Difference between revisions of "Colour fastness - Light fastness of leather"
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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. | 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. | ||
| − | 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- | + | 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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<p> </p> | <p> </p> | ||
| − | The light | + | 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 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. | ||
* For leathers [[leather colour#Dyed leather|dyed in the same shade]], the fading sensitivity is lower. | * For leathers [[leather colour#Dyed leather|dyed in the same shade]], the fading sensitivity is lower. | ||
| − | * UV-protective lacquers improve the fading | + | * UV-protective lacquers improve the fading behaviour of leather. |
| − | * The fading | + | * The fading behaviour of [[suede]], [[nubuck]] and [[aniline leather]] is not different. |
| − | * The fading | + | * The fading behaviour of textiles in case of identical dyes is significantly better due to the improved fixability of the dyes in textiles. |
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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 | + | 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. |
Revision as of 13:10, 31 January 2017
Contents
Light fastness of leather
The fading of leather is one of the main reasons for damage to leather objects, besides damages caused by perspiration, 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-coloured porous leather is at risk of losing the original hue. The less warm and natural pigmented leather are less endangered.
Aniline leather day 0, day 16 and day 50 in sunlight.
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. 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:
| 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 at least must have grade 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.
The xenon-test shows the fading sensitivity. The grain side is faded recognizable.
Influence variables on fading sensitivity
The following parameters influence the fading sensitivity:
- The sensitivity to fading is due to the leather, but 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.
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.
Vegetable-tanned leather
The dye in aniline leather or the pigment based coatings on 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 fats and oils in the leather.
Vegetable-tanned leather day 0, day 16 and day 50 in sunlight.
Additional information
a kotori web solution