Conservation advice: Cleaning Soot Damaged Objects

Objects conservators at the Australian War Memorial have contributed this information. If you need more information, ring the Conservation Section on (02) 6243 4444 and ask for an objects conservator. Textiles, paintings, and paper (including books and photographs) conservators are also available for consultation regarding their areas of specialization.

Soot

Soot is a mixture of oil, carbon and tar compounds that represent the materials destroyed in a fire. The particle size is so fine that it is able to become lodged in microscopic cracks in the surface of an object and become electrostatically bonded.

Handling

Soot is a corrosive substance and its effects can be made worse if an object is touched with bare hands, the natural oils present in skin causing possible etching of metal surfaces for example. Handle objects as little as possible and wearing soft cotton or latex gloves when handling metals or any precious item is highly recommended. Handling will also result in compacting the soot layer, causing it to adhere more tightly to the surface and be driven further into the object. Ensure gloves are changed as soon as they become dirty to avoid the transfer of soot onto other objects.

Cleaning

Cleaning should be undertaken in three stages: vacuuming, followed by dry surface cleaning, and then wet surface cleaning as a last resort.

Safety is important. Fires can release a number of hazardous materials (such as toxic chemicals and asbestos) which may become deposited on the object as part of the soot. It is important to take safety precautions such as wearing gloves whilst handling objects.

Vacuuming

Vacuuming is most effective if undertaken as soon as possible following a fire and before the object is handled. The vacuum nozzle should not come into direct contact with the object and should be used without any attachments or brushes which would only serve to drive the soot further into the surface.

Dry Surface Cleaning

Erasers such as vinyl erasers, mechanical vinyl erasers and eraser dust are very effective in removing soot from objects. Only white erasers should be used for cleaning objects as others may contain materials such as fine glass particles that would damage the object further. Eraser dust can be easily made at home by using the finest grade on a cheese grater in the kitchen. Always remembering to wear gloves when handling the object, the dust can be gently massaged over the surface and should be changed as it becomes dirty. Document cleaning pads (available from art suppliers) are fabric bags containing very fine eraser dust – these may also be used for cleaning.

Soot sponges are also very useful but more difficult to obtain and are made from vulcanized rubber. Conservation suppliers Zetta Florence sell a Dry Cleaning Sponge, and other brands such as Smoke Sponge, Sootmaster (for cleaning fireplaces) and Gonzo’s Smoke-off Sponge should be available from hardware stores. Groom Stick is a material used by conservators in the removal of soot and is available from conservation suppliers. Microfibre dusting cloths may be used with a gentle lifting motion rather than wiping.

Wet Cleaning

Wet cleaning should only be attempted as a last resort. As soot is water repellent in nature it is necessary to use a detergent in conjunction with water in order to lift and remove the soot. Only a weak solution of a very mild, pure soap in water should be used. Stronger detergent solutions must not be used as this may lead to further damage. Solvents such as white spirits or methylated spirits may be used with extreme care and applied to the object with cotton wool swabs. As the use of water and solvents as cleaning agents may result in loss of colour from certain objects, spot tests should be conducted as the first step in cleaning before attempting the object as a whole.

Cotton swabs can be easily made by tightly rolling cotton wool around the end of a bamboo/wooden skewer. These are preferable to commercially available cotton buds as solvents can dissolve the plastic stalks, redepositing them on the object’s surface.

The swab should be lightly moistened with either a weak solution of warm soapy water or a solvent then gently rolled across the surface of the object. Do not rub or wipe with the swab, as this may ingrain the soot and carbon further into the surface of the object.

It is very important that the object is never fully immersed in water or solvent. Immersion prevents any changes to the object being easily observed and limits control over any reactions taking place. Cleaning should always be undertaken slowly and methodically.

Treating Specific Materials

Wood furniture – wipe surface with cotton rags barely moistened with white spirits then buff with a clean, soft lint-free cloth.
Bronze – clean with solvent then buff dry as with wood furniture.
Metal and glass – clean with water and mild soap. Follow by rinsing with water and then methylated spirits. The methylated spirits will ensure that no moisture remains behind and the object is thoroughly dry. Avoid using water on iron-based metals, use solvents instead.
Ceramics – high fired wares may be treated in a similar manner to glass, but low-fired wares may require specialist treatment.
Smells – following cleaning, small objects can be placed in a zip-lock bag with baking soda, clay cat litter or activated charcoal (such as Odour Eaters) which will absorb the smell over time. Isolate the object from direct contact with the absorbent material with a sheet of paper or plastic.

If a damaged object is valuable or precious, or you have any doubt about cleaning an object yourself it may be worth taking it to a private conservator for assessment and possible treatment. Proceed with caution – treatments carried out at home may cause unintentional damage that even professional conservation treatment may not be able to fully deal with.