Leather

Cleaning leather

Even cleaning has the potential to damage leather. For this reason, cleaning should not be considered as an automatic option for leather objects. Cleaning is recommended for:

• objects which need cleaning to prevent deterioration of the leather, which can be caused by surface deposits and/or mould growth; and

• recently-acquired objects. Before their addition to the collection, they should be inspected and cleaned if necessary. This is essential to reduce the risk of contaminating the rest of the collection.

Before cleaning leather objects, consider:

• the type and condition of the surface to be cleaned;

• the nature of any contaminants or dirt;

• the type of leather; and

• exactly what is to be cleaned.

Dirt or other accretions which have accumulated during an object's useful life may be seen as historic evidence of the object's use. You may not want to clean this evidence away.

What to clean

Surface deposits which may need to be removed by cleaning include:

• dirt, dust and salts;

• fatty spews and gummy spews—materials which migrate to the surface from the lubricants used on leather; and

• mould.

To identify crystalline salts, spews and mould you may need to examine the leather surface under magnification:

• the crystalline nature of salts would be clearly evident;

• mould can be identified by the presence of fine, fibrous strands; and

• fatty spews appear greasy, and can be difficult to remove; gummy spews look like resin deposits on the surface of the leather.

Cleaning guidelines

Before cleaning any leather objects, remember to assess the condition of the surface being cleaned. If the object is fragile, cleaning can cause further damage; and it might be better to protect the object from further soiling rather than cleaning it.

It is important to remember that cleaning can stain leather, shift dyes as well as dirt within leather, and remove lubricants from leather. Always make sure that cleaning is necessary before starting.

If cleaning is necessary and the object is able to withstand it, there are a number of techniques you can use.

Vacuum cleaning, with the nozzle just above the leather surface and the power on the lowest setting, is probably the safest cleaning method. It is particularly suited to dusty leather which is in good condition. Place a gauze screen on the end of the nozzle when cleaning. This prevents fragments of leather being lost in the vacuum cleaner. If fragments are being lifted, reduce the suction of the vacuum cleaner.

Brushing with a soft, squirrel hair or camel hair brush is another way of removing surface dirt. Note that even using a soft-bristled brush can damage fragile objects—because dust is abrasive and can scratch a fragile surface. Also, small pieces of damaged leather may be dislodged.

Blowing dirt away with compressed air is appropriate for some objects. Take care that the air stream is not too strong, because it could damage fragile surfaces and dislodge leather fragments. Do this either outside or in a fume cupboard: to prevent dust being redeposited on the object.

Granular erasers can be used to remove more stubborn dirt. Use this method only on surfaces which are in good condition. Remember also that some erasers contain chemicals which can contribute to the deterioration of leather; so it is important that you select your eraser carefully. This is particularly important—it can be difficult to remove all traces of the eraser after cleaning.

To remove thick surface deposits such as those occasionally formed by fatty spews, scrape the surface using a soft, wooden spatula. This method should be used only to remove the bulk of the deposit; and care must be taken not to damage the leather surface. Solvents can be used to remove the remainder of the deposit left after scraping. This method is described below.

Residues or thin films of fatty or gummy spews can be removed using petroleum-based solvents such as white spirit or hexane.

It is necessary to control the application of these solvents, because they can easily spread into the leather and dissolve fats in the body of the skin. The solvents can be applied with a small brush or cotton bud, or a sponge for larger areas. The solvents will soften the fats which you can then remove with a clean, cotton bud or your wooden spatula.

Use a slightly moistened sponge to remove water-soluble dirt from leather objects which are in good condition.

Alcohol or alcohol/water mixtures can be used to remove surface salts. Water can stain and damage leather, so keep the water content low. Test the mixture to make sure that it has no effect on the leather surface.

An emulsion cleaner is very effective for removing stubborn dirt. Because this formulation contains some water, test it in an inconspicuous area before applying it on a large scale.

Straitjacket before cleaning. Photograph courtesy of the Western Australian Museum

Straitjacket after cleaning with emulsion cleaner. Photograph courtesy of the Western Australian Museum

Saddle soap-a note of caution

Anecdotal evidence suggests that, although saddle soap appears to have little detrimental effect on leather objects which are still in use, museum objects which have been cleaned with this soap often seem to be in a worse condition than untreated objects.

Of major concern is the alkaline nature of saddle soaps and the effect that the alkalines can have on leather, which is naturally acidic. If saddle soap is the only available cleaning option, it is important to minimise the amount of moisture used. This reduces the penetration of the soap into the leather and minimises the potentially damaging effects of the soap.