Leather

The term leather covers hides or skins which have been processed and preserved by a tannage, which, generally, is either with vegetable tans or chromium salts.
The leather may be in the form of wet chrome tanned material, or dried leather without a surface finish and requiring further finishing treatment (crust or rough leather) or leather with a surface finish requiring no further processing (finished leather). Then there are articles made of leather – gloves, footwear, bags, cases, etc.

Mould growth on leather Generally, leather will contain a fungicide to protect against mould growth, however under adverse storage conditions and inadequate fungicidal protection mould may develop on the leather. Mould growth is favoured by the leather being made wet or by humid conditions ( a relative humidity greater than 70%) and warmth. Temperature changes moisture content and humidity. Leather at 20°C and normal humidity, 65% RH, will contain 14% moisture. If packed in polythene or sealed containers and the temperature rises to say 40°C, moisture is given off, can condense on the sides of the polythene or container and drip back on the leather giving localised high humidity/moisture sufficient to cause mould. Desiccants in such packages are only effective if the leather is well dried before packing. If temperatures can be maintained within reasonable limits, -10°C to + 10°C, then such problems should not arise. Moulds live on the water soluble component of vegetable tans, sugars and grease present in the leather. Because of this, vegetable tanned leathers are more susceptible to mould growth than chrome tanned leathers, as are also leathers with a high grease content.
The physical properties of leather, such as tear strength, are usually unaffected by mould growth unless it is heavy and prolonged. Mould can be cleaned from the leather surface which may appear undamaged.
Alternatively the surface can be frequently permanently discoloured by mould, and where the leather is to received further processing, such as dyeing and finishing, mould growth can give rise to subsequent faults such as irregular dyeing and finishing, or a fatty acid spue due to degradation of the fats. Mould will also grow on articles made from leather if the storage conditions are adverse. Gloves should be packed in dry waterproof containers to prevent water contamination as with other leather articles such as bags, cases etc.

Leather Shoes Leather will absorb or lose moisture to the atmosphere depending on the relative humidity of the atmosphere. Shoes which have been packed in apparent good order and condition may be delivered at the destination with mould damage. Such damage may be caused either by an excess of moisture in the leather during the manufacture of the shoes or holding under damp conditions before packing for export. In some instances mould may be confined to the leather soles of the shoes, either on the inside or outside or both. Another cause of mould growth may be the high moisture content of the packing material, e.g. paper or cork. The natural moisture content of the leather, or cork or wooden components of the shoe, may cause the rusting of buckled and other metal trim, and care is necessary in attributing a cause in this connection. The adequate lacquering of metallic components reduces the likelihood of such problems.

Wet Chrome Tanned Leather Whole hides or skins or splits are packed in the wet condition. Generally they contain fungicide to protect against mould growth and are enclosed by an impervious covering to prevent drying out. Damage to the covering, burst bales etc., will allow the leather to dry out and to lose weight. Whilst some drying can be overcome, thoroughly dried out ‘wet blue’ is unlikely to give a satisfactory finished leather.

Raw Material Raw hides and skins if allowed to become damp will deteriorate due to bacterial action. Wet salted material if contaminated by water will also deteriorate. Occasionally they are subjected to infestation by beetles. Dusting with insecticide is a desirable precaution ensuring the insecticide meets the approval of the country of destination. For all leather and hides, adequate treatment against mould, and possible insects, is desirable. Goods should then be suitably packed mainly to prevent wetting, or drying out in the case of ‘wet blue’. Storage in transport should be such that the original packing remains integral and not so designed as to impair its protective function.