Interested in a little light reading?

Commercial grade peanut butter

The USDA quality system assigns peanut butter quality rating of USDA Grade A, Grade B and Other based on 4 attributes that total 100 points.

Color – 20 points

Consistency – 20 points

Absence of defects – 30 points

Flavor and aroma – 30 points

All four quality characteristics are based on sensory qualification but color can be quantified.

The USDA Peanut Butter Color Standards are a set of 4 plastic chips that serve as visual guides used for defining the color of processed peanut butter defining USDA Grade A (2 to 3 Medium Brown) between too light (1 Light Brown) and too dark USDA Grade B (4 Dark Brown).

USDA Peanut Butter Color Standards

The reference document for these US Peanut Butter Color Standards is:

US Standards for Grades of Peanut Butter – February 5, 1972
Available on internet as a US Federal Standard from USDA/AMS GSA Washington, DC USA www.ams.usda.gov

Information on this method comes from:

Processed Products Branch
Fruit and Vegetable Division, AMS
U.S. Department of Agriculture
Washington, D.C. 20090-6456 USA
www.ams.usda.gov

FAQ: “You used the acronym CIE.  Could you tell me what that is? If it is a document, could you please let me know where I can access it?”

CIE stands for “Commission internationale de l´éclairage” which is the French version of “International Commission on Illumination”.

The CIE is a standards body that defines and maintains the global rules for light and color measurement. This is like the CIPM (Comité international des poids et measures) who defines and maintains metric dimensions, weights and volumes. It is composed of approximately 38 member committees from countries around the world.

The CIE rules are incorporated into industrial test methods defined by approximately 30 international industrial standards bodies, the most prominent of which are:

• ASTM – American Society of Testing and Materials, West Conshohocken, PA USA
• ISO – International Organization for Standardization, Geneva, Switzerland.
• JIS – Japanese Industrial Standards are available from JSA – Japanese Standards Association, Tokyo, Japan.

More background information is at the CIE web site and at Wikipedia.

Visual Observing Situation Model

HunterLab instruments measure the color as it relates to the quality of the product. To be able to begin to measure and quantify color we have to know more about why colors appear as they do. As humans we all see and perceive color differently; this is because the human perception of color is a psychophysical response. The visual observing situation model shown above illustrates the three components necessary for the perception of color.

The first component of the visual observing model is a white light source. This light provides the spectral energy required for viewing color, without light we cannot see colors. The next component needed in the visual observing model is an object. This object modifies the spectral energy from the light source. Colorants, such as pigments or dyes, in the object selectively absorb some wavelengths of the light while reflecting or transmitting others. The last component of the observing model is the human observer. The observer is a human eye that receives the light off or through the object and then the brain provides the perception for the vision.

In order to build an instrument that will quantify human color perception each item in the visual observing situation model must be quantified. These three items are all able to be quantified as a table of numbers.

This is a series post. We will go into further detail on quantifying white light sources, objects, and observers in subsequent posts.

Enter Standard Data window

FAQ: “Do you have a formula to calculate Hunter L, a, b values from CIE L*, a*, b* values?”

The only way to convert between different color scales, illuminants, and observers is to have spectral data for your  samples.

All Hunter L, a, b and CIE L*, a*, b* values are calculated from X, Y, Z values and chromaticity coefficients for the illuminant and observer used. Most color scales are calculated using CIE X, Y, Z tristimulus values. Spectral values from the sample measurement allow for conversion between different color scales, illuminants, and observers because X, Y, Z CIE tristimulus values are calculated from spectral values.

That being said, the HunterLab EasyMatch QC software does have the ability to convert color values assuming you are using the same illuminant and observer. To do this you will first need to enter the color values you want to convert into the EasyMatch QC software. This is done by right clicking in the Job Tree and selecting Enter Standard (or Sample) Data. Select the appropriate color Scale and Illuminant/Observer combination, enter your data, and click OK. Once you enter the Standard (or Sample) ID the values will appear in the Color Data Table.

To convert these values move the mouse to the Color Data Table, right click, and select Configure. Use the drop down menu under Scales to select the color scale you would like to convert to and use the left arrows to move it to the Selected Items list. Click OK to save your changes.

In the Color Data Table you should now see your converted color values.

AHAM pre-stained and laundered textile swatches.

Humans wear clothes and clothes require cleaning. There are basically three themes related to the removal of soil and stains.

1. Testing the effectiveness of laundry detergents and cleaners
2. Testing the cleaning effectiveness of wash machines.
3. Staining on textiles using applied or sprayed on liquids.

While information is available on how you can prepare your own soiled or stained textile swatches, it is usually more consistent and cost effective to purchase them. When purchasing, it is important to know what industry test method (AHAM, EMPA, ASTM, IEC 60356, AS/NZ) is required. Below are some suppliers of pre-soiled and stained textile swatches for testing. They may also be able to help with before and after colorimetric measurement evaluation:

Parameter Generation & Control
Black Mountain, NC 28711 USA
+828-669-8717
http://humiditycontrol.com

Testfabrics, Inc.
West Pittston, PA 186543 USA
+803-329-2110
www.testfabrics.com

DLI - Drycleaning and Laundry Institute
Laurel, MD 20707 USA
+301-622-1900
www.dlionline.org

wfk Testgewebe GmbH
D-41379 Brüggen-Bracht, Germany
+49 (-2157) -871977
www.testgewebe.de

Visual examples of metamerism.

Why do the samples above look the same under one lighting condition but different under another? These samples exhibit metamerism, which means they match under some lighting conditions but not others. This can be a serious problem for manufacturers, especially those who combine various parts of different materials or sources into one product. Customers expect all parts of the products that they purchase to match in daylight as well as under the fluorescent lights of department stores or the tungsten light of their home.

As a result of this phenomenon, a Metamerism Index (MI) has been developed. The MI is a single number index that indicates how well two samples that match under one illuminant will match under another illuminant. The MI is calculated with the ΔL, Δa, and Δb values of a sample and a standard under a reference illuminant and a test illuminant. Usually the D65 illuminant (daylight) is used as the reference illuminant. For the MI to be meaningful and accurate the samples should be a good match under the reference illuminant.

HunterLab instruments and software have the ability to measure L a b values under a wide variety of illuminants and are well suited to measuring MI values. This allows HunterLab customers to evaluate their product under different lighting conditions to ensure that their product will meet their customer’s needs.

Visual differences of preforms.

Can you see a visual difference between the three samples above? Chances are if you can see a difference between samples then HunterLab instruments can measure and quantify these variances. There are several ways to quantify differences with color measurement. You can evaluate dL* da* and db* values to see how samples vary from a standard within the L* a* b* color scale. There are also single number metrics that can be used to quantify color differences. Although dL* da* and db* values define color differences well a single number Pass/Fail measurement that defines a 3 dimensional tolerance can be helpful.

One of the most robust single number color quality metrics is dE CMC (also called delta E CMC.) dE CMC is an elliptical tolerance that was developed by the Color Measurement Committee of the Society of Dyers and Colorists. Color differences calculated using the CMC method are believed to correlate better with visual assessment than other color differences. The CMC ellipse is unique in that the shape of it changes depending on where the standard is in color space.

A dE CMC value of 1 represents an approximate visual difference for a very flat uniform surface, such as a tile. However, most sample types are not a uniform tile. What tolerances are acceptable varies depending on the application. Customers have to balance minimum perceptible differences with maximum acceptable differences in their products. The size of the dE CMC ellipse can be adjusted to the maximum acceptable limit by adjusting a factor in the CMC calculation.

In the samples above a clear visual difference can be observed. Our instruments were able to measure and quantify this difference. The product in the middle is the standard and the samples to the left and right represent unacceptable colors. The sample on the left measured a dE CMC value of approximately 19 and the sample on the left measured a dE CMC value of approximately 4. One of the major benefits of HunterLab instruments is that they are able to quantify color differences that are visually observed in products.