CCI Notes 7/1
Care and Cleaning of Unfinished Wood
Caution! This Note discusses actions that will physically affect the object, and/or procedures that involve the use of chemicals. Exercise caution, and seek qualified assistance if in doubt.
Cleaning bare wood surfaces is complicated by several factors. First, wood is relatively soft and can be damaged by some cleaning techniques. Second, wood degrades with time and use, so older wood surfaces may be even softer than new ones. Finally, wood surfaces may include natural deterioration products and traces of substances that were applied or came in contact with the surface when the item was in use (these are collectively known as 'patina').
Before attempting to clean a wood surface for purposes of conservation, it is important to differentiate between dirt (which is 'bad' and should be removed) and patina (which is 'good' and should be retained). Learning to distinguish between dirt and patina, and knowing where one stops and the other begins, is not easy. However, the more recent dirt from handling and storage in inadequate conditions is generally easier to remove than the patina.
Choosing a cleaning technique should begin with two questions:
- Does cleaning truly need to be done?
- If so, how far should it go?
Having established how much cleaning is necessary, begin with the least aggressive method and move up the scale only if necessary.
The following techniques (in order of aggressiveness) are recommended for cleaning bare wood:
- soft brush and vacuum cleaner
- stiff brush
- eraser powder
- adhesive rubber
- gum eraser
- damp swab
Soft brush and vacuum cleaner
Most objects with firm stable surfaces can be safely cleaned with a soft paintbrush and vacuum cleaner. Brush the dust from the surface into a vacuum cleaner nozzle that is covered with cheesecloth held in place with a rubber band (this will prevent small pieces being accidentally sucked up). A speed controller is useful for regulating suction, provided one can be used with the motor with which the vacuum cleaner is equipped. If an object shows any indication of loose pieces, powdery surface coatings, or delicate components, consider carefully whether or not cleaning is safe. It may be possible to use a soft brush on such items, but do not use a vacuum cleaner.
If the surface is in good condition, a stiff bristle brush may be used to remove ingrained dirt. A round artist's brush with a diameter of about 1 cm is ideal. This type of brush can be used as supplied, or the bristles can be trimmed to increase their effectiveness (as the bristles get shorter they are less flexible and therefore more abrasive). When cleaning with a stiff bristle brush it is important to proceed cautiously. Wood is relatively soft and the top layers of cells, particularly in degraded wood, can be easily damaged. Injudicious cleaning might exaggerate the grain pattern by selectively wearing away the softer early growth. In furniture collections this effect is most often seen in unfinished softwood pieces, such as dry sinks and rustic furnishings.
Draftsman's eraser powders (e.g. Skum-X or Opaline) can be used to remove ingrained dirt from relatively sound surfaces but are not safe for surfaces that have cracks or unevenness where the powder could get left behind. Various kinds of rubber powder are available, but the natural rubber ones are probably best. Rub the powder into the surface with the fingertips until cleaning is seen to be effective. When finished, use a brush to sweep all the crumbs into a vacuum cleaner nozzle covered with cheesecloth. Be careful to avoid patchy cleaning or overcleaning.
Adhesive rubber (e.g. Groomstick) is a natural rubber product that is very sticky and attractive to dirt. Press it gently onto the surface (do not rub); as it becomes blackened by dirt it can be torn open to reveal a fresh, tacky surface. Work slowly and regularly compare the cleaned surface with the untreated areas around it, aiming for consistency in appearance. This material is very efficient so take care to avoid overcleaning.
Where the above treatments prove either ineffective or too time-consuming, a solid gum eraser can be used. Gum erasers are made of natural rubber and are milder than those made of PVC or filled rubber. Remove eraser crumbs by brushing them into a vacuum cleaner nozzle covered with cheesecloth. Do not overclean.
This technique should be used only when all else has proved unsatisfactory. Wet a small cotton swab with distilled water and squeeze it almost dry. Apply the swab to the surface with a rolling motion, thus lifting dirt off but depositing very little water. Discard the swab as soon as it becomes soiled and continue with a new one.
Figure 1. The effect of abrasive cleaning on wood. Because the early growth has larger, softer cells than the later growth (which has denser, tougher cells), overcleaning can exaggerate grain patterns.
Before cleaning a bare wooden surface it is important to decide why this needs to be done and what the surface will look like afterward. As all cleaning techniques are potentially damaging to wooden surfaces, conduct preliminary tests on unobtrusive areas and carry out the cleaning slowly and carefully. The freshly cleaned surface will be very reactive to its environment and will demand continuing attention to keep it clean.
Brushes and eraser products:
- Local art supply stores
- Conservation supply companies
- Crafts Council. Science for Conservators: Conservation Science Teaching Series. Volume 2: Cleaning. London, UK: Routledge/The Conservation Unit of the Museums & Galleries Commission, 1992.
Copies are also available in French.
Le présent texte est également
publié en français.
©Minister of Public Works and Government Services, Canada, 2002
Cat. No. NM95-57/7-1-2002E