To find out the hidden operator errors in rubbing fastness tests that cause failures in textile testing. This guide explains the real lab mistakes, mechanical issues, uncontrolled wet pickup, and rating problems, with practical solutions to improve the accuracy, avoid rejections, and meet both ISO and AATCC buyer expectations across the labs worldwide.
Introduction to Operator Errors in Rubbing Fastness Tests
Textile testing plays an important role in maintaining the quality of clothing. Two laboratories do textile testing. The in-house laboratory does the first one, and another one is done by the 3rd party laboratories.
There are different types of textile testing, such as fiber analysis, colorfastness, chemical tests, and shrinkage tests, which play an important role. Among them, the rubbing fastness is peerless due to its practical effectiveness.
The rubbing fastness test procedure is not particularly difficult, but it has some technical issues, such as conditioning, wet pickup, and applicability. In the 3rd party laboratories, technicians are trained frequently to avoid technical and methodical errors. Their long-time expertise also helps them a lot to avoid the errors in rubbing fastness tests.
But the in-house laboratories, due to their lack of experience and resources, might have some common rubbing fastness errors. In this article, we will learn about the common operator errors in rubbing fastness tests. We will also know how to avoid them.
Why Rubbing Fastness Failures Occur in In-House and Third-Party Laboratories
In several cases, the failures of the rubbing fastness are not caused by the chemistry of the dye or fabric construction. Still, they are instead the result of common operator errors, including mechanical inconsistencies or poor laboratory practices. These issues usually occur in in-house testing laboratories where technicians may lack proper training, regular testing, or exposure to buyer-level evaluation expectations. Understanding the below operator error while testing rubbing fastness is essential for improvement of the test repeatability, ensuring compliance with international standards.
Common Operator Errors in Rubbing Fastness Tests
Poor Circular Image with Uneven Dye Pick-Up
During the rubbing fastness evaluation, the shape, uniformity, and distribution of the dye on the crocking image are critical indicators of test validity. A poor circular image with uneven dye pick-up and transfer can mislead the evaluator into assigning an incorrect rating, either falsely downgrading a good fabric or masking a genuine fastness problem.
We can place the error in the first position, which happens due to the rubbing machine’s finger on the uneven surface. If this problem occurs, the operator needs to resurface the rubbing finger on the softback waterproof abrasive paper.
Here, we should focus on the quality of the softback waterproof abrasive paper, commonly known as emery paper. It should have the perfect grit to provide enough friction without damaging the test sample. It should not be finer than 500 or P1000 grit.
Double Elongated Image
The double-elongated image appears oval rather than round. To get the accurate rating of the rubbing fastness test, the crocking cloth should be rounded. Due to looseness of the clip, the shape becomes elongated.
double elongated imageNot only does the shape become elongated, but it also becomes uneven, which is not perfect for the accurate rating. To resolve this problem, we should replace the rubbing clip and rerun the test.
Stretched and Streaked Crock Image
A stretched and streaked crock image means the stripe-like hairlines cover the entire crock square circle. It occurs when the crock is mounted square diagonally. When the crock square is mounted diagonally, it folds, causing hairlines.
It is a common operator error in rubbing fastness tests. If this problem occurs, it is not possible to rate the test. To correct the error, reset the crock square and rerun the test. Also, the operator must be careful during the rubbing test.
Scuff Mark on Rubbing Cloth
A scuff mark occurs on the side of the crock square. It occurs due to the downward position of the wire clip. It is also a common operator error during the rubbing fastness test.
To skip the error, the wire clip should be mounted in the right position during the test. The operators should be aware of the problems and perform the test accordingly to resolve the.
Scuff markStreak in the Center of the Crock Square
Streak in the center of the crock square is one type of mechanical problem. It also occurs in the direction of the rubbing track. Generally, it occurs due to the damage to the metal base of the device. If these problems occur, the device should be maintained.
Other Errors and Eradication
Sometimes, the rubbing finger is off-center during the test. In this case, the operator should adjust the position of the specimen holder on the base.
Sometimes the emery paper on the tester base needs to be replaced when it becomes smooth. Sometimes, sample slippage occurs during the rubbing fastness test. In this case, the operator should change the emery paper with the new one.
Sometimes ridges or bumps occur during testing. Also, in this case, new abrasive paper should be installed with a new one.
To get rid of all these errors requires a combination of operator awareness, routine equipment check, the selection of the right machine, and adherence to standard operating practice. Labs that implement regular internal and external audits and training programs significantly reduce the occurrence of such hidden errors.
Technical Errors in Rubbing Fastness Tests
Now we will know about some technical operator errors in rubbing fastness tests.
Wet rubbing fastness testing is more sensitive than dry rubbing, totally dependent on wet pickup accuracy control. Exceeding the required wet percentage alters the amount of moisture or humidity available to dissolve and transfer the dye, leading to either exaggerated or understated staining results. Maintaining a pickup range of 95 to 100 required both practical experience and technical skills. The operator should understand the absorbency of the fabric, the behavior of the fabric, and timing control. Rushing the wetting step will cause significant variability and undermine test reliability.
Wrong Wet Pickup Percentage
Sometimes the operator becomes hurried to do the test. In this case, the main problem occurs in the wet pickup percentage. The wet pickup percentage should be 95-100% during the rubbing fastness test. But when the operator is in a hurry, he may skip the actual wet pick up. In this case, we will not get the actual rating. So, it is very important to maintain the actual wet pickup during testing.
Sometimes the operators don’t have the proper training on the rubbing fastness test. Maintaining the actual wet pickup is a technical issue. It is not so easy to make it actual. So, frequent training is required to remove the error.
Wrong Rating
Wrong rating is also a common rubbing fastness error. To ensure the accurate rating, proper training is required. An experienced rater should rate any critical rating. Before rating, three layers of crocking cloth should be placed under the tested specimen.
Incorrect rating is one of the most damaging errors in colorfastness to rubbing testing because it directly affects decision-making, and you can reprocess a well-fasted fabric based on a false conclusion, even when the testing execution is correct. Improper evaluation against the gray scale can lead to a wrong conclusion. Light source, evaluator experience, and background setup can influence rating accuracy, and I will suggest rating the testing specimen in a dark room in a light box. To maintain professional practice, the borderline or critical rating must be confirmed by an experienced person, multiple evaluators, or with the help of a spectrophotometer to minimize subjectivity.
Incorrect identification of the front and back of the crocking fabric is a frequent but underestimated error in rubbing fastness testing. Accuracy in identifying the face and back requires both construction knowledge and processing awareness. The operator should be trained to recognize the woven construction and weave characteristics.
Sometimes the operator can’t recognize the face and back of the sample when it is a fabric. Some fabrics are very difficult to recognize their face and back side, like plain weave, taffeta, and rib fabrics. In this situation, the operator should discuss it with a technical person or contact the vendor to determine the front and back sides.
If you know the basics of how to detect the face size of a fabric, it will help you a lot to recognize it. First, you need to detect the finished part of the fabrics. If you can detect, it is the size of the fabric. The finished part’s hand feel will be smoother than the unfinished part.
Another way is to detect the upper pin mark of the fabric selvage from the stenter machine. It is the face side. But sometimes this technique does not work. Then you need to look for the ridges of the fabric. It is the most technical point to detect the fabric’s face side. You need to know the ridges of different twill fabrics, such as satin, sateen, and herringbone. It will help to detect the face side of any twill fabric.
In a wrap-up, we can say that the rubbing fastness test is a very technical test to get the accurate staining result. Proper training and technical knowledge about the rubbing fastness test are very important. Also, it is an important test for the manufacturer’s in-house laboratory and a third-party laboratory.
Conclusion
In short, the rubbing fastness test is not only a routine physical quality control procedure but also a technically very sensitive evaluation that requires precision, consistency, and a trained laboratory technician. Most of the rubbing fastness failures are attributed to the fabric quality of the dye, but in reality, the result is avoidable technician errors or machine-related issues. You can address these issues through proper training, routine maintenance, and strict procedural discipline, thereby improving the reliability and confidence in reported testing results.
For in-house testing laboratories, bridging the skill gap working with third-party laboratories requires specific training, internal audits, and practical exposure to buyer expectations and testing the same testing specimen in the in-house lab and third-party lab and comparing the results, which helps to find out the issues. By eliminating usual operator error in rubbing fastness testing, the lab can ensure accurate staining results, reduce disputes, and maintain strong compliance with universal textile testing standards.
FAQs
What are the most common operator errors in rubbing fastness tests?
Improper mounting of the crocking cloth, inaccurate wet pickup, worn rubbing finger, inaccurate rating techniques, and misidentification of the front and backside of the crocking cloth are the most common operator errors.
Why is rubbing fastness considered a high-risk textile test?
Rubbing fastness is directly related to color transfer, while wear and handling, which lead to frequent buyer claims and complaints.
How does uneven rubbing of the finger surface affect results?
It will cause uneven transfer of the dye and invalid staining patterns, which leads to incorrect grading.
What is the correct wet pickup percentage for wet rubbing fastness?
It depends on the testing procedure; for example, the 100% wet pickup is required for ISO 105 X12, while 65±5% wet pickup is required for AATCC TM8.
Can scuff marks be rated in rubbing fastness tests?
No, the scuff marks indicate the mechanical interference and invalidate the test.
Why do in-house labs face more rubbing fastness errors?
Improper or limited training, lack of the regular proficiency testing and an insufficient maintenance practices are the main reasons.
How often should abrasive paper be replaced?
Whenever the surface becomes smooth, worn, or contaminated and the gripping power is lost, the abrasive paper must be replaced.
What causes elongated crocked images?
Used or loose crocking cloth clips during mounting are the main cause of an elongated crocking image.
Is face and back identification important in rubbing fastness testing?
Yes, the wrong testing side can completely change or alter the results.
Can a test with streaked crock images be rated?
No, there must be retesting, or the test must be rerun.
Why is experienced rating important?
Because the subjective rubbing fastness evaluation requires trained judgment, and if you are using the spectrophotometer for evaluation, the instrument operator can easily give a rating with the help of the spectrophotometer.
How can laboratories reduce operator errors?
By providing the regular training to the lab technician, internal audits, and strict adherence to standard testing procedures.
Are rubbing fastness failures always due to dye problems?
No, many factors can alter the testing results rather than the chemistry of the dye.
Related Resources
Insights to Colorfastness to Rubbing/Crocking Test
Test Procedure of Rubbing Fastness Test Using JIS Standard Crockmeter
Crockmeter/Rubbing Colorfastness Tester
What is Color Fastness to Rubbing and Test Method
ISO 105-X12 vs AATCC 8: Key Differences Every Lab Manager Must Know