西汉帝陵

　　汉景帝阳陵的考古发掘揭示了汉代社会、历史、文化及科学技术的发展状况；帝陵博物馆的建设，成为一个集考古发掘、研究展示、文物保护于一体的综合性博物馆；而汉阳陵文物展示方式与保护理念的探讨，则为未来遗址博物馆文物保护与展示利用提供了新的思路与借鉴作用。
　　汉阳陵帝陵博物馆的建设，以及与之密切联系的文物保护工作，是多种综合因素的结合体，涉及到：复杂的文物环境(包括埋藏与出土的环境)；特殊的出土文物类型；现阶段文物保护技术方法的局限性；以及尝试建立封闭保护体系对文物产生的影响及作用评价等方面。因而说，汉阳陵现场文物保护与展示方式具有典型的研究意义和探讨价值。
　　一、汉阳陵出土文物遗迹的形成及类型
　　阳陵的出土文物之所以难以保护，同它特殊的文物类型与所处环境有很大关系，除去各式各样的陶俑及动物俑，以及数量有限的各类金属文物和玉器外，普遍保留下来的是大量有机质文物遗迹(木质和木质彩绘、漆木、纺织品、骨骼等文物)。这类文物遗迹形成的原因主要为：不适宜的埋藏环境，导致其快速腐烂，而土壤颗粒或矿物质成分在水及其他地质营力的作用下，同时填充到有机质槽朽降解后留下的空间，这一连续转变的过程，最终使土壤颗粒或矿物质置换有机质文物，形成了经考古发掘仔细清理后，基本保持原始形状，但已不具有原有文物性质的土质化文物遗迹。这种遗迹状况的保护，目前还没有非常好的办法提取，如果原址保存，其难点在于这类文物受现场条件影响最大、保护矛盾非常突出，缺乏主动的应对办法，往往处于自生自灭的状态之中。
　　汉阳陵作为遗址博物馆，其出土文物中保护矛盾比较突出的包括：
　　1．大量的木质及木质彩绘的遗迹，它是阳陵出土文物的重要组成，这类木质和木质彩绘文物占有相当大的比例，是除各式陶俑以外汉阳陵的又一特色出土文物。但是汉阳陵所处地理位置——陕西咸阳塬上不干不湿的北方埋藏环境，不具备长期保存的良好条件，同其他有机质文物一样，土壤颗粒或矿物质置换各类木材而变为土质车马、或者是土质彩绘车马，而考古发掘保留的是根据遗迹现象仔细清理后，仅存器形的土质车辆及原来用木材雕刻成的土质马匹等文物遗迹现象，它是土质化文物遗迹的典型代表。这些遗迹原始形状清晰可见，由于上述土壤化过程使其质地结构蔬松、脆弱且不定型，只有通过遗迹遗物现场部分展示的方式，将这些有型而不成器的残留土质文物遗迹长期保存。
　　2．漆木器文物(木胎、夹苎胎的漆木箱、漆木盒等)的残留表面漆皮，虽然早已残破不堪，但作为历史遗物的鉴证也具有重要的保留价值，这些文物的出土随着考古发掘的进行将其暴露在自然条件下，则失水开裂变形卷曲的情况非常严重，这样的文物保护难题，与周边文物环境具有无法分割的关联，只有就地将这类遗迹保存。其它的漆质文物如陶器表面用于施彩的一层底漆也随着逐渐暴露，而使漆层老化加速、干燥收缩，随之彩绘脱落。
　　3．就是相当数量的彩绘文物(包括动物俑、陶器等)，主要是K-13号出土有大量造型各异、制作精湛动物俑群，以猪、狗、羊、牛等为代表，颜色分别为红、黄、白、黑、褐色组成，另外还有彩绘陶俑、大型彩绘陶仓。这些文物的保护如果处在实验室条件下，都能得到妥善的处理，但是野外现场展示，使文物长期处于极端的环境条件下，将会导致彩绘褪色，再者文物与地下泥土紧密相联，常规化学保护方法受到限制，无法从根本上解决它的保护问题。
　　二、汉阳陵现场文物存在的主要问题
　　除去汉阳陵特殊的出土文物，外部环境因素直接对文物的保存产生作用。在帝陵博物馆建设之前，考古发掘现场文物的基本状况是，采取钢结构匡架支撑、以玻璃钢瓦作顶棚，它的作用仅限于防止雨水直接冲刷和阳光嚗晒，其它方面的防护作用不明显。通过对帝陵现场文物保存环境的调查研究，结果显示存在着许多不利因素，主要表现在以下几方面：
　　1．温湿度的剧烈变化：温湿度的作用在于促进各种文物破坏反应的进行，是文物遭受损害的根本因素。而阳陵发掘现场近似露天的条件下，温湿度也自然随着一天的变化而随时波动，根据温湿度监测记录显示，日气温波动范围达20℃以上、湿度变化超过30％～40％，特别是冬夏两季面临着持续高温和寒冬结冻造成文物的物理性破坏；其剧变而引发的木质遗迹文物失水开裂；以及化学作用和微生物生长等的诱因都源自温湿度剧变。
　　2．坑壁坍塌：阳陵地处咸阳原上，地质形成较晚，为三级失陷性黄土，这种土壤结构松散，含沙量较大，故极易开裂，失水收缩量大，因此将形成塌陷，起壳、脱落。近两年多来，坑壁四周多处塌落且形势愈发危急，直接影响到现场文物的安全和游客的人身安全，这已成为阳陵的重大隐患之一。
　　3．光线及紫外线的辐射：对于现场文物来说顶棚的玻璃钢瓦仅能挡住一部分可见光，强烈的紫外辐射穿透顶棚直接作用到文物表面，一方面产生光化学反应引起彩绘的褪变同时促进坑内有机质文物的分解，直接、间接的起到破坏作用，从目前来看已有的彩绘出现褪变色，许多漆器的残留物出现酥解。
　　4．降尘及风沙的作用：咸阳原是西安以北的一道天然屏障，而对处于原上的阳陵文物来讲降尘及风砂的破坏作用较其它地方明显，除去机械磨损的破坏、文物表面的风化，空气尘埃降落于文物表面成为有害气体、微生物的载体而产生作用，并影响到文物的观赏性。
　　5．动物昆虫的破坏：在划定保护范围之前，发掘现场为种植农田。经考古发掘后，由于文物中有大量的木质文物和坑道木框架，经常年腐化，遗迹的腐殖物形成了坑道独特的营养生态条件，且周边杂草丛生及现场安全需要的灯光，诱集了大量的农田害虫以蟋蟀类、蝼蛄类、鼠类进入坑道的威胁、破坏严重，它们发生数量大，在文物上钻洞造巢，栖息、取食、爬行划痕、粪便污染，目前已对这类文物造成了许多伤害。
　　6．微生物、低等植物的大量滋生。同上原因，坑道独特的生态环境，使微生物自身需求得到满足的内因，及环境下高温高湿的外部条件和目前为了保护文物环境的相对稳定所采取覆盖塑料布的因素，在阳陵造成了大量微生物、低等植物的泛滥，也成为危及文物安全的重要隐患。
　　三、现场文物遗迹保护的原则及难点
　　汉阳陵出土的土质化遗迹和其他考古发掘出土物，是在汉阳陵历史背景下形成的特殊文物，出于文物保护的需求和不脱离文物原址环境为出发点，原址保护就成为汉阳陵遗址风貌保护总体规划的重要内容。自汉阳陵考古发掘以来，在文物保护与遗物展示利用中，始终坚持在进行考古发掘的同时注重实物遗存的保留与保护；尽可能减少直接干预；完整保留现存实物原状与原始历史信息；在具体出土文物的保护中以预防灾害侵袭；降低环境因素带来的损伤；并且根据文物特性的要求合理使用技术等等，这些成为现场遗迹、遗物保护遵循的基本原则。
　　汉阳陵遗迹、遗物的保护是在现场特殊环境下开展的专业技术工作，现场环境条件的各种影响无法回避，同许多室内保护工作相比，从事田野保护会因操作条件的不确定性而影响到保护工作的最终结果，从某种意义上讲，外界环境条件会起到决定性作用。如阳陵木质及木质彩绘遗迹的加固，在实验室内能得到妥善处理，但是在现场加固中，更应考虑加固材料的合理性与适用性，以满足复杂情况下对材料的要求，主要涉及材料与水的兼容性、具备优良的透气性、耐候性、渗透性，还有在加固过程中保持土质表面不产生失水开裂，目前来看，现有的保护技术和材料，无法达到满意效果，其原因就是无法排除现场外界环境条件的作用。类似的问题又如微生物的生长、虫害的繁殖，都不会孤立的存在，往往周边联系紧密，无形中加大了问题的困难程度，甚至有些目前根本无法解决。
　　四、原址展示与保护方法的尝试
　　文物埋藏初始阶段，在地下经过一段时间，随着埋藏环境趋于稳定，文物就处于一个相对、暂时的动态平衡之中，但是随着发掘进行固有平衡被破坏，特别是温湿度骤变、光辐射等对文物产生一突变过程。成为文物毁坏的直接诱因，加之出土后环境条件的反复波动，增大了破坏反应的进行，不利于文物的长久保存。因此，文物所处环境研究成为文物保护中的一个新课题，最新的研究成果也显示，对文物实施保护的最有效平段就是控制文物所处环境，为文物营造一个相对稳定、单独存在的空间。
　　汉阳陵帝陵丛葬坑博物馆的建设理念中，其下沉式地下现场展示也是其于环境因素的考虑，将着眼点放在营造较为稳定的现场环境，即通过恒定文物所处小环境来达到阻止出土文物免遭破坏的目的。从稳定的文物环境所产生的实际效果来看，加之先前南区从葬坑8号坑文物保护示范工程的应用实例说明，封闭式环境控制保护方法，能很好的达到了阻止温度剧烈波动；长期保持平衡的高湿度条件；具备隔离人为活动干扰文物环境平衡，阻隔污染物带入渠道等的作用。在缓解失水开裂，减少霉菌污染，延缓土遗址风化速率等方面作用积极。
　　五、汉阳陵文物保护模式的积极作用
　　汉阳陵特殊的文物类型及其所处环境状况的恶劣，依现行的文物保护方法与技术去解决它，还存在着许多困难。实施这种封闭式的保护方法。使客观存在的保护难题得以规避。这种及时控制和协调，有助于消除文物的埋藏与保存环境间巨大的反差，使文物由埋藏环境平稳、安全过渡到出土后的保存环境中，相应使出土文物得到有效保护。该方法的应用是为了解决汉阳陵文物面临的具体问题，它特别对汉阳陵大量有机质文物的保护起到了明显的作用。
　　通过汉阳陵范围内文物状况、展示效果的分析与调查，封闭式文物保护模式起到了很好的效果，这种方法是一种文物保护与文物展示方式的有益尝试，具有重要的参考价值，会为类似性质的工作的开展提供有益的借鉴，产生的积极作用包括：
　　1．使文物埋藏与保存环境得到和谐、统一，消弱了外部环境对文物产生影响的程度，最大化的使文物保持相对稳定状态。
　　2．从文物的现状与病害情况出发，按照文物保存的具体情况，使文物保护存在的矛盾得以缓解，文物病害得到抑制，使文物保护具有针对性。
　　3．将文物保存空间与人行参观空间进行分离，使不同类别对环境的需求得到满足，避免人为活动产生和带入危害物质侵蚀文物本体。
　　4．作为文物保护的另一种模式与方法，汉阳陵存在的问题，在遗址类文物出土中具有普遍性。因此它的尝试与试验结果，为深入研究、探讨遗址类文物的保护方法提供借鉴。
　　Thoughts on the Protection and Exhibition of the Unearthed Relics in Han Yangling
　　Zhao Xichen(Shaanxi Archaeological Research Institute)
　　The archaeological excavation of Han Yangling Mausoleum Complex(HYMC)revealed the develop-ment level of society,history,culture,and science of the Han Dynasty.Han Yangling Museum(HYM)has evolved into a comprehensive museum with a combined function of archaeological excavation,exhibition and study,and preservation of cultural relics.The ongoing discussion of the display style and the protection philosophy furnishes adequate information for the future development of the museum.
　　The construction of the HYM and the preservation of the relics are a combination of four composite fac-tors.It involves the intricate environment of cultural property(including the burial and the preservation en-vironment);the idiographic types of unearthed objects;the limitations of the current applicable preservation technology;and the influence over the relics by the enclosed protection system.Therefore,significant value and importance are essential elements in the related research and discussions of the protection method and display arrangement at HYM.
　　I.The Formation and Types of the Cultural Relics Unearthed from HYMC
　　The primary obstacle in the preservation of relics is the special type of objects and the surrounding en-vironment.Besides various pottery warriors and pottery animals and some metal wares and jade wares of different types,the majority of the excavated items are organic relics(wooden wares and wooden color paintings,lacquer wares,textiles and ossature).The cause of formation for this type of relic was the un-favorable burial environment and conditions,which led to the rapid decomposition of the object.Soil par-ticles or minerals,being effected by water and the external geologic conditions,filled the spaces created after the decomposition of the organic matter.After a series of consecutive conversions,eventually the soil particles or minerals displaced the organic relic and formed a new type of relic-terrene relic.The new type of terrene relic,after excavation and treatment,generally retained their initial appearance,but forfeited their primary nature.Currently there is no optimal approach available to protect this type of relic.If“in situ preservation”method is selected,then several barriers prevent solution: Maximum site condition limit,acute preservation imbalances,and the lack of active coping plan.
　　At the Han Yangling Archaeological Exhibition Hall,the concentrated expression of the acute preser-vation imbalances of the unearthed relic includes the following aspects:
　　1.Massive wooden wares and wooden color paintings constitute the major part of the excavations.Cultural relics of this type are distinctive as is the diversified pottery figures unearthed at HYMC.The ge-ographical location of HYMC determines that the burial environment here in northern China is not ideal for the long-term conservation of buried articles.Like the other organic relics,the soil particles or minerals displaced the wooden relics and shaped them into terrene chariots and horses or terrene painted chariots and horses.So after the excavation and treatment,the result was only the shape of the terrene chariots and the original sculptured wooden horses.This type of relic is the typical representative of terrene cultural ruins.The initial shapes of these relics are still visible but the process of the displacement made the objects porous,frail,and shapeless,which makes live demonstration the only method applicable.
　　2.The coat of paint left on the surface of the lacquer wares(lacquer trunks and cases with wood or cloth mould)is dilapidated but still bears significant value as the testimony of history.The progress of the excavation exposes the lacquer wares to natural circumstances,which causes severe desiccation,cracking,deformation,and crispation to the paint's surface.Some other painted relics,such as pottery,suffer from the same cause.Hence,the“in situ”preservation is a sensible choice.
　　3.A considerable number of color painted relics(including pottery animals and pottery wares)with exquisite craftwork unearthed at HYMC created a problem in preservation as well.Pit K-13 is where most of the color-painted relics were excavated.Besides the painted pottery warriors and pottery barns other master-pieces found there are hordes of pigs,dogs,sheep,and cattle.The prevalent colors are red,yellow,white,black,and brown.If placed in laboratories,these relics will be handled appropriately.But the field display will expose the relics to harsh conditions and the paint will eventually fade.Another issue is that the relics are all deeply buried and the routine chemical protection method was restricted in its full function.
　　Ⅱ.Major Problems
　　The exterior environment is another element that affects the relics.The structure of the excavation site,before the construction of the Protection Hall of Secondary Burial Pits(Underground Museum),was a roof of glass steel tiles sustained by steel brackets.This can only free the relics from the rain-wash and direct ex-posure to the sun.Some adverse factors appeared after an inspection conducted at the Emperor's Tomb.The following are the major ones:
　　1.Wide temperature and humidity swings.Temperature and humidity are the facilitators of the de-structive actions that could have a negative impact on the relics.In other words,temperature and humidity are the root cause for damaging the relics.The excavation at HYMC proceeds under the circumstances that closely approximate the natural environment,hence,the value of temperature and humidity always fluctuates.Statistics show that the range of the temperature change reaches more than 20℃ and the variations of hum-idity exceeds 30 to 40 percent.The continuous heat in summers and the winter frosts result in some serious physical damage to the relics.The temperature and humidity fluctuation is also induces various chemical re-actions and the development of microorganisms.
　　2.Collapse of the walls in the pits.HYMC is located on the Xianyang Plain,where the geological formation was completed relatively late.The soil type is classified as the third grade subsidence loess.The soil structure is loose and file sand content is high,which causes the surface of the ground to craze easily,thus,collapse,flake,and shed are risks associated to the pit walls during the past two years.Some areas have started to compromise the safety of the relics as well as the tourists-and this becomes one of the latent dangers.
　　3.Lighting and ultraviolet radiation.The roof of glass steel tiles can only block a portion of the visible light but the blazing ultraviolet light can still penetrate the tiles and strike the surface of the relics.This stimu-lates the photochemical reaction that will cause the coated paint on the relics to fade and will accelerate the resolution of the organic matter in the pits,which is what happened to some of the color paintings and lacquer wares.
　　4.Dust and sand storm.The Xianyang Plain provides a natural defense for Xi'an but the relics at HYMC are susceptible to damages by the dust and sand storms that frequent the plain.Aside from the mech-anical wear and the weathering,noxious air and microorganisms carried by dust and sand storms begin to disrupt the appearance of the relics.
　　5.Damages caused by animals and insects.In the pits there are wooden relics and wood frames,which have been decaying for a long time.The humus of these wooden wares formed a unique nutritional ecological circle in the pits.The location of the museum used to be croplands,so the lights at the excavation site and the special ecological circle attract field pests,e.g.,crickets and field rats.The entering pests will nest,inhabit,and forage in the pits,which put the relics at various risks like crawling scratches and fecal con-tamination.
　　6.Growth of microorganisms and lower plants.This is caused by the same reason above,which is the unique ecological environment inside the pits.It suffices all the requirements of the microorganisms.The calculated temperature and humidity inside the museum provide the microorganisms and lower plants with more favorable conditions.And the problem caused by this is in dire need of proper solutions.
　　Ⅲ.The Principle and the Difficulties of the Preservation.
　　The terrene relics and other excavations at HYMC are the unique cultural heritage items produced by the historical background.Considering the relics'demands for preservation and the connection between the unearthed items and the site,“in situ”preservation is the main method used in the overall plan.Since the discovery of Han Yangling,the archaeologists'unremitting effort has been made to protect and display the relics in an optimal fashion.The basic principles are to improve the conservation and preservation approa-ches;to eliminate direct interference;to keep the intact form and the original historical information of the entity;to prevent the relics from unexpected emergencies,and to employ the proper technology in accordance with the features of specific relics.
　　The excavation at HYMC is conducted on site and some situations are hard to predict during the field operation.The outcome of the project mainly depends on actual performance.To some extent the exterior environment is the decisive factor,e.g,the reinforcement of the wooden wares and the wooden painted relics.This type of relic can be handled properly if placed in a laboratory.But when the reinforcement work is carried out on site,the applicability of the reinforcing material selected must be taken into consideration.It involves the compatibility of the material with water,its breathability,weatherability and permeability,Moreover,attention needs to be given to keep the terrene surface from crazing.The reason that the current technology and material cannot achieve a desirable level is that the effect of the exterior conditions is not eliminable.The growth of microorganisms and the pests reproduction are part of the problems as well.All these different factors of the problem cannot be viewed or solved separately,which makes it even more dif-ficult to find the final solution.
　　Ⅳ.Attempt on the“in situ”Display and Preservation
　　All the underground relics have reached a relatively balanced stage temporarily after being buried for a long time.The excavation will break the balance and changes the physical feature of the relics together with the temperature and humidity fluctuation and the ultraviolet radiation.The repeated swings of the exterior environment after the excavation even worsen the reaction,which is not favorable for the preservation of the relics.So the environment the relics are exposed to becomes a new task.The new research findings show that the most effective approach of the protection of the cultural heritage is to have control over the en-vironment,so as to develop a relatively stabilized and individual space for the unearthed treasures.
　　The construction plan for the southern and northern sections of the Emperor's Tomb pits also takes the environmental element into consideration and aims to create a stable site condition for the relics,The sub-sidence style display arrangement is designed to develop a constant microenvironment to prevent the unearth-ed items from damage.Judging from the practieal effect after applying this method and the success of No.8 Pit at the southern section pits,the enclosed protection way is currently the most serviceable one.It can better regulate the temperature,constantly maintain the high humidity,and insulate the possible harm caused by human activities and contamination.The enclosed preservation method also has satisfactory performance in alleviating cracking,decreasing contamination,and deferring the velocity of weathering.
　　Ⅴ.The Positive Effect of the Protection Style at HYMC
　　The type of relics and the harsh environment make it unrealistic to preserve HYMC and the relics un-earthed with any regular method and technology.The attempt of the enclosed preservation system mitigates many objective problems.It promptly supervises and adjusts the environmental changes;eliminates the differences between the underground and practical environments;and smoothes the transition from the under-ground situation to the practical circumstances.Hence,the relics can be protected effectively.The application of this preservation system is to solve the concrete problems confronted by the museum.
　　The steady relics'condition and the delightful display arrangement are the vivid proofs of the achie-vement accomplished by the enclosed protection system.Analysis and inspection conducted illustrate that this method is successful and it has significant referential values.Meanwhile,it will provide guidance for the similar projects.
　　The positive effect of the enclosed protection method includes:
　　1.Harmonize the underground environment with the preservation circumstance;eliminate the exterior influence over the relics;and keep the cultural relics under a stable condition.
　　2.Alleviate the conflict in the preservation of the relics and restrain the damage caused by animals.
　　3.Separate the preservation area and the visiting zone;insulate the possible harm caused by human activities and contamination;and accommodate the requirements of different types of relics.
　　4. Create a new method of relic preservation and serve as the example,guidance and reference for future projects.

汉阳陵·比萨：文化遗产的原址保护与考古博物馆