Liquid Color Measurement

Liquid color measurement is an important analytical technique in the fields of chemical, pharmaceutical, food and beverage, used to evaluate the quality, purity or other characteristics of liquids. Depending on the transparency of the liquid, the principle and tool selection of its color measurement are also different. This article will focus on the topic of liquid color measurement, combining the characteristics of different liquid transparency, and introduce the relevant measurement principles and tools.

Liquids can be divided into opaque liquids, translucent liquids, and transparent liquids according to their transparency. The color of opaque liquids (such as emulsions or suspensions) can be measured by reflectance, and both benchtop spectrophotometers and portable spectrophotometers can meet the measurement needs. For translucent and transparent liquids, since light will be partially transmitted, reflected, or even diffused in them, the color cannot be accurately measured by reflectance alone. Therefore, for such liquids, a measuring instrument with a combined transmittance or reflectance function, such as a benchtop spectrophotometer or a color transmittance meter, is required to obtain more accurate results.
 

Liquid Color Measurement Tools

• Reflection mode : Applicable to opaque liquids, and determines color by analyzing the reflection spectrum characteristics.
• Transmission mode : Applicable to transparent or translucent liquids, and determines color and transparency parameters (such as transmittance and haze) by detecting transmitted light.

This instrument is widely used in the food, beverage, chemical and pharmaceutical industries to meet the stringent requirements for liquid color measurement and is a powerful professional device.
 
Haze meter
The haze meter is an instrument widely used in optical performance testing. It can be used for transmittance and haze testing in glass processing, plastic processing, film manufacturing, display processing, and packaging industries. At the same time, the haze meter can also measure the transmittance of liquid samples , providing data support for the evaluation of liquid transparency and optical properties.

 

Measuring the color value of opaque liquids

• Spectrophotometer or spectrocolorimeter :
  • It is recommended to use 3nh spectrophotometer YS6060 or other instruments with integrating spheres, which can handle the light scattering problem of opaque samples and ensure measurement accuracy.

• Integrating sphere configuration :
  • Integrating spheres collect diffuse reflected light and are suitable for measuring opaque or milky samples.
  • Configuration: SCI (specular inclusion) or SCE (specular exclusion) mode.

• Liquid state adjustment :
  • If the liquid is viscous or has layers, it is recommended to stir well.
  • If possible, avoid air bubbles, as they will affect the transmission of light.
• Sample loading method : You can use a quartz cuvette to load the sample, or spread the liquid evenly on a standard base plate (such as a black and white contrast base plate).

• Perform white and black board calibration to ensure the instrument works properly.
• Select SCI or SCE mode according to measurement requirements.

• Place the sample:
  • If using a cuvette, make sure it is clean and free of scratches.
  • If smearing the sample, ensure that the sample surface is even and free of bubbles or particles.
• Select measurement parameters:
  • Select a CIE standard illuminant (eg D65 daylight) and an observer angle (eg 10°).
• Start measurement:
  • The instrument captures the spectral data of the sample's reflection or transmission and calculates color values (such as Lab * values).

• The instrument will output CIE colorimetric values (such as L, a , b or XYZ ).
  • L *: Indicates lightness, the higher the value, the brighter the sample.
  • a *: Red-green direction, positive value is red, negative value is green.
  • b *: Yellow-blue direction, positive value is yellow, negative value is blue.
• For multiple samples, the color difference between them can be calculated by the ΔE* value to determine whether the color meets the consistency requirements.

Measuring the color of translucent and transparent liquids

• It is recommended to use a spectrophotometer with transmission measurement mode (such as 3nh TS8560 ) or a haze meter (such as YH1610 ) .

• Transmitted light measurement is the mode best suited for transparent and translucent liquids.

• Use a clean, scratch-free quartz cuvette (usually 10 mm thick).
• Fill the cuvette with clear liquid, avoiding any bubbles.
• Make sure that the liquid in the cuvette does not overflow and wipe the outer surface clean.

• Select Transmission Mode .
• Set the standard illuminant (e.g. D65) and the observation angle (e.g. 10°).
• Perform white plate calibration (transmission calibration) of the instrument.

• Place the cuvette into the transmission measurement chamber of the instrument, making sure the light path is unobstructed.
• Start the measurement and record the color value of the transparent liquid (such asL, a , b or XYZ ).

• Quartz cuvettes can be used for translucent liquids, but it is necessary to ensure that the liquid is uniform and free of bubbles.
• For viscous translucent liquids, the cuvette thickness can be adjusted (eg 5mm or 10mm) to reduce the effect of light scattering.

• Select transmission mode, but use an integrating sphere configuration to reduce the effect of stray light on the results.
• Set the light source and viewing angle to match the settings for transparent liquids.

• The measurement procedure is the same as for transparent liquids, but it is recommended to take multiple measurements and take the average value to reduce fluctuations caused by scattering.

1. Cuvette selection :
   • For transparent liquids, the clarity of the quartz cuvette is very important.
   • For translucent liquids, cuvettes of varying thickness can be selected to optimize the light path.
2. Calibration and Cleaning :
   • The instrument and cuvettes must be kept clean, especially when using different liquids, to avoid cross contamination.
3. Measurement mode selection :
   • For transparent liquids, standard transmission mode is sufficient.
   • For translucent liquids, it may be necessary to enable integrating sphere mode to reduce interference from light scattering.
4. Data consistency :
   • Measuring the same liquid multiple times ensures consistent measurements and more reliable results.

• L, a , b values output by the instrument :
  • L * represents the lightness of a liquid.
  • a * indicates the red-green direction of the liquid.
  • b * indicates the yellow-blue direction of the liquid.
• For multiple samples, the ΔE value can be calculated, the color difference can be analyzed, and the consistency between samples can be judged.