company news about How is the Color Fastness Rated?

How is the Color Fastness Rated?

Most of the current color fastness testing methods are conducted through simulation or comprehensive tests based on the environmental and conditions involved. The color fastness levels are determined by observing the color changes of the test samples and the color transfer on the backing fabric. What is particularly unique is that the lightfastness is rated using the blue scale, while the dry cleaning fastness is evaluated by the color transfer of the solvent. 

When evaluating the color fastness, the changes in the three attributes of color, namely hue, lightness and purity, should be comprehensively considered. Hue refers to the appearance of the color. Among the three attributes, hue can be used to distinguish colors. Depending on the different wavelengths of light, colors have properties such as red, yellow or green, which is called hue. According to the degree of light reflection from the object's surface, the brightness of the color will vary. This degree of brightness of the color is called lightness. Purity refers to the saturation of the color. The simpler the wavelength of the light wave, the higher the purity of the hue, and vice versa, the lower the purity.

The color fastness rating can be divided into visual rating and instrument rating. During the visual rating, the background should be a neutral gray, approximately between level 1 and level 2 of the standard gray card (similar to the Munsell color card N5). The lighting conditions should be clear northern daylight (9:00 - 15:00), or an equivalent light source with an illuminance of 600 lx or above. The incident light should form an angle of approximately 45° with the textile surface, and the observation direction should be roughly perpendicular to the textile surface. The color of the cover plates for the original sample and the sample after testing should be consistent, and neutral color, gray or black should be used. The size and shape should be approximately the same. The rating personnel should wear a neutral gray work uniform, and the rating process should avoid the influence of environmental color.

Color fastness rating: Compare the post-test sample with the original sample to see how close the degree of color change is to the level indicated by the gray card.

Color fastness rating: After testing, the color fading grade was compared with that of the untested fabric, and a similar grade was obtained.

Instrument rating:

The principle of instrument calibration is to use the absolute reflectance of a known standard whiteboard for calibration. It measures the spectral power distribution of the reflected light from the sample or the intrinsic reflectance characteristics of the sample. Then, based on the spectral measurement data, the tristimulus values, chromaticity coordinates, CIELAB uniform color space, etc. of the object under the standard illuminant are calculated. And through a series of formulas, it is converted into the gray card numbers for color change and color fastness.

Sometimes when reading the report, one may have doubts. Why is the test result for color fading resistance under soaping conditions shown in the report 3 levels, while the standard requires it to be ≥ 3-4? Or is the report's judgment incorrect? Is there a mistake in the report's determination?

In fact, the result determination is correct. The grade 3-4 for color fastness assessment is not a general mathematical interval; it is a series, indicating that the test result falls between the 3rd and 4th grades.

How to judge the level of strength:

Standard 1: Sunlight Fastness

The drying process in daily life is a common method for testing color fastness. Because under the sunlight, photosynthesis can activate the molecules in the dye, causing fading. Although this fading is considered ordinary, the reaction process is rather complex. Moreover, the fastness varies for different fibers, and the fading under sunlight is worse for lower concentrations than for higher concentrations. In the judgment criteria, there are also corresponding grades, divided into eight levels, with level one being poor and level eight being good.

Standard 2: Soap Resistance Rating

The soaping process involves combining water with soap powder or other laundry detergents, and then washing the colored textiles together. The fading that occurs during this process serves as the criterion for evaluating the durability. For example, in our daily lives, common items like jeans often show color fading when washed. Over time, it becomes noticeable that the color of the jeans becomes lighter and eventually they are discarded. According to tests, the reason for the rapid fading after washing is not only due to chemical reactions but also due to photosynthesis. This makes the evaluation of soaping durability a quick method for testing. In the judgment, it is divided into five levels and nine grades, with grade one indicating severe fading and grade five indicating no fading.

Standard 3: Felt Resistance to Friction

This method of evaluation is simpler compared to the soap washing fastness test. It mainly involves the friction between objects. In the experiments, this method also has two types. One is dry friction (direct friction between objects), and the other is wet friction (mainly based on the changes caused by reacting with water). Dry friction means taking a piece of white, un-dyed fabric and rubbing it against a dyed textile item. If there is color on the white fabric, it indicates that the color fastness of the dyed textile is not high, and the darker the color, the lower the color fastness. Therefore, if the general public buys textiles, they may consider using dry friction for evaluation. In the judgment, it is divided into five levels, with level one indicating poor fading and level five indicating no fading at all.

The above methods are all convenient ways to determine the color fastness in daily life. If conditions permit, tests can also be conducted using the "gray fading sample cards" as per the national standards for rating.