Definitions Standards

31 October 2008

It is accepted in the leather industry that there are three basic types of leather finishes: aniline, semi-aniline and pigmented finished. But what is the difference between these leather types? If you ask the manufacturers or the users of leather, invariably you will get the same answer for aniline and pigmented finishes from all of them, but almost certainly there will be some confusion over what semi-aniline really is.

Internationally, there are many documents that provide us with definitions of leather terms. Probably the most commonly referred to are the British Standard BS 2780:1983 Glossary of Leather Terms1 and the International Council of Tanners (ICT) International Glossary of Leather Terms2. The definitions of the three finish types given in each document are compared in Table 1. Essentially, the two definitions for aniline leather concur in that both indicate that it should not have any pigment in the finish; if there is a finish present, it should only be coloured with dye. Likewise, the two definitions for pigmented leather state that the finish contains pigment. But there are definitely some differences in interpretation when it comes to semi-aniline. Let's look at the British Standard definition in a bit more detail. It clearly states that a semi-aniline leather can have pigment in the base coat, and in the top coat as well. So therefore, it obviously also meets the criteria for the definition of a pigmented leather. In other words, according to the BS 2780, the only difference between a pigmented leather and a semi-aniline leather is that the base coat should be of a different colour from the top coat; the amount of pigment and the thickness of the finish film may be as much as is required. So, when we look at the European standards for leather, eg the specification for upholstery leather (EN13336)3, why does it give different requirements for the three leather types and why are the requirements for semi-aniline less stringent than they are for pigmented? For example, in EN 13336 pigmented leather is required to pass 250 wet rubs, whereas semi-aniline requires 80 wet rubs to pass. Clearly, these specifications work on the premise that semi-aniline would have a lower performance level than pigmented leather. But, if it is technically possible to produce pigmented leather and call it semi-aniline because it has a contrasting top coat, why should it only perform half as well? (Note: EN13336 applies the terms and definitions given in the ICT International Glossary of Leather Terms - second edition.) Let's look at what the word ‘semi-aniline' itself really means. According to the Chambers Dictionary4 the word Semi- means ‘..denoting half; (loosely) nearly, partly, incompletely...'.  In other words, semi-aniline means that it is nearly but not completely aniline. The definition given by the ICT glossary ‘..incorporating a small quantity of pigment, not so much as to conceal the natural characteristics of the hide' certainly  fits the meaning of the word better than the British Standard definition. A truer meaning for the British Standard description of semi-aniline would be ‘false-aniline'. Why are we so concerned over what these definitions mean? Well, firstly there is the issue of testing. The European standards for leather provide us with requirements that reflect the different performance levels expected from the three different categories of finish type. Having some degree of variation in the definition of one of these categories makes it very difficult for test houses to correctly categorise semi-aniline leather and test it appropriately. This can lead to misleading results and possible false declarations. For example, if leather is deemed to be semi-aniline because it has a pigmented finish with a contrasting top coat it might pass the semi-aniline performance requirement with flying colours. But had it not had a contrasting top coat it would have been tested as pigmented leather and might have failed. We should not expect the colour of the top coat to necessarily affect its level of performance. Now, had it received less pigmented finish on the surface than a pigmented finished leather we would not expect it to perform as well. There is also the issue of price. It is generally expected that aniline leather will cost more than pigmented finished leather because hides and skins that have a good enough grain quality for aniline production are in short supply. Pigmented finishes can cover a multitude of sins and therefore enables better utilisation of the more plentiful lower quality hides and skins. The finish on a semi-aniline leather as described using the ICT definition will only be able to cover minor defects, so a reasonably good quality hide is needed. Therefore, leather buyers expect to pay a higher price for semi-aniline leather than they would pigmented finished. But why should they pay more if the finish has just as much defect-concealing pigment as a pigmented finished leather? The difficulty with such definitions is that they are created by committee and take such a long time to ratify. Technology is fast moving and the official definitions need to be able to keep up. Should we learn to live with such anomalies, or should we decide which definition of semi-aniline is the correct one and remove/re-write the other? Or perhaps we should remove the definition of semi-aniline all together and just have two leather types - aniline with no pigment at all, or pigmented. Certainly it's time we finished it off for good - one way or the other! References 1. British Standard BS 2780, Glossary of Leather Terms, 1983 2. International Glossary of Leather Terms (2nd edition), International Council of Tanners, 1997 3. EN13336, European Committee for Standardisation, Leather - Upholstery leather characteristics - Guide for the selection of leather for furniture, 2004 4. The Chambers Dictionary 10th Edition, 2006. Additional tables and images can be found in the August/ September edition of Leather International

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