Why carry out a colour fastness test on your product?

Why carry out a colour fastness test on your product?

A colour fastness test determines the resistance of textile colours against specific conditions. Tests include water, light, rubbing, washing and perspiration tests to name a few. It is an important indicator to measure the durability of dyed products and helps with due diligence. As a result avoiding unnecessary returns.

 

Poor colour fastness to rubbing is predominantly caused by dye that is inadequately fixed within the leather substrate. Therefore, to create improved performance it is necessary to ensure that as much dye as possible is fixed and any excess unfixed dye is removed from the process.

 

To reduce the risk of colour transfer, it is important to ensure the dye penetrates and fixes within the leather structure. However, when creating dark colours it is necessary to build up the dye molecules on the surface to get the depth. Thus, with dark shades, the process creates a higher risk of dye transfer. Therefore, a trade off has to be accepted between shade depth and colour fastness performance.

 

In most cases, the best performance that can be expected, on a dark shade, for an aniline leather is as defined in the table below;

 

BS EN ISO 11640:2018 - Colour fastness to rubbing - Veslic

Dry

50 cycles

GSR 3/4

Wet

20 cycles

GSR 2/3

Perspiration

10 cycles

GSR 2/3

 

GSR – grey scale rating.

 

To consistently achieve these standards for a leather manufacturer will be challenging, but here are a few tips that can help improve the performance and consistency of dyeing:

 

  • The tanning and re-tanning process needs to be well engineered as these are significant factors in the fixation and build up of the dyeing process.
  • The quality of the dye used will have an impact on the performance, but good quality dyes alone will not solve a fastness problem.
  • The neutralization process must be fully complete
  • The pH and temperature of the float will need to be carefully controlled
  • Dye should be added in a way that does not overload the float, this might mean two or three additions to build up the shade.
  • The dye will need to be fixed at the end of the process and any excess dye removed from the bath through washing
  • A check of residual loose dye can be made through basic checks such as visual dye exhaustion and a squeeze test of a cutting from the drum (before the load is dropped) at the end of the process.

 

One the leather is dry there is little that can be done to a leather with loose dye. There are a few options;

 

  • Apply a light finish to the surface to fix the dye (this will change the aesthetics and may not be an option)
  • A basic solution (and last resort that can have mixed results) can be to pad/plush the grain of the leather to remove any excess dye from the surface. This may change the gloss and therefore further work may be needed if a dull effect is required.

 

Manufacturers, brands, and retailers are expected to conduct a range of performance and compliance tests to ensure that products entering the market place are safe, fit for purpose, and meet global legislation.

 

Eurofins | BLC are able to help with concerns or questions you may have about materials testing. Contact us today to see how Eurofins | BLC materials testing services can identify and reduce risks in your leather supply chain via [email protected] or telephone +44(0)1604 679999.

 

 

28 July 2021

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