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Colour Fastness Evaluation And Effecting Factors
2019/09/05
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Colour fastness is the resistance of a material to change in any of its colour characteristics, to the transfer of its colourants to adjacent materials or both. Fading means that the colour changes and lightens. Bleeding is the transfer of colour to a secondary, accompanying fibre material. This is often expressed as soiling or staining meaning that the accompanying material gets soiled or stained.
Generally fastness properties are expressed in ratings of fastness. Normally they range from rating 5, which means unchanged to rating 1, which means major changes. Only the light fastness ratings range up to eight for the best behaviour. They are mostly evaluated on the so-called blue scales. These contain stripes of standard dyeings on wool with eight blue dyestuffs that have different light fastness. The other fastness ratings are normally evaluated by the grey scales for bleeding and for fading. They consist of five different grey colour gradations and are compared with the tested textile and its prescribed adjacent material.
Colour fastness is assessed generally by comparing any staining of specified adjacent fabrics during the test with a set of standard ‘grey scales’. A numerical grading is given on a scale of 1–5, where 1 is very poor and 5 is excellent. Generally, a grade of 4 or above is deemed acceptable for commercial use.
Material composition affects a great deal for color fastness. By nature, some materials are always better than others when color fastness is concerned.
For instance, the color fastness of Polyester and Nylon fabrics are normally one grade better than Denim’s and Canvas’s. Therefore, the common standard for Denim, Canvas, Print Textiles, Velvet Textiles and Genuine or Suede Leather is set at a relatively lower level, which is only Dry: 3.0 and Wet: 2.0, as people in the industry understand and expect that it is difficult for these materials to achieve a high color fastness standard.
Other factors that affect color fastness include the specific dye used in the dyeing process, the dyeing process itself, any additives, fixatives or softeners used, and the way of washing of the fabrics etc.
•The chemical nature of the fiber. For example, cellulosic fibers dyed with reactive or vat dyes will show good fastness properties. Protein fibers dyed with acid mordant and reactive dyes will achieve good fastness properties and so on. That is to say compatibility of dye with the fiber is very important.
The molecular structure (e.g.) of a dye molecule: If the dye molecule is larger in size, it will be tightly entrapped inside the inter-polymer chain space of a fiber. Thus, the fastness will be better.
The molecular structure (e.g.) of a dye molecule: If the dye molecule is larger in size, it will be tightly entrapped inside the inter-polymer chain space of a fiber. Thus, the fastness will be better.
The manner in which the dye is bonded to the fiber or the physical form present.
The amount of dye present in the fiber i.e. depth of shade. A deep shade will be less fast than a pale or light shade.
The presence of other chemicals in the material.
The actual conditions prevailing during exposure.
Color also affects color fastness. Materials in darker colors tends to have lower color fastness than lighter color materials.Also, due to the chemical properties of the dye, there are a few colors that are now widely known to be more problematic, such as Red, Navy Blue & Black.
The actual conditions prevailing during exposure.
Color also affects color fastness. Materials in darker colors tends to have lower color fastness than lighter color materials.Also, due to the chemical properties of the dye, there are a few colors that are now widely known to be more problematic, such as Red, Navy Blue & Black.
As such, during product development, when these fabrics are involved, it is better to pay special attention to make sure that the material suppliers would handle the fabrics carefully. Otherwise, you might end up with a product that will stain clothes.
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