.
Colorimetry utilizes the standard color science calculations provided by the International Lighting Standards Commission (CIE) in 1931. Colourimetry is not an exact science due to the limitations inherent in the system (metamerism being the most troublesome), the design of the measurement devices, the values used to estimate a given light source, etc.
