"It is an important professional responsibility to ensure that all items accepted temporarily or permanently by the museum are properly and fully documented to facilitate provenance, identification, condition and treatment." (ICOM Code of Professional Ethics, 1990, p. 31, nr. 6.2)

CIDOC fact sheets are produced to disseminate, in a simple format, information on aspects of museum documentation. This fact sheet is concerned with the methods used for labelling and marking of objects with their accession or inventory number. The methods to apply the number to the object are not always agreed upon. However, there are some rules generally accepted in the museum community. As this fact sheet can only give summerised information, it concludes with some literature for further reading.

General rules

• Numbers (eg. inventory or accession number) are the connection between objects and documents related to them. They must therefore be physically attached or applied to the objects.
• When an object is or becomes part of the collection, it receives an accession number. To apply the number to the object a secure method should be used, which means the method should be safe for the object while ensuring that the number cannot be accidentally removed.
• If a temporary number (e.g. a loan number) has to be assoicated with an object, tags can be used.
• Labelling and marking of objects should be done in a consistent manner, by trained employees. Enough time should be allowed to examine the object, to clean the surface using a suitable method and to apply the number.
• When doubt about the right method arises, a restorer should be consulted. It should be noted that no given method can be considered entirely safe and that some of the products and methods most frequently in use have not yet been systematically tested.
• A number should be applied without causing damage to the object. At the same time it should be possible to remove the number safely, even though for security reasons museums like to consider using a permanent mark.
• The number should be easy to locate without unnecessary handling of the object and at the same time without defacing any aspect of the object likely to be displayed or photographed.
• Although different types of objects have their own requirements for numbering, it is recommended that the range of methods and materials in use be kept to a minimum.
• When an object is made of several materials (e.g. paintings, uniforms, furniture), the number should be applied to the most secure place, given the method used.
• When an object consists of several components likely to be dismantled or separated, each part should be numbered. The same applies to fragments of a broken object.
• A museum should set out its numbering rules (including rules for number formats) in a report that is made available to all relevant staff members.

Do not:

• remove old numbers, as they can give information on the history of the object. If this cannot be avoided, the old number(s) should be recorded in the documentation.

Position

• As far as possible, numbers should be applied to the same position on a given type of object, so as to avoid unnecessary handling. Fragile or heavy objects should not have to be picked up to find the number. Large objects might need to be numbered in more than one place or to have extra temporary paper tags when not on display. If an object is stored in a box or wrapped up, the number should be repeated on the packaging material.
• The number should be placed in a position where it does not unduly affect the object's appearance. It should not, for example, obscure any legend or other marking intrinsic to the object.
• Small objects pose specific numbering problems. To some objects only a distinctive part of the number can be applied. When an object cannot be numbered at all, a number should be applied to the object's packaging, though this is not an entirely safe solution.
• In order to avoid accidental removal of the number, it should not be applied to physically unstable surfaces or parts that are subject to wear or friction.

Do not:

• number large, heavy or fragile objects on the bottom

Methods

• In applying a number to the object, the methods and materials used should not involve a risk of permanent damage for the object.
• Long-term reversibility should be ensured, while the number itself should be long lasting. Although the use of tags is the least intrusive method for the object, marking the number directly on the object, when practicable, is a more reliable process.
• The number should be easily readable. Generally, black characters are used on a light background, white characters on a dark background. Red characters may be considered as an alternative for both types of backgrounds.
• To increase the security of the link between the object and its documentation, it is recommended to include the number in some of the object's photographs.

To mark the object, specific methods should be used, depending on the object's physical aspects:

• On hard, non porous surfaces, the number should be written in drawing ink (water soluble non acidic) or acrylic paint. A coat of acrylic varnish can be applied on the cleaned surface, as well as on top to protect the number. (Examples: glass, glazed pottery, metal)
• On hard, porous surfaces, the same method should be applied. However, the cleaned surface should always be protected by a coat of acrylic varnish before the number is written. (Examples: wood, terra-cotta, bone)
• On paper products, the number should be marked lightly with a soft pencil. (Examples: prints, photographs, books)
• On textiles, prenumbered cloth labels should be sewn onto the object with a few stitches, using a fine needle and compatible thread. (Examples: costumes, lace, rugs)
• Painted and lacquered surfaces, as well as plastics, should be handled with special care, because they may be sensitive to the materials usually used for numbering objects.

Do not:

• burn or scratch the numbers on wood or metal
• screw a metal plate on wood
• use stamps or ink on paper products
• use ink or paint on textiles
• apply adhesive labels (including barcode labels) without protective coating on any material
• use metal edged tags or wires
• use as a base coat products which are originally intended for significantly different purposes and materials, especially when the composition of the product is not clear (e.g. correction fluid, nail-polish).