Difference between revisions of "Colour fastness - Light fastness of leather"

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==Light fastness of leather==
 
==Light fastness of leather==
The fading of leather is one of the main reasons for [[leather damages|damage to leather]] objects, besides [[leather damages|damages]] caused by perspiration, mechanical stress and aging.
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Fading of leather is one of the main reasons for [[leather damages|damage to leather]] objects, apart from [[leather damages|damages]] caused by sweat and body grease, mechanical stress and aging.
  
The lightfastness of a material describes its resistance to fading by light, in particular by the constant irradiation of UV light. Among the [[types of leather]], especially [[aniline leather|aniline-coloured porous leather]] is at risk of losing the original [[leather colour|hue]]. The less warm and natural [[finish|pigmented leather]] are less endangered.
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The lightfastness of a material describes its resistance to fading by light, in particular by the constant rradiation of UV light. Among the [[types of leather]], especially [[aniline leather|aniline-coloured porous leather]] is at risk of losing the original [[leather colour|hue]]. The more engineered[[finish|pigmented leather]] is less prone to this phenomenon.  
  
  
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<p>&nbsp;</p>
 
<p>&nbsp;</p>
  
The light fastness of leather - as well as in the textile industry - are measured by means of the so-called blue scale. In doing so, eight blue wool strips of descending light fastness are placed together with a sample of the leather to be tested in ultraviolet light. Before, part of the sample surface and a part of the wool strip surface is covered and compared after the exposure. The degrees of light fastness are expressed as follows:
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The light fastness of leather - as well as in the textile industry - are measured by means of the so-called blue scale. In doing so, eight blue wool strips of descending light fastness are placed together with a sample of the leather to be tested in ultraviolet light. A part of the sample surface and a part of the wool strip surface is covered and compared after the exposure. The degrees of light fastness are expressed as follows:
  
  
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For leather, grade 6 is already referred to as light resistant, since it fades faster than textiles. [[Aniline leather]] at least must have grade 3 or 4.
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For leather, grade 6 is already referred to as light resistant, since it fades faster than textiles. [[Aniline leather]] must have a grade of at least 3 or 4.
  
  
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</p>
 
</p>
 
<p align=center>
 
<p align=center>
''The [[Leather quality#Test equipment|xenon-test]] shows the fading sensitivity. The [[Leather grain - Grain side|grain side]] is faded recognizable.''<br></p>
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''The [[Leather quality#Test equipment|xenon-test]] shows the fading sensitivity. The fading on the [[Leather grain - Grain side|grain side]] is easily recognisable.''<br></p>
 
<p>&nbsp;</p>
 
<p>&nbsp;</p>
  
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The following parameters influence the fading sensitivity:
 
The following parameters influence the fading sensitivity:
* The sensitivity to fading is due to the leather, but to the used [[leather colour|dye]].
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* The sensitivity to fading is not due to the leather, but due to the used [[leather colour|dye]].
 
* Not all dyes fade easy. Two different black or red tones can behave completely different. Reliability about the fading sensitivity can be provided by [[leather quality|comparison tests]]. The sensitivity to light influences is checked with the xenon test.
 
* Not all dyes fade easy. Two different black or red tones can behave completely different. Reliability about the fading sensitivity can be provided by [[leather quality|comparison tests]]. The sensitivity to light influences is checked with the xenon test.
 
* The more [[leather colour]] is applied onto leather, the better is the light fastness. Unfortunately, strong colour application affects the [[Haptic evaluation of leather surfaces|haptic]] of leather.
 
* The more [[leather colour]] is applied onto leather, the better is the light fastness. Unfortunately, strong colour application affects the [[Haptic evaluation of leather surfaces|haptic]] of leather.
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==[[Vegetable-tanned leather]]==
 
==[[Vegetable-tanned leather]]==
The [[leather colour|dye]] in [[aniline leather]] or the [[finish|pigment based coatings]] on [[finish|finished]] leather become lighter by light. In the case of uncoloured vegetal tanned leathers, it behaves differently. The leather darkens by light. And the darkness can fade with time. Probably this effect is related to [[Oils & fats in the leather industry|fats and oils]] in the leather.
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The [[leather colour|dye]] in [[aniline leather]] or the [[finish|pigment based coatings]] on [[finish|finished]] leather fade causing the surface to become lighter. In the case of uncoloured vegetable tanned leathers, it behaves differently. The leather darkens by light. And the darkness can fade with time. This effect is probably related to [[Oils & fats in the leather industry|fats and oils]] in the leather.
  
  

Revision as of 22:03, 6 February 2017

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Möbel-Nubuk-verblichen-03-blau.jpg


Light fastness of leather

Fading of leather is one of the main reasons for damage to leather objects, apart from damages caused by sweat and body grease, mechanical stress and aging.

The lightfastness of a material describes its resistance to fading by light, in particular by the constant rradiation of UV light. Among the types of leather, especially aniline-coloured porous leather is at risk of losing the original hue. The more engineeredpigmented leather is less prone to this phenomenon.


Anilinleder-ausbleichen-Tag-00.jpg Anilinleder-ausbleichen-Tag-16.jpg Anilinleder-ausbleichen-Tag-50.jpg

Aniline leather day 0, day 16 and day 50 in sunlight.

 

Sessel-Nubuk-gepraegt-2010-.jpg

Faded, embossed nubuck in comparison to the original pattern.

 

The light fastness of leather - as well as in the textile industry - are measured by means of the so-called blue scale. In doing so, eight blue wool strips of descending light fastness are placed together with a sample of the leather to be tested in ultraviolet light. A part of the sample surface and a part of the wool strip surface is covered and compared after the exposure. The degrees of light fastness are expressed as follows:


Degree designation corresponds in Central Europe
an exposure time of
8 outstanding 700 days
7 excellent 350 days
6 very good 160 days
5 good 80 days
4 pretty good 40 days
3 moderate 20 days
2 low 10 days
1 very low 5 days


For leather, grade 6 is already referred to as light resistant, since it fades faster than textiles. Aniline leather must have a grade of at least 3 or 4.


Xenon test

In the laboratory, there are devices that measure the fading sensitivity. Widely used is the xenon test, which attempts to simulate sunlight.


Xenon-Test-Leder-01.jpg Lichtalterung-01.jpg

Xenon-Test-Leder-02.jpg

The xenon-test shows the fading sensitivity. The fading on the grain side is easily recognisable.

 

Influence variables on fading sensitivity

The following parameters influence the fading sensitivity:

  • The sensitivity to fading is not due to the leather, but due to the used dye.
  • Not all dyes fade easy. Two different black or red tones can behave completely different. Reliability about the fading sensitivity can be provided by comparison tests. The sensitivity to light influences is checked with the xenon test.
  • The more leather colour is applied onto leather, the better is the light fastness. Unfortunately, strong colour application affects the haptic of leather.
  • For leathers dyed in the same shade, the fading sensitivity is lower.
  • UV-protective lacquers improve the fading behaviour of leather.
  • The fading behaviour of suede, nubuck and aniline leather is not different.
  • The fading behaviour of textiles in case of identical dyes is significantly better due to the improved fixability of the dyes in textiles.


Ausbleichen-1311-bis-0302.jpg

Aniline leather covered in the middle after 2.5 months in the window.

 

The following illustrations demonstrate the effects that UV light can have on the appearance of an insufficient protected leather. The examples show aniline, suede and nubuck.


Bleich1.jpg Möbel-Anilin-stark-verblich.jpg

Bleich3.jpg Bleich4.jpg



Vegetable-tanned leather

The dye in aniline leather or the pigment based coatings on finished leather fade causing the surface to become lighter. In the case of uncoloured vegetable tanned leathers, it behaves differently. The leather darkens by light. And the darkness can fade with time. This effect is probably related to fats and oils in the leather.


Naturleder-dunkeln-Tag-00.jpg Naturleder-dunkeln-Tag-16.jpg Naturleder-dunkeln-Tag-50.jpg

Vegetable-tanned leather day 0, day 16 and day 50 in sunlight.

 

Additional information


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