Summary of Sampling Methods for Wash Colorfastness Testing

Washing fastness test is to simulate the color firmness of textiles in different detergents and washing environments. There are many methods for testing the color fastness to washing in laboratory. Different methods may have some differences in temperature, washing liquids, and drying procedure. For large-scale testing institutions, color fastness testing adopts a multi-post process-oriented working mode, which is usually divided into sampling post, testing post, and rating post. Therefore, even in the same testing method, different inspectors will be influenced by their own habits, subjective judgments and other factors in sampling techniques, leading to some differences in test results. This paper intends to discuss the consistency of sampling methods.

A sampling of wash fastness should first take into account lining fabrics. Taking GB/T 3921-2008 as an example, this standard stipulates that the choice of lining fabrics can be multi-fiber lining fabrics or two single-fiber lining fabrics.

The multi-fiber lining fabrics include:
  • Multi-fibre lining fabrics containing wool and vinegar fibers (tested at 40℃ and 50℃ and in some cases at 60℃, which should be noted in the test report).
  • Multi-fibre lining fabrics without wool and vinegar fibers (some tested at 60℃ and the rest of them tested at 95℃). Single fiber lining fabrics are made of cotton, wool, viscose, polyamide (nylon), polyester (polyester), polyacrylonitrile (acrylic), ramie, silk, and vinegar.
Routine testing samples used in a laboratory are generally divided into samples of solid color, samples of dyed fabric, prints samples, unevenly-and gradually-colored dyeing samples, embroidery samples, beads, samples of heat-melting rhinestones, yarn and loose fibers, hollow fabrics and so on. Taking the test of multi-fibre lining fabric as an example, the sampling methods of different types of samples in the washing fastness test are analyzed in detail.

Solid Color Samples

According to the requirement of standard sample size, a specimen is randomly cut along the warp or weft in the direction of the front of the fabric. However, it is required that the sample be obtained from an evenly-dyed, wrinkle-free sample that represents a bulk sample of batch-wise staining, and not less than 10 cm from the edge of the cloth, so that the whole working surface can have a level dyeing during the test.

2 Dyed Fabric Samples

According to the standard for sample size, a specimen is required to contain all the colors of the sample. If it fails, the size can be determined in light f the proportion of the colors of the sample. Priority is given to conduct a test on the dark part or add the number of specimens, generally speaking, the increased number no more than three groups.

Prints Samples

This kind of product is characterized by its rich color. Prints samples include small prints, large prints, and interchromatin stripes. The basic principle of sampling requires that all colors should be taken by digging, and in this process, the same color parts around the specimen need to be retained as the original sample for rating and comparison. If a sample can not contain all colors, it is necessary to add more specimen or determine the number of specimen according to the proportion of each color. Dark color test is the top priority. The following is a detailed analysis of various samples.

Small prints of single circular

For single circular small prints, the sampling must be taken on a complete print as far as possible, because sometimes the pattern of same prints will have a certain color difference due to the influence of color paste prescription, prints process, and fabric structure. The method of digging shall be adopted in sampling. When digging, attention should be paid to retaining the same color around the sample as the original sample for a post-test rating and comparison.

Non-circular irregular fully-covered prints

This kind of sample is rich in color. Before sampling, we should observe the sample carefully and select the specimen from the part where the dyeing is uniform and representative for digging. Often, a single specimen cannot contain all the colors, and more are needed.

Non-circular large prints

In the sample submitted by customers to check such as sheets, quilt covers, etc., this kind of samples are characterized by a larger margin and larger prints. As each pattern has different colors, a specimen is not able to cover all colors. In this case, it is preferable to dig a specimen at the place where the color is relatively dark. In addition, we should take into account the proportion of shades of different colors in the sampling process. Only digging out the dark places is not enough. Because there may be light and dark color migration during the test process, both the staining of the sample and the changes in the specimen’s colors should be considered.

Circulating large prints

Samples of this type are usually richly colored in a circular. It is enough to dig a specimen on a circular pattern. If other colors are unavailable, more specimens may be needed.

Samples of Interchromatic stripes

Specimen should include the colors of all strips within the specified sample size. Colorfastness to washing is a rolling test, different from that to perspiration, which is static test. There is no prescribed pressure requirement. Not subject to the direction of the strip, a specimen just need to take all colors. If a sample fails, it is necessary to add more specimen or determine the number of specimen according to the proportion of each color and take the relative dark part as the priority for testing.

4 Unevenly and Gradually Colored Dyeing Samples

Generally, the colors of such samples change naturally from light to deep or from deep to light. Usually, there are two or more gradients. A specimen should be obtained from evenly dyed areas by digging in the light and deep places. Attention should be paid to avoiding some place of intermediate color gradient where the color is usually uneven and unrepresentative, and easily affects the test results.

5 Embroidery Samples

Embroidery and decals samples are combined with the base cloth by connecting wires, which are uneven. But washing test is dynamic and does not affect the test results, different from colour fastness to perspiration that has certain pressure requirements in the testing process. Sampling should include all the embroidery and background parts. Attention shall be paid to ensure that the embroidery and small parts are able to avoid falling off during the test after the samples are cut.

6 Samples of Beads and Heat-melting Rhinestones

In daily use, consumers often encounter some troublesome problems, such as heat-melting rhinestones peeling off after being washed and the color of beads touching other parts of clothes. According to some enterprise standards, assessment of the discoloration of these parts and whether they fall off and so on are required. Therefore, in accordance with the requirements of customers or the principle of strict assessment, sampling shall include all pieces of beads and heat-melting rhinestones, and ensure that the pieces that are dug do not fall off during the test.

7 Samples of Yarns and Loose Fibers

When the sample is yarn or loose fiber, if the conditions allow, a laboratory can knit yarn into fabric and sample it according to the way of fabric. Or when the sample is yarn or loose fibers,  yarn or loose fibers will be taken in the quality that is about half of the total quality of the lining fabric, and be in the form of the sand bundle so as to suit the lining fabric (figure) for testing.

8 Samples of Ribbons

There are two kinds of specimens, larger than or smaller than the lining fabrics. When sampling, the sample contains all the ribbons. If the sample size is larger than the size of the lining fabric, the sample needs to be trimmed to match the size of the lining fabric.; Otherwise, several samples need to be stitched together to match the size of the lining fabric.

9 Samples of Lace, Water-soluble Lace and Cutout

 

There are usually some prints on this kind of samples. On the premise of meeting the sampling requirements of prints samples, attention should also be paid to cutting the parts with dense fabric structure as far as possible to prevent the samples from dispersing during the test.

Matters Needing Attention

  • The test surface of the color fastness to washing must be the front of the fabric or garment.
  • When the specimen is cloth, it is required that the sample be obtained from an evenly-dyed, wrinkle-free sample that represents bulk sample of batch-wise staining, and not less than 10 cm from the edge of the cloth, so that the whole working surface can have a level dyeing during the test.
  • A specimen should include all colors as far as possible. If it fails, the relatively dark place can be preferentially cut according to the proportion of each color (the dark place should be confirmed by at least three inspectors) or conduct sampling of multiple group, but generally no more than three. When different types of samples intersect, their own sampling principles shall be met.
  • In the use of the digging method to sample, attention should be paid to retaining the same color parts around the specimen as the original one for a post-test rating and comparison.
  • In case of samples that are easy to fall off during the test, they should not be used so as to prevent the samples from falling off during the test.
  • When sampling, it should be noted that the size of the samples should be consistent with that of the lining fabric, and should not be larger or smaller? Then the size requirements specified by the lining fabric.

 

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