Annals of preservation

Technology gives new life to cultural relics

By Eric Leung

Although dug up in pieces, many cultural relics are well-preserved in Hong Kong by the Central Conservation Section.

According to Miss Alice Tsang, the curator of the Hong Kong Museum of History, there are eight main types of collections being preserved by the section.

They are paintings, documents and manuscripts, textiles and specimens, prints and photographs, metals, organic materials, archeological finds and ceramics.

Under the section, three laboratories carry out preservation work.

They are located at the Hong Kong Museum of History, the Hong Kong Heritage Museum and the Hong Kong Museum of Art.

Preservation requires keeping cultural relics in a stable environment with stable temperatures and relative humidity, so as to increase their lifespan.

According to Miss Elisa Leung, assistant curator, the method of preservation differs among cultural relics.

Metals are stored in a dry environment at about 40 percent relative humidity because high relative humidity speeds up the corrosion of the metals and tarnishes them.

Paper is stored in about 50 to 60 percent relative humidity.

Fractures appear if it is too dry, and fungus will grow if it is too humid.

In any case, the conditions must be stable.

Miss Tsang said great fluctuations in conditions might result in the alteration of the shape of the relics.

Prolonged expansion and contraction of small fractures may eventually lead to irreversible distortion of relics.

To provide stable conditions, several methods are employed by the museums.

A monitoring system composed of a sensor and a receiver has been installed in museums to check temperature and relative humidity.

The Hong Kong Museum of History monitors the conditions in the Lei Cheng Uk Han Tomb Museum and the Hong Kong Museum of Coastal Defence through this system, Miss Leung said.

A microclimate using buffering agents maintains a constant relative humidity.

Buffering agents such as silica gel help absorb moisture when the relative humidity is too high and vice versa.

Mountings and supports like archival boxes and museum boards are also provided for some cultural relics for display.

Miss Tsang said archival boxes are made of acid-free museum board.

Museum board is used to make mounts for photographs to avoid damaging edges.

Several methods are used to protect relics from ultra-violet light and pollutants, which may cause relics to fade.

So, UV-free light, such as tungsten light, is used in the museums.

Curtains and films are also used to screen sunlight from entering the windows, Miss Tsang said.

Apart from these, the museums have charcoal filters and chemical filters in their air-conditioning systems for protecting metal or paper relics from acidic pollutants like sulphur dioxide and nitrogen oxides.

A new technology, encapsulation, also helps in the preservation work.

Encapsulation keeping paper in a plastic capsule composed of two polyester plastic sheets.

The four sides of the sheets are welded by an ultrasonic wave to form the capsule.

In this way, two-sided tapes or glue that may damage the relics are not necessary, said Miss Tsang.

Said Miss Tsang: “A replica is made for those ‘vulnerable’ cultural relics.

“But we always inform visitors whenever the collection is a replica.”

Conservation, said Miss Leung, means repairing the relics whenever damaged.

According to her, repairs are used to stabilise a relic, improve its integrity or reveal its original appearance.

A condition inspection is used to analyse the material and pigment of the damaged relic before applying treatment.

A fourier-transformed infra-red spectrometer is used to check what original material the relic was made of.

Said Miss Tsang; “For example, we use similar fibres to repair a paper artefact.

“UV glue or mould is useful in repairing broken glass.”

Apart from conservation, the section also carries out constant check-ups of the cultural relics in Hong Kong.

Said Miss Tsang: “Sculptures along the Tsim Sha Tsui coast are checked from time to time.

“So are the museums like Sam Tung Uk Museum.

“They are also checked constantly and some maintenance work such as debugging and cleaning the furniture is done.”