What is that white stuff on the leather surface?
A surface power, coating or discolouration is usually caused by either:
Fatty spew or (also called fatty bloom)
Mould or Mildew
Salt Efflorescence
This refers to the migration of fats/oils from within the leather that crystallize on the surface when they meet the air. The crystals form on the surface as a white powder or as a 'bloom'.
Fatty spews can look powdery or gummy in appearance and sometimes they have even been described as feathery or fibrous. They don't tend to have a significant odour. In our experience, the origin of the fats/oils that have migrated to the leather surface is either
(i) from an insufficient level of degreasing of the raw material or
(ii) from an issue with the softening / lubricating agents or process stage used when making the leather.
The presence of the bloom is generally more prominent where the leather surface is exposed to air and where the leather is folded over in finished goods. Environmental factors also play a part in the formation of fatty spews (for example temperature and humidity). However, even in ideal conditions, if there is an issue with fat/oil migration in the leather, a fatty spew will likely result at some stage.
There are a number of way to avoid the issue when initially making the leather. There are also methods to remove the fatty spews (and prevent their reoccurrence) in finished goods. Feel free to contact us if you need some advice.
Both Mould and mildew are fungi that generally develop as a result of excessive, unchecked moisture in confined spaces. This results in a coating or discolouration on the leather surface.
Both mould and mildew grow in a wide range of temperatures and humidities. Furthermore, they can eventually damage the leather if the issue remains unresolved. It should be noted that there are specific differences between mould and mildew:
Moulds tend to have a higher profile (extending above the leather surface) and can have a fuzzy appearance. Moulds are generally either dark green, dark red or black in colour and the colour does not significantly change over time. Mildew usually has a flat surface profile (i.e. does not extend upward from the leather surface) and is powdery. It is initially white, grey or mid brown in colour and the colour or depth of shade can change over time.
Mould and mildew require specific conditions to facilitate their growth, not least the presence of mould spores (that act as a type of seed). Like other fungi, the spores require food, water and oxygen to facilitate growth. Increasing (or decreasing) any of these factors will cause mould and mildew to grow (or die). Moisture is the primary cause behind the growth of mould and mildew.
Whilst it is incredibly difficult to prevent mould spores coming into contact with leather, it is possible to create an environment where mould and mildew will not grow i.e. by keeping moisture levels low, ensuring the leather surface remains clean and that the immediate environment is well ventilated. Most leathers will have received a chemical treatment (during their manufacture) that prevents the formation of mould and mildew, but their effect can reduce over time. There are a number of ways to remove mould / mildew in finished leather goods. Feel free to contact us if you need some advice.
In chemistry, efflorescence (which means "to flower out" in French) is the migration of a salt to the surface of a porous material. In leather, this results in a white powder (often “ingrained”) on the surface.
Salt efflorescence is very much less common as a cause of surface discolouration in leathers. Nevertheless, we have on occasions witnessed the effect of salt migration.
It is well understood that salt is a white crystalline substance that gives seawater its characteristic taste and is used for seasoning or preserving food, (i.e. sodium chloride). Nevertheless, in chemistry a salt is defined as any chemical compound formed from the reaction of an acid with a base, with all or part of the hydrogen of the acid replaced by a metal or other cation, e.g. potassium chloride, potassium iodide and calcium chloride. So whilst the salt causing the efflorescence is likely to be sodium chloride, it may be an alternative (i.e. chemically different) salt.
Any salt in leather usually has its origins from either leather processing (i.e. manufacturing) or from contact with perspiring human skin (clearly the latter can only happen if the leather has been worn in a garment of some kind, a glove or some form of footwear). In our experience, the former is rare. Nevertheless, with big brands, consumer and legislative pressures on reducing water usage (during leather manufacture), a consequence of perpetual water re-use and recycling can result in the build up of salts (especially sodium chloride) within the process water. This in term can result in unusually high levels of salt being present in the leather. There are a number of ways to remove a salt efflorescence in finished leather goods (and ensure it does not reoccur). Feel free to contact us if you need some advice.
The "white stuff" on the leather surface in a recent project was identified as salt efflorescence, a relatively rare occurrence with leather in comparison to fatty spews, mould or mildew occurrences...
We developed a methodology to remove the salt and resolve the problem...
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