ASTM D5386 Standard Test Method for Color of Liquids Using Tristimulus Colorimetry

 Get Certified ASTM D5386 Testing for Reliable Liquid Color Measurement 

Certified ASTM D5386 testing confirms the color rating of a clear liquid sample using a consistent, instrument-based Pt-Co scale rather than subjective visual comparison. Yellowish or brownish color variations in liquid products, including petroleum products and chemicals, are a major concern because they may indicate contamination during processing, storage, or shipment. This provides a repeatable method for evaluating the purity and quality of a liquid in manufacturing or purchasing. 

The scope of ASTM D5386 includes-

• Material type: Clear, near-clear, non-fluorescing liquid samples with no haze. 
• Purpose: Instrumental measurement of the color of liquids to rate the color based on the platinum-cobalt scale. 
• Elements analyzed: Tristimulus color values, converted to platinum-cobalt (Pt-Co) color ratings. 
• Method: Use of a colorimeter or calculation of tristimulus values from data from a spectral measurement of the liquid sample. 
• Result: A Pt-Co report value between 0 and 100 is reported, rounded according to Practice E29. 
• Test Limitations: This method is applicable to nonfluorescent liquids that have similar light absorption characteristics to those of the Pt-Co color standard solutions. 
• Environmental conditions: Consistency in lighting geometry and instrument calibration allows for accurate and repeatable tristimulus measurements. 
• Applications: Quality Control for petroleum products, purity testing for chemicals, and screening for contaminants in liquid hydrocarbons. 

What are the Uses of ASTM D5386  Testing?

ASTM D5386 testing provides a scientific, instrumentally based method of evaluating the color of liquids, rather than relying on the subjective comparison of the liquid to a color card. The platinum-cobalt scale is also a well-known reference in the petroleum and chemical industry. This standard –

• Assists with quality control for clear liquid products like petroleum and chemical materials.
• Ensures consistency in color from one production batch to the next on a standardized Pt-Co scale.
• Helps manufacturers identify contamination that causes the product to turn yellowish/brownish.
• Provides comparable results to related visual methods, such as Test Method D8005.
• Assists buyers and specifiers in checking the liquid color for purchase specifications. 

What Materials Can Be Tested Under ASTM D5386? 

ASTM D5386 tests clear, near-clear, nonfluorescent liquid samples free of haze, with nominal Pt-Co color values falling between 0 and 100. This method is frequently employed in laboratories for liquid hydrocarbons, petroleum products, and chemical liquids when the presence of yellowness is a sign of contamination from processing, storage, or shipping. Several related test methods are available for comparison, including D1686 and D2108, which cover similarly near-clear liquids by visual and instrumental measurement. Manufacturers also apply this method to solvents, plasticizers, and other clear industrial liquids where consistent color grading supports batch-to-batch quality comparisons. 

Why is ASTM D5386  Important? 

ASTM D5386 is important because it provides a consistent, instrument-based method for detecting and quantifying color changes in clear liquids, which often indicate contamination. Because liquid hydrocarbons readily absorb blue light if contaminated during processing, storage, or transport, it is important to monitor the Pt-Co color value to detect the quality problem early in the process. ASTM D5386 eliminates subjective visual comparison and helps to make more objective and repeatable quality control decisions for the petroleum and chemical industries.

ASTM D5386 Testing Process and Data Collection

There are four steps for the data collection process for ASTM D5386. First, they verify that the liquid sample is clear, not hazy, and appropriate for the instrumental color range. Then, colorimeter technicians use standard solutions of known platinum-cobalt color to calibrate the colorimeter. The instrument then measures the sample’s tristimulus values directly or calculates them from spectral transmission data. In the final step, analysts transform the tristimulus measurement into a Pt-Co color rating and round as per Practice E29. 

Common Challenges and Troubleshooting

Three common problems with ASTM D5386 testing are haze in the sample, instrument calibration drift, and sample cell cleanliness. The method is for clear, haze-free liquids; haze or particulate matter can scatter light and affect the determination of the color. Calibration drift in the instrument with standard solutions containing Pt-Co also affects the measured value over time. Residue from a previous test in the sample cell causes additional error in the test result. The solution is to pre-filter or confirm sample clarity before testing, recalibrate the colorimeter regularly, and clean the sample cell thoroughly between readings.

• The colorimeter is used to obtain a tristimulus measurement that the laboratory reports as a Pt-Co value (on the scale of 0 to 100). 
• The laboratory report reflects the color the laboratory measured with the colorimeter, which is expressed on a scale of 0 to 100 of the tristimulus measurement (Pt-Co value).
• The method for sample preparation and loading the cells, either by filtering the liquid or by ensuring that the liquid is free from haze, is decided by the technician.
• The analyst enters the tristimulus values that are measured with the colorimeter, and correlates the result to the calibration standards used in the test.
• The engineer considers the anticipated color range of the liquid, its processing history, and the potential for contamination when interpreting the Pt-Co result.
• Manufacturers use the measured Pt-Co value to support quality control and specification compliance decisions for petroleum and chemical liquid products. 

Link to ASTM D5386