Difference between revisions of "Chrome tanned"

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==History of chrome tanning==
 
==History of chrome tanning==
Until the 19th century, there was little progress in the [[tanning|tanning process]]. While there was some use of [[Tawing with alum|alum (aluminium) salts]] and [[tanning#Tanning methods|other tanning methods]], most tanning was done by the [[vegetable tanning]] process. In 1858, chrome tanning was invented by the German technologist F. Knapp & Cavalin, a Swede. However, it was an American chemist by the name of Augustus Schultz who first patented the chrome tanning process.  
+
Until the 19th century, there was little development in the [[tanning|tanning process]]. While there was some use of [[Tawing with alum|alum (aluminium) salts]] and [[tanning#Tanning methods|other tanning methods]], [[vegetable-tanned leather|vegetable tanning]] was the most prevalent. In 1858, chrome tanning was invented by the German technologist Friedrich Knapp and Hylten Cavalin from Sweden. However, it was an American chemist called Augustus Schultz who first patented the chrome tanning process with alkaline chromium (III) sulfate as [[Tannins|tanning agent]].  
  
In the following decades, chrome tanning became the most common and dominant kind of [[tanning]]. Chrome tanning process meant leathers could be tanned in a matter of days in comparison to vegetable tanning. The reduced time was a main decisive factor to Chrome tanning becoming one of the main tanning process. The discovery of chrome tanning, connected to the process of [[Oils & fats in the leather industry#fatliquoring (regreasing)|fatliquoring (regreasing)]] and the development of [[leather colour|synthetic dyes]] has, enables the variety of currently known appearance of leather. The chromium salts belongs to the group of [[Mineral tanning|mineral tannins]].
+
Chromium(III) occurs naturally in the Earth's crust. It is often found in the form of chromium minerals such as chromite or chromite spinel. The largest deposits of chromite minerals are located in South Africa, Kazakhstan, India, Russia, Turkey, the Philippines, and Zimbabwe. Chromium(III) is extracted from these ores and converted into various compounds to fulfill its different applications.
  
Immediately after tanning, the leather is still wet and gets a blue tinge, hence it is also referred to as [[wet blue]].
 
  
 +
<p align=center>
 +
[[bild:Ball-Chrome-tanning-1920.jpg|500px]]
 +
</p>
 +
<p align=center>
 +
''Beginnings of chrome tanning: Ball of chrome-tanned cow leather from before 1920 ([[Leather museum|© German Ledermuseum, C. Perl-Appl]]).''<br></p>
 +
<p>&nbsp;</p>
  
 +
In the following decades, chrome tanning became the most common and dominant form of [[tanning]]. One of the main reasons why it was adopted so rapidly is that the process was much faster than [[Vegetable-tanned leather|vegetable tanning]]. In addition, the temperature resistance of chrome-tanned leather was an important factor in [[Leather shoes|shoe manufacture]]. The vulcanization of rubber creates heat that chrome-tanned leather tolerates without [[Shrunken leather - leather shrinkage|shrinking]]. With chrome-tanned leather, the rubber soles could be vulcanized (connected) to the [[Leather shoes|upper leather]] of the shoes without having to sew the sole to the upper leather. That was a big cost saving in industrial shoe manufacturing which is still valid today and cannot be achieved by other [[Tanning leather|tanning methods]]. Another benefit of chrome-tanned leather was weight. [[Vegetable-tanned leather|Vegetable-tanned leather]] is stronger and heavier, but lightweight chrome-tanned leather was more popular for [[leather shoes|children's or women's shoes]].
 +
 +
The invention of chrome tanning coincided with the discovery of the [[Oils & fats in the leather industry#fatliquoring (regreasing)|fatliquoring (regreasing)]] process and also the development of [[leather colour|synthetic dyes]]. Together these changes to the chemistry of leather production led to chrome tanning becoming the preferred method. Chromium salts belong to the group of [[Mineral tanning|mineral tannins]].
 +
 +
Immediately after tanning, the leather is still wet and is tinged with blue, hence it is also referred to as [[wet blue]].
 +
 +
 +
<p align=center>
 +
[[bild:ChromIII-01.jpg|500px]]
 +
</p>
 
<p align=center>
 
<p align=center>
[[bild:ChromIII-01.jpg|250px]]
+
[[bild:ChromIII-02.jpg|500px]]
[[bild:ChromIII-02.jpg|250px]]
+
 
</p>
 
</p>
 
<p align=center>
 
<p align=center>
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==The global importance of chrome tanning==
 
==The global importance of chrome tanning==
Chrome tanning with chromium (III) salts accounts for around 85 percent of global [[leather production]] (as per 2014). 95% of [[leather shoes|shoe upper leather]], 70% of [[leather furniture|leather upholstery]] (but decreasing in favour of [[Chrome tanned#Chrome-free leather - FOC = Free of Chrome|FOC-leather) and almost 100% of [[Leather clothing|clothing leather]] are chrome tanned.  
+
Chrome tanning with chromium (III) salts accounts for around 85 percent of global [[leather production]] (as per 2014). 95% of [[leather shoes|shoe upper leather]], 70% of [[leather furniture|leather upholstery]] (but decreasing in favour of [[Chrome tanned#Chrome-free leather - FOC = Free of Chrome|FOC-leather)]] and almost 100% of [[Leather clothing|clothing leather]] are chrome tanned.  
  
Unlike [[Vegetable-tanned leather|vegetable tanned leather]], it has twice the tensile strength, while it has a lighter weight because the chromium salts used for tanning do not fill the skin. The tannin makes up only 4% (with newer leathers even only about 1.5%) of the leather weight, while [[vegetable-tanned leather]] has a tannin content of about 20 percent.
+
Although it has twice the tensile strength of  [[Vegetable-tanned leather|vegetable tanned leather]], chrome-tanned leather weighs less because the skin does not fully absorb the chromium salts used for tanning. The tannin makes up just 4% (with newer leathers only about 1.5%) of the leather weight, while [[vegetable-tanned leather]] has a tannin content of about 20 percent.
  
Chrome-tanned leather is easier to [[Waterproofing leather|hydrophobilize]] as with other tanning alternatives and the leather can easier be [[Haptic evaluation of leather surfaces|softened]]. The [[tanning|tanning process]] is faster and less tanning chemistry is needed compared to [[vegetable-tanned leather]].
+
Chrome-tanned leather is more easily [[Waterproofing leather|hydrophobized]] compared to other tanning alternatives and the leather can be [[Haptic evaluation of leather surfaces|softened]] more easily. The [[tanning|tanning process]] is faster and requires less tanning chemistry than [[vegetable-tanned leather]].
  
 
Cost saving: Freshly tanned [[wet blue]] with its characteristic bluish tint is globally transportable and can be stored well. This facilitates unlimited international sales and global processing.
 
Cost saving: Freshly tanned [[wet blue]] with its characteristic bluish tint is globally transportable and can be stored well. This facilitates unlimited international sales and global processing.
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</p>
 
</p>
 
<p align=center>
 
<p align=center>
[[bild:Gerberei-Gerbfass-04.jpg|250px]]
+
[[bild:Gerberei-Gerbfass-04.jpg|500px]]
[[bild:Wet-Blue-06.jpg|250px]]
+
 
</p>
 
</p>
 
<p align=center>
 
<p align=center>
''Chrom-Gerbung im [[Gerbfass]]''<br></p>
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[[bild:Wet-Blue-06.jpg|500px]]
 +
</p>
 +
<p align=center>
 +
''Chrome tanning in the [[tanning leather#Tanning drum|tanning drum]].''<br></p>
 
<p>&nbsp;</p>
 
<p>&nbsp;</p>
  
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{| class="prettytable right"  
 
{| class="prettytable right"  
|+'''Anteil chromgegerbter Leder in verschiedenen Verwendungsbereichen'''
+
|+'''Proportion of chrome-tanned leather in various sectors of use'''
  
!bgcolor="#cccccc" | Bereich || bgcolor="#cccccc" | Chromgegerbte Leder in % || bgcolor="#cccccc" | Tendenz
+
!bgcolor="#cccccc" | Area || bgcolor="#cccccc" | Chrome-tanned leather in % || bgcolor="#cccccc" | tendency
 
|-  
 
|-  
| [[Lederschuhe#Oberleder|Schuhoberleder]]
+
| [[Leather shoes#Oberleder|Shoe upper leather]]
 
|style="text-align: center"| 95
 
|style="text-align: center"| 95
|style="text-align: center"| Keine Änderung
+
|style="text-align: center"| No change
 
|-
 
|-
| [[Möbelleder]]
+
| [[Leather furniture|Furniture leather]]
 
|style="text-align: center"| 70
 
|style="text-align: center"| 70
|style="text-align: center"| Abnahme zugunsten [[Chromgerbung#FOC = Free of Chrome|FOC]]
+
|style="text-align: center"| Decrease in favour [[Chrome tanned#Chrome-free leather - FOC = Free of Chrome|FOC-leather)]]
 
|-
 
|-
| [[Autoleder]]
+
| [[Car leather]]
 
|style="text-align: center"| 50
 
|style="text-align: center"| 50
|style="text-align: center"| Abnahme zugunsten [[Chromgerbung#FOC = Free of Chrome|FOC]]
+
|style="text-align: center"| Decrease in favour [[Chrome tanned#Chrome-free leather - FOC = Free of Chrome|FOC-leather)]]
 
|-
 
|-
| [[Bekleidungsleder]]
+
| [[Leather clothing|Garment leather]]
 
|style="text-align: center"| 100
 
|style="text-align: center"| 100
|style="text-align: center"| Keine Änderung
+
|style="text-align: center"| No change
 
|-
 
|-
| [[Galanterieleder]]
+
| [[Leather handbags|Bags]], [[leather belt|belts]], [[Leather accessories|accessories]]
 
|style="text-align: center"| 60
 
|style="text-align: center"| 60
|style="text-align: center"| Keine Änderung
+
|style="text-align: center"| No change
 
|-
 
|-
| [[Lederschuhe#Sohlleder Sohlenleder|Sohlleder]]
+
| [[Leather shoes#Sole leather|Sole leather]]
 
|style="text-align: center"| -
 
|style="text-align: center"| -
|style="text-align: center"| Keine Änderung
+
|style="text-align: center"| No change
 
|}
 
|}
  
''Quelle: Zeitschrift Leder & Häute Markt 3/2008, S. 46.''
+
''Source: Journal leather & skins market - Leder & Häute Markt 3/2008, page 46.''
  
  
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</p>
 
</p>
 
<p align=center>
 
<p align=center>
''"[[Wet Blue]]" - feuchtes, grau-bläuliches [[Leder]] direkt nach der Chromgerbung durch Chrom eingefärbt.''<br></p>
+
''"[[Wet blue]]" = damp, grey-bluish leather dyed right after chrome tanning by chromium.''<br></p>
 
<p>&nbsp;</p>
 
<p>&nbsp;</p>
  
Als Gerbstoff wird fast immer 33%iges basisches Chromsulfat mit einem Chrom(III)-Oxid-Gehalt von etwa 26% verwendet. Weltweit werden jährlich 480 000 Tonnen an Chromgerbstoffen produziert, was etwa 125 000 Tonnen Chrom(III)-Oxid entspricht. '''Die Verwendung von Chrom (III)-Salzen (Chromalaun) gilt als gesundheitlich unbedenklich''' und wirft bei den allermeisten Menschen (trotz intensiven Hautkontaktes im Schuh- oder Bekleidungsbereich) keinerlei Schwierigkeiten auf. Trinkwasser darf 50 Mikrogramm (Chrom III) pro Liter enthalten.  
+
The chrome-tanning agent nearly always contains 33% basic chromium sulphate and 26% chromium (III) oxide. Annually 480,000 tonnes are produced in chrome tanning worldwide, which is about 125,000 tonnes of chromium (III) oxide. The use of chromium (III) salts is considered harmless to health and does not cause difficulties in the vast majority of people, despite intensive skin contact in footwear or apparel. Drinking water is allowed to contain 50 micrograms (chromium III) per litre.  
  
Hauptlieferanten für Chrom sind Südafrika mit 38%, Indien mit 20%, Kasachstan mit 15%, Türkei mit 7%, [https://www.youtube.com/watch?v=h8yBK_sLqrE&list=UUE6o00uemdT7FOb2hDoyUsQ Russland], [https://www.youtube.com/watch?v=xSQ_fwiPD0M&list=PLdGEmp0I4BawmOicnQn_MkgYSgFM3bKel Brasilien] und Zimbabwe je mit 3% und Finnland mit 2%.  
+
Major suppliers of chromium are South Africa with 38%, India 20%, Kazakhstan 15%, Turkey with 7%, Russia, Brazil and Zimbabwe each with 3% and Finland with 2%. Chromium III in nature: Earth's atmosphere contains 0.005-300 mg/kg, land plants contain 0.03-20 mg/kg or marine plankton contains 2.2-7.5 mg/kg and human bones 0.1-33 mg/kg. Only about 1% of the world production of chromium III is used for leather production. Steel contains 180-260 g/kg chromium III.
  
  
 
==Chrome-free leather - FOC = Free of Chrome==
 
==Chrome-free leather - FOC = Free of Chrome==
'''FOC''' (engl. free of chrome, chromfrei) bezeichnet mit [[Synthetische Gerbung|synthetischen Stoffen]] oder [[Pflanzlich gegerbtes Leder|pflanzlichen Mitteln]] ohne Verwendung von Chrom gegerbtes Leder. Sie sind heute zunehmend bei Polsterledern im [[Autoleder|Fahrzeug-]] und [[Möbelleder|Möbelbereich]] anzutreffen.
+
FOC (free of chrome, chrome-free) labelled leather is [[tanning|tanned]] with [[tannins]] that do  not contain chromium (III). They are now increasingly used in [[car leather|automotive upholstery]] and [[leather furniture|furniture upholstery]]. The [[car leather|leather seats of Audi and Porsche]] are always free of chrome.  
  
Die [[Autoleder]] von Audi, Porsche und Volkswagen sind z. B. grundsätzlich chromfrei.
+
The production of FOC-leather is more complex than that of the chrome-tanned leather. For example, in the [[tanning|tanning process]], an exact temperature must be reached to tan successfully. FOC leather is mostly produced in developed countries.  
  
Die Herstellung von FOC-Ledern ist aufwändiger als die der chromgegerbten Leder. Es muss z. B. im Gerbprozess auf die exakte Einhaltung der Temperaturen geachtet werden. Daher werden FOC-Leder eher in den entwickelten Ländern produziert. Eine Übersicht über die Verteilung der Gerbarten finden Sie unter "[[Gerbung#Gerbarten|Gerbung]]".
+
Frequently chromium-free leather is advertised with descriptions such as "without chromium and pollutants" or "heavy metal-free". This can give the impression that chrome tanning is harmful (heavy metal contamination), whereas tanning with chromium III is absolutely harmless. Many people associate "chrome" with toxic or may have read in the press about the transgressions involving content of  [[Chrome VI - Chromium VI|chromium VI]]. Marketing campaigns for FOC leather usually exaggerate these fears.
  
 +
FOM (free of metal) is the name for leather that has been tanned completely without the use of metals and their compounds (such as aluminium, iron or titanium).
  
<p align=center>
+
Currently, chromium tanning is extremely dominant.  Alternative [[tanning|tanning methods]] are unable to replace it, mainly due to costs and technical considerations. Many [[vegetable-tanned leather|vegetable tanning agents]] occur naturally but they are not readily available in sufficient enough quantities yearly to satisfy the demand for  [[leather industry|leather production worldwide]].
[[bild:Chrom-frei-001.jpg|250px]]
+
</p>
+
<p align=center>
+
''Werbung für chromfreies [[Nubukleder]]''<br></p>
+
<p>&nbsp;</p>
+
  
Häufig wird chromfreies Leder mit Beschreibungen wie "ohne Chrom und Schadstoffe" beworben. Dabei entsteht der Eindruck, das die Chromgerbung mit Schadstoffen belastet sei. So ist es aber nicht. Die Gerbung mit Chrom III ist absolut unbedenklich. Viele Menschen assoziieren mit "Chrom" eine Giftigkeit oder haben in der Presse über Grenzwertüberschreitungen beim [[Chrom-VI|Chrom VI]] gehört. Diese Ängste werden dann beim Marketing genutzt und Alternativen werden angepriesen.  
+
Chrome-free [[tanning]] is being further developed worldwide and the proportion of chrome-free leather is constantly increasing, but the dominance of chrome tanning is still unbroken.
  
'''FOM''' (free of metal) ist die Bezeichnung für Leder, die vollständig ohne Verwendung von Metallen und ihren Verbindungen (etwa Aluminium, Eisen oder Titan) gegerbt worden sind.
 
  
Aktuell ist die ungefährliche Chrom-III-Gerbung dominant und die alternativen [[Gerbung|Gerbarten]] könnten diese Gerbart weder kostenneutral, noch technisch ersetzen. Viele [[Pflanzlich gegerbtes Leder|pflanzliche Gerbstoffe]] haben kein ausreichendes Aufkommen, um den Bedarf an Gerbstoffen für die [[Lederindustrie|Weltproduktion]] an Leder zu befriedigen.  
+
==[[Chrome VI - Chromium VI]]==
 +
[[Chrome VI - Chromium VI|Chromium (VI)]] is harmful and can occur in the leather as a result of improper tanning conditions. However, following thorough research, this can be avoided.
  
 +
* [[Chrome VI - Chromium VI|For more information about chromium VI]]
  
==[[Chrom-VI]]==
 
  
'''Gesundheitsschädlich ist aber [[Chrom-VI|Chrom (VI)]]''', das unter unsachgemäßen Gerbbedingungen im Leder entstehen kann, die aber inzwischen erforscht sind und vermieden werden können.  
+
==Chrome tanning - Ecology==
 +
Environmental considerations with respect to chrome tanning are also important. The chromium-containing [[Wastewater from tanneries|waste water]] and waste materials must be recycled to recover valuable materials. Modern tanneries manage to bind up to 97% of the chromium used in the leather fibre, to keep the waste water load low and to save costs.
  
Fette mit hohen Anteilen ungesättigter Fettsäuren fördern demnach die Bildung von gesundheitsschädlichem Chrom (VI) bei der Chromgerbung. Es wurde bisher auch vermutet, dass ein hoher Anteil an löslichem Chrom (III) zur Oxidation von Chrom (III) zu Chrom (VI) z. B. bei der Verwendung von alkalischen Klebern (Heat-Setting) führen kann. Dieses lässt sich aber nicht reproduzieren. Daher bleibt der beste Schutz vor Chrom (VI) der Einsatz geeigneter Fettungsmittel und die Durchführung der [[pflanzlich gegerbtes Leder|vegetabilen Nachgerbung]] mit [[Quebracho]], Kastanie, [[Mimosa]] oder Tara.
+
Correct disposal of chrome-tanned leathers is crucial. For example, [[car leather|leather seats]] in scrapped cars require appropriate handling because combustion of chrome-tanned leather can produce harmful [[Chrome VI - Chromium VI|chromium (VI)]]. Formation behaviour of chromium (VI) under conditions of high heat (bright sunlight on black [[car leather|car upholstery]] or [[Leather dashboard|dashboard leather]]) should also be reviewed regularly.
  
* [[Chrom-VI|Weitere Informationen zu Chrom VI]]
+
Proponents of [[Vegetable-tanned leather|vegetable tanning]] argue that vegetable tanning agents are natural and chrome tanning agents are not, and also subtly or directly state that "chromium" is a toxic substance, which is not true of chromium(III). Conversely, it is argued that vegetable tanning agents use up natural resources and accelerate deforestation. However, it must be mentioned that in the 1950s twice as much vegetable tanning material was used by the [[tannery|tanneries]] because the demand for vegetable tanned leather was higher at the time.
  
 
+
In several comparisons between chrome tanning, [[Vegetable-tanned leather|vegetable tanning]] and [[Synthetic tanned|synthetic tanning]], there were no relevant advantages of chrome-free tanning. All [[tanning|types of tanning]] are harmless for the workers in a [[tannery]] if they are carried out carefully, the waste materials can be disposed of without any problems and the [[leather waste]] from [[leather production]], the [[leather cutting waste]] from the leather processing companies and the disposal of leather objects after use are not hazardous waste materials.
==Chromgerbung - Ökologie==
+
Auch Umweltüberlegungen sind bezüglich der Chromgerbung relevant. So entstehen etwa bei der Gerbung chromhaltige Abwässer und Reststoffe, die aufbereitet bzw. recycled werden müssen, um wertvolle Stoffe wiederzugewinnen. Moderne Gerbereien schaffen es, bis zu 97% des verwendeten Chroms an die Lederfaser zu binden, um die Abwasserbelastung gering zu halten und Kosten zu sparen.
+
 
+
Auch bei der Entsorgung von chromgegerbten Ledern - etwa bei Sitzen in ausgemusterten Autos - ist eine korrekte Handhabung wichtig, da bei Verbrennung chromgegerbten Leders das schädliche Chrom (VI) erzeugt wird. Überprüft werden muss auch regelmäßig das Verhalten von vorgeschrumpften Ledern auf Armaturenbretten ([[Dashboard-Leder]]) hinsichtlich des Entstehungsverhaltens von Chrom (VI) unter Bedingungen hoher Hitzeeinwirkung (etwa bei starker Sonneneinstrahlung auf schwarzes Leder).
+
 
+
 
+
<werbebanner />
+
  
  
 
== Additional information ==
 
== Additional information ==
 +
* [[Leather production]]
 +
* [[Leather chemistry]]
 +
* [[Wet blue]]
 
* [[Chrome VI - Chromium VI]]
 
* [[Chrome VI - Chromium VI]]
 
<br>
 
<br>
 +
* [[Tannins]]
 
* [[Vegetable-tanned leather]]
 
* [[Vegetable-tanned leather]]
 
* [[Mineral tanning]]
 
* [[Mineral tanning]]
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* [[Brain tanning]]
 
* [[Brain tanning]]
 
<br>
 
<br>
* [[Tannins]]
 
 
* [[Bio leather]]
 
* [[Bio leather]]
* [[Leather production]]
+
 
  
  
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<p align=center>
 
<p align=center>
<flashow>http://www.youtube.com/v/zbj1QicTdpI&fs=1&color1=0x660000&color2=0x550000&border=1|width=500|height=281,25</flashow><br></p>
+
<flashow>//www.youtube.com/v/-qn5R8dKcss&fs=1&color1=0x660000&color2=0x550000&border=1|width=500|height=281,25</flashow><br></p>
 
<p align=center>
 
<p align=center>
 
''The [[leather production]] in a modern [[tannery]].''
 
''The [[leather production]] in a modern [[tannery]].''
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! bgcolor=#eeeeee | [[Tanning leather|Tanning]] methods
 
! bgcolor=#eeeeee | [[Tanning leather|Tanning]] methods
 
|-
 
|-
| bgcolor=#ffffff align=center | [[Chrome tanned|Chrome tanning]] - [[Vegetable-tanned leather]] - [[Chamois leather|Tawing with alum]] - [[Buckskin]] - [[Synthetic tanned|Synthetic tanning]]
+
| bgcolor=#ffffff align=center | [[Chrome tanned|Chrome tanning]] - [[Vegetable-tanned leather]] - [[Synthetic tanned|Synthetic tanning]] - [[Tanning with fats and oils]]
 
|}
 
|}
 
</center>
 
</center>

Latest revision as of 13:59, 20 June 2023

LEATHER-DICTIONARY.jpg


History of chrome tanning

Until the 19th century, there was little development in the tanning process. While there was some use of alum (aluminium) salts and other tanning methods, vegetable tanning was the most prevalent. In 1858, chrome tanning was invented by the German technologist Friedrich Knapp and Hylten Cavalin from Sweden. However, it was an American chemist called Augustus Schultz who first patented the chrome tanning process with alkaline chromium (III) sulfate as tanning agent.

Chromium(III) occurs naturally in the Earth's crust. It is often found in the form of chromium minerals such as chromite or chromite spinel. The largest deposits of chromite minerals are located in South Africa, Kazakhstan, India, Russia, Turkey, the Philippines, and Zimbabwe. Chromium(III) is extracted from these ores and converted into various compounds to fulfill its different applications.


Ball-Chrome-tanning-1920.jpg

Beginnings of chrome tanning: Ball of chrome-tanned cow leather from before 1920 (© German Ledermuseum, C. Perl-Appl).

 

In the following decades, chrome tanning became the most common and dominant form of tanning. One of the main reasons why it was adopted so rapidly is that the process was much faster than vegetable tanning. In addition, the temperature resistance of chrome-tanned leather was an important factor in shoe manufacture. The vulcanization of rubber creates heat that chrome-tanned leather tolerates without shrinking. With chrome-tanned leather, the rubber soles could be vulcanized (connected) to the upper leather of the shoes without having to sew the sole to the upper leather. That was a big cost saving in industrial shoe manufacturing which is still valid today and cannot be achieved by other tanning methods. Another benefit of chrome-tanned leather was weight. Vegetable-tanned leather is stronger and heavier, but lightweight chrome-tanned leather was more popular for children's or women's shoes.

The invention of chrome tanning coincided with the discovery of the fatliquoring (regreasing) process and also the development of synthetic dyes. Together these changes to the chemistry of leather production led to chrome tanning becoming the preferred method. Chromium salts belong to the group of mineral tannins.

Immediately after tanning, the leather is still wet and is tinged with blue, hence it is also referred to as wet blue.


ChromIII-01.jpg

ChromIII-02.jpg

Chromium (III) oxide in powder form.

 

The global importance of chrome tanning

Chrome tanning with chromium (III) salts accounts for around 85 percent of global leather production (as per 2014). 95% of shoe upper leather, 70% of leather upholstery (but decreasing in favour of FOC-leather) and almost 100% of clothing leather are chrome tanned.

Although it has twice the tensile strength of vegetable tanned leather, chrome-tanned leather weighs less because the skin does not fully absorb the chromium salts used for tanning. The tannin makes up just 4% (with newer leathers only about 1.5%) of the leather weight, while vegetable-tanned leather has a tannin content of about 20 percent.

Chrome-tanned leather is more easily hydrophobized compared to other tanning alternatives and the leather can be softened more easily. The tanning process is faster and requires less tanning chemistry than vegetable-tanned leather.

Cost saving: Freshly tanned wet blue with its characteristic bluish tint is globally transportable and can be stored well. This facilitates unlimited international sales and global processing.


ChromIII-03.jpg

Gerberei-Gerbfass-04.jpg

Wet-Blue-06.jpg

Chrome tanning in the tanning drum.

 

Proportion of chrome-tanned leather in various sectors of use
Area Chrome-tanned leather in % tendency
Shoe upper leather 95 No change
Furniture leather 70 Decrease in favour FOC-leather)
Car leather 50 Decrease in favour FOC-leather)
Garment leather 100 No change
Bags, belts, accessories 60 No change
Sole leather - No change

Source: Journal leather & skins market - Leder & Häute Markt 3/2008, page 46.


Wet-blue.jpg Wetblue.jpg

"Wet blue" = damp, grey-bluish leather dyed right after chrome tanning by chromium.

 

The chrome-tanning agent nearly always contains 33% basic chromium sulphate and 26% chromium (III) oxide. Annually 480,000 tonnes are produced in chrome tanning worldwide, which is about 125,000 tonnes of chromium (III) oxide. The use of chromium (III) salts is considered harmless to health and does not cause difficulties in the vast majority of people, despite intensive skin contact in footwear or apparel. Drinking water is allowed to contain 50 micrograms (chromium III) per litre.

Major suppliers of chromium are South Africa with 38%, India 20%, Kazakhstan 15%, Turkey with 7%, Russia, Brazil and Zimbabwe each with 3% and Finland with 2%. Chromium III in nature: Earth's atmosphere contains 0.005-300 mg/kg, land plants contain 0.03-20 mg/kg or marine plankton contains 2.2-7.5 mg/kg and human bones 0.1-33 mg/kg. Only about 1% of the world production of chromium III is used for leather production. Steel contains 180-260 g/kg chromium III.


Chrome-free leather - FOC = Free of Chrome

FOC (free of chrome, chrome-free) labelled leather is tanned with tannins that do not contain chromium (III). They are now increasingly used in automotive upholstery and furniture upholstery. The leather seats of Audi and Porsche are always free of chrome.

The production of FOC-leather is more complex than that of the chrome-tanned leather. For example, in the tanning process, an exact temperature must be reached to tan successfully. FOC leather is mostly produced in developed countries.

Frequently chromium-free leather is advertised with descriptions such as "without chromium and pollutants" or "heavy metal-free". This can give the impression that chrome tanning is harmful (heavy metal contamination), whereas tanning with chromium III is absolutely harmless. Many people associate "chrome" with toxic or may have read in the press about the transgressions involving content of chromium VI. Marketing campaigns for FOC leather usually exaggerate these fears.

FOM (free of metal) is the name for leather that has been tanned completely without the use of metals and their compounds (such as aluminium, iron or titanium).

Currently, chromium tanning is extremely dominant. Alternative tanning methods are unable to replace it, mainly due to costs and technical considerations. Many vegetable tanning agents occur naturally but they are not readily available in sufficient enough quantities yearly to satisfy the demand for leather production worldwide.

Chrome-free tanning is being further developed worldwide and the proportion of chrome-free leather is constantly increasing, but the dominance of chrome tanning is still unbroken.


Chrome VI - Chromium VI

Chromium (VI) is harmful and can occur in the leather as a result of improper tanning conditions. However, following thorough research, this can be avoided.


Chrome tanning - Ecology

Environmental considerations with respect to chrome tanning are also important. The chromium-containing waste water and waste materials must be recycled to recover valuable materials. Modern tanneries manage to bind up to 97% of the chromium used in the leather fibre, to keep the waste water load low and to save costs.

Correct disposal of chrome-tanned leathers is crucial. For example, leather seats in scrapped cars require appropriate handling because combustion of chrome-tanned leather can produce harmful chromium (VI). Formation behaviour of chromium (VI) under conditions of high heat (bright sunlight on black car upholstery or dashboard leather) should also be reviewed regularly.

Proponents of vegetable tanning argue that vegetable tanning agents are natural and chrome tanning agents are not, and also subtly or directly state that "chromium" is a toxic substance, which is not true of chromium(III). Conversely, it is argued that vegetable tanning agents use up natural resources and accelerate deforestation. However, it must be mentioned that in the 1950s twice as much vegetable tanning material was used by the tanneries because the demand for vegetable tanned leather was higher at the time.

In several comparisons between chrome tanning, vegetable tanning and synthetic tanning, there were no relevant advantages of chrome-free tanning. All types of tanning are harmless for the workers in a tannery if they are carried out carefully, the waste materials can be disposed of without any problems and the leather waste from leather production, the leather cutting waste from the leather processing companies and the disposal of leather objects after use are not hazardous waste materials.


Additional information




Video about leather production


The leather production in a modern tannery.


Tanning methods
Chrome tanning - Vegetable-tanned leather - Synthetic tanning - Tanning with fats and oils


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