北疆博物院館藏古生物化石標本的預防性保護

崔冠瑜

Abstract The preservation of fossil specimens has gained increasing attention and the exploration of scientific and effective methods has never stopped. Hoangho Paiho Museum is a good case in point. Its exploration of systematic measures to preserve the fossil specimens it collects has made contribution to the practice and theory in this field.

Keywords fossils， preventive protection， Hoangho Paiho Museum

0 Introductions

Hoangho Paiho Museum， which was established by Emile Licent in 1914， is the predecessor of Tianjin Natural History Museum and is affiliated to it now. Emile Licent collected about 200 000 fossil specimens， including fossils of ancient plants， animals， humans and ores. They still have great value in scientific research and education. In the past century， the fossils have experienced wars and natural disasters， and are crying for proper maintenance. Since the museum was reopened in 2016， the fossils stored and displayed in it have been under proper preservation， from reinforcing some diseased specimens and making safe containers for the specimens to monitoring and controlling the temperature and humidity conditions of the warehouse.

Fossils are non-renewable geological relics created by geological movements. As the specialists in this field fully understand the value of fossils， they have changed the passive rescue maintenance into proactive protection. Hoangho Paiho Museum follows the theory and practice， and has decided to strengthen the maintenance of the fossils， which involves reinforcing all the diseased fossil specimens， making containers tailored to each specimen as well as controlling and monitoring the temperature and humidity conditions of the warehouse.

1 The present state of the fossil specimens in Hoangho Paiho Museum

Hoangho Paiho Museum possesses more than 5 000 fossil specimens， among which 177 are regarded as the first or second level of protection of fossil. Most of them were collected by Emile Licent in 14 provinces alongside Yellow River， Baihe River， Luanhe River and Liaohe River prior to 1930s and have important historical and scientific values. Through so many years after being unearthed， experiencing the Anti-Japanese War， several floods and various natural disasters， the specimens are in poor conditions to different degrees.

The troubles that the specimens are faced with are as follows. （1）The surface or interior of some specimens turns into powder. （2）Dirt， mud or marks of glue or varnish left on some specimens can hardly be removed. （3）Some specimens have fissures or have fractured. （4）The surface of some specimens flakes off due to some unfavorable causes. （5）Parts of some specimens are gone due to one or more of the above-mentioned causes.

2 Some serious unfavorable external factors facing the preservation of the specimens

Specimens may be affected by various adverse factors， most of which are external ones.

Most of the fossils collected by museums had existed either on the surface or in shallow layers of the earth due to crustal movements before they were uncovered. They might have been weathered by natural adverse forces like wind， rain or water erosion. Thus， the preservation of fossil specimens is a delicate and tough task.

In recent years， the air pollution problem facing China becomes increasingly serious and is worsened by frequent heavy smog in many parts of the country. Whats worse， the preservation of fossil specimens has been plagued by another problem resulting from decoration pollution. With the development of museums in China， the construction or expansion of natural history museums have been carried out in full swing. Most of the modern decoration materials used in exhibition halls and warehouses fail to meet the environmental requirements for museums. Besides， organic curing agent used to reinforce specimens tends to lead to the rise of volatile organic compounds in warehouses. Unfortunately， fossil specimens are vulnerable to air pollutants and the toxic substances in decoration materials.[3]

In addition， fossil specimens should stay in proper temperature and humidity conditions： temperature from 22°C to 25°C and humidity from 45% to 55%. The control of humidity is more important than that of temperature. Low humidity is likely to lead to deformation， flaking or rupture of fossil specimens while high humidity may cause fossils to absorb water， which tends to result in the rise of moisture and internal pressure of fossils， thus making them lack hardness. The cycle of hydration and hydrolysis will lead to fracture of fossils. Some museums built many years ago do not have good water-resistant walls and floors and often cannot keep the humidity controllers working for enough time for the reason of safety or cost. Therefore， it is difficult to keep the fossils staying in stable and proper humidity conditions there.

Infrared light can raise the surface temperature and reduce the humidity of fossils， which may change the internal pressure of fossils， and accelerate weathering. Ultraviolet light can photolyze the polymer curing agent used in the repair of fossils and in turn do harm to the fossils.

Fossil specimens often need to be reinforced on the site when specialists unearth them or do some scientific identification or research. But not all the reinforcement measures can meet the requirements for permanent preservation. Fossils with different chemical compositions and structures or unearthed from different strata which have different lithology and weathering degrees entail different curing agents and reinforcement methods. Therefore， the temporary protective measures taken in the field may challenge the permanent preservation and the replacement of out-dated reinforcing materials with new ones is badly needed.

3 Preventive maintenance measures

Generally， preventive maintenance work involves two steps. First， assessing the risks of the specimens. Second， if risks are found， the specialists will take necessary measures to get rid of them or reduce future degeneration. Take the maintenance of the mammal fossils in Hoangho Paiho Museum. The work is done in following steps：

（1）Examining the diseases the fossils suffer from

Through examining the fossil specimens， the specialists found most of them suffering from one or more above-mentioned diseases， of which powdering ranks the first.

（2）Working out specific maintenance schemes

With the help of some specialists from Tianjin Natural History Museum， the team has worked out specific protective schemes for our specimens. Firstly， maintaining appropriate temperature and humidity conditions has been given the first priority. The museum has been trying to make best use of its temperature and humidity monitoring and controlling systems to ensure that the specimens stay in proper temperature and humidity conditions around the clock. Secondly， the team suggests that enough fossil containers be made to ensure that the specimens are safe when undergoing scientific research and routine security check. Thirdly， while the specialists treat the diseases of the fossils， they are supposed to make records in forms of both words and pictures which can help them keep track of the curing effects in future.

（3）Implementing the maintenance schemes

The maintenance of fossils is different from that of historical relics. The ages of fossils are far older than any historical relics so they are vulnerable to unfavorable conditions， particularly external forces. The specialists have to take some preventive measures prior to specific repair work.

Fossil maintenance work requires careful treatment like that of historical relics. Most of the maintenance work is actually irreversible although the materials and methods themselves are reversible. The negative effects on the fossils can hardly be removed completely， which may affect the specimens value for research and display. Therefore， the materials and tools used for the maintenance work must be strictly selected so as to minimize the possible negative effects. This work also requires that the specialists who perform it have patience， meticulousness and fine skills， which are indispensable to the task.

When examining the diseases of the specimens， the specialists found that the color and texture of the reinforcing agent used before had changed so they decided to replace it with a more stable and durable kind of agent. Some experts of Institute of Vertebrate Paleontology and Paleoanthropology were invited to the museum to join in the discussion about the maintenance work. They suggested that we should use another kind of reinforcing agent named “Paraloid”， which has been widely used in IVPP and aboard. “Paraloid” uses organic solution as solvent， so no aqueous solution is needed. It does not have the delayed effect of color change and does not form a film on the surface of the fossils. In addition， the curing agent can quickly reach the interior of the fossils and glue the broken parts together， thus effectively enhancing the internal hardness of the fossils. As the collections of the museum had stayed in different natural conditions and weathered to different degrees before being unearthed， they should be treated differently in the maintenance process.

Special containers tailored to each specimen are made with PEP material. Consequently， before being stored in the containers， the specimens must be laid in a dark and well-ventilated place for more than 48 hours so that the solvents that are harmful to the health of the staff can volatilize completely.

The maintenance team is supposed to keep records of its work by taking pictures and making notes before and after doing the repair work for any inquiry about it in future.

4 Conclusions

To ensure the safety and good storing conditions of the collections is part of the most important work of our museum， which is the prerequisite to the display and research of the fossil specimens. The preservation of fossil specimens， unlike that of historical relics， still lacks experience in reliable systematic maintenance throughout the country. Our museum has been trying to explore reliable and effective ways to preserve our fossil specimens in the systematic maintenance work and has made much progress， which helps improve the work in both practice and theory.

References

[1]ZHENG J C， LI Q K. A review of centennial history of Hoangho Paiho Museum[J]. Art and Literature for the Masses， 2011（21）： 218-221.

[2]XU H B. The pathogenic mechanism and conservation study on fossil ivory of Chengcheng County[D]. Xian： Northwest University， 2012.

[3]REN Y Q. A preliminary analysis of protection of geological specimens[C]. Custody Specialty of Beijing Museum Societys Ten Years Research Commemorative， 2010.

[4]ZHAO G X， PENG G Q. A discussion on preventative conservation of stony cultural relics in museums[C]. Annual meeting of Society of Vertebrate Paleontology of China， 2014.