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Judging a Grease by its Color: Is ‘what we see’ an appropriate grease-evaluation method?

Although an important feature of every grease, color does not typically impart any performance properties. Color can, however, indicate the presence of certain grease additives, and the grey to black range can especially be indicative of additives used in certain industries. Additionally, some customers request certain colors of grease be used simply to tell them apart from one another within a large piece of equipment. That being said, color is still used as an indicator of a product’s quality by many end users.

When a grease appears to be ‘off-color’ to the eye, it is thought to be contaminated or possibly lacking a key component in the formulation. It may even be deemed unfit for use. What experts have found about the color of grease, however, proves this method to be flawed. In fact, when most color concerns arise, they are often due more to the quality of the evaluation method rather than a quality-related product issue. Surprisingly, eyeballing two samples to compare their color remains the most common way a customer evaluates a grease’s quality. Without question, this old school, industry-wide approach leaves much room for errors and inconsistency.

Beyond differences in grease physiology, the environment in which an object is viewed can greatly impact how color appears to the viewer. Most notably, the type and angle of light illuminating the object make a substantial difference. Although the human eye is a wonderful apparatus, it is not the most reliable tool for making important decisions based on color. What then IS the best method?

The Quality Control team at Chemtool Incorportated has been incorporating the use of the Hunter ColorFlex instrument to adjust in-process production batches to meet required color specifications, as well as to address questions about color that arise. The ColorFlex tool uses a small sample (about 25-30 grams of grease) and provides a detailed report of data in about three minutes.

The device is based on the Hunter Color theory, which laid the groundwork or the Hunter L, a, b color space. The basic methodology objectively assigns numerical values to three elements of a color. Using this method, every color can be converted to numerical values.

The implementation of the ColorFlex test has dramatically decreased color-related questions (about 70% in the first year), eliminating customer color concerns and providing drastic cost-savings by eliminating resources and manpower previously used to remedy the questions by providing hard data.

With issues relating to grease color remaining prevalent in the industry, it appears the use of the Hunter ColorFlex tool should be a serious consideration over an ‘eyeball evaluation.’

Information provided by Andrew L. Heimer. Chemist and Research Manager at Chemtool Inc., a subsidiary of Lubrizol Corp.

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