The critical role of laboratory consumables

The consumables used in vital footwear tests can greatly affect the results, as this article explains.

Ensuring reliable, accurate and repeatable testing relies on many factors, not least the quality of any reference materials or consumables associated with the test method. However, the importance of using appropriate, tightly specified and controlled reference standard materials is often overlooked or misunderstood.

What are reference standards?

For the purposes of this article, a reference standard is an example of a ‘consumable’ that is used as part of the test procedure in many footwear and material standards. The use of a consumable can range from a ‘control’ material against which the performance of the test sample is compared, through to a material which is an integral part of the test machine or procedure.

These materials are necessarily carefully specified in the relevant test methods, and such specifications must be complied with if the test results are to be reliable and correlate well with other laboratories. Of course, no documents are ever totally free from errors, and there have been instances of problems in material specifications in published test methods. However, these anomalies should become apparent when the consumables are checked – as discussed later in this article.

Fitting a test tile into a SATRA STM 603 slip rig

Examples of common 'consumable' materials are:

abradant cloth (or paper), supporting felt and backing foam for Martindale abrasion
control rubber and abrasive paper for solings abrasion
calibration rubber, abrasive paper and flooring surfaces for footwear slip resistance
control cloth and blades for glove cut testing
colour transfer pads and fabrics for rubbing, water and perspiration fastness
‘grey scales’ used to assess colour changes
analytical reagents used in chemical testing
lamps for light fastness and ozone test chambers.

This list is far from exhaustive, but it clearly demonstrates the wide ranging role these materials play in the performance of so many common test procedures. Whatever their role, if these materials do not conform to the specifications required by the test methods, the test will either not proceed correctly or the result will be incorrectly interpreted. Test results will therefore be unreliable, highly variable or both.

Specification checks essential

Whenever new supplies of consumable materials are delivered to a laboratory, it is essential that they are checked before use. Indeed, if the laboratory is working to a formal quality management system (for example, as recommended by SATRA or ISO 17025), it is a requirement that all consumables are fully ‘controlled’. This means that they have to be registered (along with all relevant details such as the supplier, delivery date, batch number, grade or quality and shelf life if relevant), marked with their name, delivery date and batch number and then checked in some way to ensure that they conform to the specification. Evidence of this conformity must also be recorded.

Reputable suppliers will ensure that all their consumables are supplied with a ‘Certificate of Conformity’ or ‘Certificate of Traceability’. When the supplier is known to be reliable, these certificates can be used as evidence of suitability. The best way to establish reliability is to conduct random in-house checks on the consumable supplier’s materials. The frequency and scale can be reduced if all checks yield good results. Conversely, they should be increased if problems are found.

Where certificates are not available from suppliers, the laboratory’s quality management system will require specification checks on the delivered materials. However, if the packaging displays information confirming that the materials conform to a relevant standard or have particular properties then the packaging itself (or a copy of it) may be used in lieu of a formal certificate when backed up by periodic testing as described above.

Test methods vary

It must be remembered that the requirements for consumables are specified in the test method. It must not be assumed, however, that if a laboratory is carrying out similar test procedures to two or more different methods (perhaps required by different customers), then the requirements for the reference materials are the same for all. It is very often the case that similar methods will have different specifications for the consumables, which makes it essential that the materials are checked against all the relevant specifications.

A good example of this may be found in the requirements for the Martindale abrasion supporting felt. There are three commonly quoted test methods for Martindale, all of which have slightly different requirements, as shown in box 1.

Box 1: Differing requirements for Martindale supporting felt
Test method	Specified thickness (mm)	Specified mass per unit area (g/m²)
SATRA TM31	2 - 3.5	575 - 800
EN ISO 12947-1	2.5 ±0.5	750 ±50
EN ISO 20344	3 ±0.5	750 ±50

Although it is possible to acquire felt which meets all three specifications, it is essential that each batch is checked against the requirements of the method or methods which are being performed in the laboratory.

Counterfeit materials common

In recent years, SATRA has become increasingly aware of the proliferation of poor quality or counterfeit reference materials being widely sold in many countries. Some consumables are inherently expensive to produce to tight specifications, and where these materials are offered at lower prices, they find a ready market among budget-conscious laboratories. If checks are not made, sub-standard materials could contribute to incorrect results.

The use of cheaper, non-compliant reference materials is a false economy. This is because the resulting unreliable results could easily lead to good quality products being rejected from production, or poor quality materials being passed for finished product use (which could subsequently not pass another test or even fail while being worn). Both of these outcomes could be very expensive for the manufacturer in terms of both financial losses and growth of a poor reputation.

It is important to always use high quality consumables to ensure accurate test results

Storage and care of consumables

Being such a valuable and necessary resource, laboratory reference materials must be stored correctly. For many, this will mean keeping them in a cool, dry and dark environment to prevent damage from excessive heat, moisture or light. However, the best conditions for each will depend on the type of material. Most materials may be stored in the controlled environment of the laboratory.

Laboratory staff must also be aware of any limitations on the shelf life of these materials. While fabrics and abrasive papers will remain in good condition for many years if stored correctly, rubber materials are prone to ageing and will have specified time limits on their usage. This ageing may be slowed by storing at lower temperatures, but expert advice must be obtained about any effects this may cause. Also, lamps used in test equipment will always have recommended maxima on their hours of use, as their light output will diminish with use. Reference standard chemicals may require additional safety measures for their storage, as these may be toxic, flammable or highly reactive. Whatever the material, reputable consumable suppliers will be able to advise on storage conditions and SATRA is always willing to help in this respect.

SATRA quality consumables

SATRA can help laboratory staff with all aspects of this important area of laboratory testing. Advice can be given on the requirements, use, storage and expiry of all reference materials and other consumables.

Most importantly, however, SATRA can supply many different consumables for a wide range of tests applicable to leathers, textiles, rubbers, footwear, leathergoods, gloves and many other consumer, as well as personal protective equipment (PPE) products. SATRA consumables are ‘second to none’ – manufactured to quality standards, as well as checked and certified (where applicable) before despatch, with relevant certificates supplied with each order.

Purchasers of SATRA consumables can be confident that the materials they buy have benefitted from SATRA’s extensive research programme and our many years’ experience of test method and machine development, coupled with the experience of testing in our own laboratories.

How can we help?

Please contact test.equipment@satra.com for more information or to order consumables.

Publishing Data

This article was originally published on page 36 of the January 2019 issue of SATRA Bulletin.