To authenticate Chinese antique jades from the scientific aspect,從科學層面鑒定古玉

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  1. Proper identification of ancient jade artifacts from China should employ both subjective (expert opinion) and objective (scientific) lines of evidence.  The latter is often minimized by appraisers and authenticators, or excluded altogether from jade identification.Dr. Daphne Rosenzweig, a world-renowned expert in jade identification, stated that systematic analysis of the jade itself should be used to determine authenticity, not simply to understand its origin or whether it was owned by a prominent person.  Similarly, Mr. Yang Boda, an ancient jade master, believes that if research and appraisal are based solely on expert opinion, then important clues regarding jade authenticity may be missed.  He advocated a better way to research and identify ancient jade artifacts.The better way advocated by Dr. Rosenzweig and Mr. Boda was to place more importance on the scientific investigation of ancient jade artifacts, and less importance on the opinions of often ill-informed authorities.  Even excavation reports, thought by many to be the quintessential authority on jade authenticity, may be misleading.  For example, the unearthing of jade artifacts from the tomb of The Lady Hao (Shang Dynasty, 1600-1052 BC) produced a jade phoenix from the Shijiahe Culture (2500-2000 BC) and jade hooks from the Hongshan Culture (4700-2900 BC).  It is quite possible that all three types were excavated from a single location but at different depths representing different time periods. The first layer may have belonged to the Shang Dynasty but the lower layers likely produced the artifacts from the Shijiahe and Hongshan cultures.   When identifying ancient jade artifacts, all factors must be considered objectively, and in detail, so as not to make the mistakes made by less-informed authorities.

    Scientific examination of jade artifacts should include the following physical and chemical properties of jade “weathering” (or aging) over time:

    1. Differential weathering – Depending on the nature of long-term exposure to soil pH, sunlight, and water, one side of an artifact may show a greater degree of aging than the other side.
    2. Diffusive markings – Exposure of jade surfaces to the elements may create natural staining that blends, or diffuses, into the jade rather than appearing as a blotch on the surface with relatively sharp margins.
    3. Dissolved pits – When jade is buried in the ground, particularly in the presence of water, the surface may be exposed to different chemicals (including acids) that over time form irregular holes on the surface. These pits allow staining and erosion to penetrate farther into the interior of the jade, producing different shades or gradations of color.
    4. Exposed crystal planes – Exposed crystals are crystals transformed from the jade itself due to physical factors such as heat and pressure. They are sometimes called micas. Almost all the antique jades buried underground have shown evidence of exposed crystals.
    5. Amorphous silicates –  Nephrite is a gem-quality silicate mineral in the Tremolite–Actinolite series of amphiboles. When nephrite is exposed to weathering in soil, the outer portion of the jade surface can be dissolved and then redeposited on the surface in another form: amorphous silicates.  A mineral is in an amorphous phase when it maintains its chemical composition but has lost its shape and crystal form. It is often seen in the burial jades as whitish greyish paste-like (but highly durable) sheets of minerals on the jade surface.  This whitish bloom is often mistakenly referred to as calcification.  Water is the primary medium and the main driving force for chemical weathering of this type.
    6. Secondary growth crystals – Similar to amorphous silicates but representing a later stage of development is the formation of secondary growth crystals. Secondary growth crystals are crystals added to the jade artifacts from exterior sources, including Hematite (reddish iron-oxide crystals) and Tremolite (black, needle-like crystals; a principal component of Nephrite), among many others.  In the case of Tremolite, needle-like flat crystals are fabricated into the jade surface as new material. These crystals are raised above the jade plane and scatter from the center in different directions. The distribution of the additive crystals can appear as plaques (thickened plates) or with a more regular, often dendritic, form.

    Through his long and illustrious career in research, Mr. Yang Boda firmly established the use of scientific methods in the identification of ancient jade artifacts.  His founding ideas and school are irreplaceable.  Mr. Yang’s scientific view of jade appreciation is rich in meaning; his philosophy may be summarized in the following manner:

    1. The study of ancient jade has grown from a functional level to embrace a range of scientific disciplines, including mineralogy, geology, gemology, technology, materials science, and other aspects of scientific investigation.
    2. The study of ancient jade should be combined with archaeology.  Artifacts from different historical periods have different artistic styles; while different artifacts from the same historical period often have similar artistic styles. Moreover, because excavated cultural relics may be broken, the jade excavated with them may play the role of a standard instrument by which to identify the ancient culture. Therefore, the ancient jade dynasty can be proved from archaeological materials and the jade to postulate the age of other excavated cultural relics.
    3. The study of ancient jade should incorporate an understanding of historical jade literature. Chinese jade culture has a long history that has been recorded in ancient documents of successive dynasties.  While it is not advisable to accept this record without some degree of scrutiny, the insights afforded are invaluable.  With the correct attitude to study and examine historical documents, we can find relevant evidence for ancient jade connoisseurship and achieve the purpose of resolving doubts.
    4. The study of Chinese jade culture should also expound on its external characteristics and essence owing to its place in theology, aesthetics, ethics, and philosophy. Chinese people have revered jade and jade artifacts since ancient times, to a degree not found anywhere else in the world.  Jade worship pushed to the extreme the idea that jade was the food of spirits and gods of heaven and earth.  Jade was therefore used in god sacrifice and as a theosophical deity.  The respect of jade over time has been exemplified by jade sacrifice, moralizing jade, advertising it as the embodiment of a gentleman, and standardizing the ideological cultivation and behavior of politicians and literati doctors with the virtues of jade. ( note: the English description is edited by Dr. Mark D. Schaaf Science Program Director| Air Sciences Inc.)

    古玉的鑒定是客觀而科學的. 一般而言, 古玉可透過觀察玉器本身是否具備下列物理化學特性加以測定:差異風化,顏色,溶蝕孔(玉器埋在在地下時, 表面若接觸到不同的化學物質, 所形成之不規則孔洞, 一般是洞口小擴散沁色(玉器表面受到不同礦物隨著玉之紋理結構, 侵蝕滲透至玉器內部, 所形成深淺層次不同的, 洞內大且有角礫岩), 晶體曝露(曝露晶面是古玉受外界礦物影響所形成低於玉器表面的反光體(又稱雲母片)) ,次生長晶體(次生結晶體是古玉受外界礦物影響所形成高於玉器表面凸起的物體(多為針狀)且與古玉表面平行,這些針狀晶體系覆蓋於刀工紋飾之上,說明了玉器雕琢在先,次生結晶體的形成在後. ).159226637377637639

    世界知名的玉器鑑定專家 Daphne Rosenzweig博士認為, 要針對玉器本身作有系統的分析來從事鑒定, 而不是看此玉器的出身或曾為那個重要人士所擁有.
    古玉泰斗楊伯達認為古玉研究和鑑定如果只是建立在經驗的基礎上,是不會有多大作為的,他要為中國古玉的研究和鑑定找出一條新路來。
    最重要的是, 直接判斷玉器本身,而非”先入為主”的訴諸權威看法. 有時候, 即使是出土報告的結果都未必可信. 例如,婦好墓除了商代玉器, 還出土了紅山文化的玉勾形器及石家河文化的玉鳳,也有可能在同一位置, 不同深淺的出土, 屬於不同時期的遺物. 例如, 第一層屬於商文化, 第二層屬於龍山文化. 所以在同一地方可能出現兩個時代以上的玉器, 也就不足為奇了.因此在鑑定時,每種可能的因素都要客觀的詳159226646156436608細的加以考慮, 才不會犯假權威常犯的錯. 
    楊伯達先生經過長期深入的研究,將中國古玉鑒定建立在科學基礎之上,其開宗立派的歷史作用是無可取代的。楊先生的科學賞玉觀內涵豐富,其方法論概括如下:
    1.研究古玉不能僅僅停留在它的功用層面上,還要從其礦物學、地質學、寶石學、工藝學、材料學等方面進行研究  
    2.古玉研究要同考古學結合。不同歷史時期的器物具有不同的藝術風格;而同一歷史時期的不同器物在藝術風格上往往有相通之處。更由於出土文物可以進行明確的斷代,其相伴出土的玉器在古玉鑒定上可以發揮標準器的作用。因此,古玉斷代可以從考古材料中找證明,從出土文物中類比年代。
    3.古玉研究要重視文獻的考證。中國玉文化歷史悠久,歷朝歷代的古文獻都有記載,當然對這種記載不加分析全盤接受的觀點不可取,但是也不能對這種記載缺乏信任而不去學習體會其含義。以正確的態度研究考證歷史文獻,可以為古玉鑑賞尋找出相關證據,達到解疑釋惑的目的

    4.研究中國玉文化還要從神學、美學、倫理學、哲學諸方面闡述其外在特點和內涵精髓。中國人自古以來就崇玉、尚玉,這是世界上其他民族所沒有的。崇玉推至極致就認為玉是天地鬼神的食物,於是玉被作為祭神、通神的神物;尚玉的最高境界是比德於玉,將玉道德化,標榜為君子的化身,以玉的美德規範政治家和文人士大夫的思想修養和行為。