It is only recently, because of recent controlled archaeological digs of the last few decades, using modern scientific dating techniques (such as radio-decay and thermoluminescence), that it has become clear that jade working in China extends back over a long period prior to the Shang era. In fact, Chinese archaic jades of the Bronze Age and later are the product of a long development process, extending so far back through the Neolithic period (to about 5500 B.C.) that the period of jade working before the Shang era now appears to be longer than what used to be considered the classic period of archaic jades, the Shang to Western Han.
In fact, many Chinese jade experts now consider the very peak of
archaic jade work to have been reached in the Neolithic period, in the
magnificent jades of the Liangzhu culture, in particular their stunning
two-register congs, of which Angus Forsyth writes (in
[Forsyth]): "There is a
fearsome, cold reality .. about the high precision detail and volumetric
organization of the two register congs which sets them far apart from, and
above, all other neolithic jades." (In the opinion of this author, and many
others, he need not have limited himself with the qualifier "neolithic".)
One unusual aspect of neolithic jades is that regional differences are far more pronounced in neolithic jades than later jades. Indeed, most jades dating from the dynastic period (Shang through Han) show very little regional differentiation, although some has been noticed, e.g. between the kingdoms of the Warring States period. The regional differences in neolithic jades are not only in form and ornament, but also (uniquely to the neolithic period as far as this author knows) in technique as well.
As pointed out in [Keverne], this provides a very valuable diagnostic tool to anyone examing neolithic jades. Technical details of how holes were bored, how cutting edges were sharpened, et cetera will often indicate with near certainty (as much as one will get with pieces where the provenience is not known) which culture produced a given archaic jade piece.
One thing that must be taken into consideration, in considering this regional technical differentiation, is that the working of hard-stones (by techniques other than flaking), for functional items such as axes, was widespread in neolithic China, and the working of jade appears to have grown out of this earlier work. Many of the earliest neolithic jades replicate functional hard-stone forms, in particular axes, and indeed some early jade axes appear to have been functional pieces (based on evidence such as wear and chipping along edges).
Thus the regional differentiation in jade-working techniques may be
nothing more than a recapitulation, in jade techniques, of prior regional
differentiation in stone-working techniques, although it does appear that
regional technical differentiation increased over time in jade-working, as
further regional technical advances in jade-working changed jade-working
techniques even within a given cultural region.
For blades, the term "face" refers to one of the two large surfaces of
the blade, "side" refers to the two non-sharpened side edges of the blade,
"butt" refers to the non-sharpened back edge of the blade, "edge" refers to
the cutting edge of the blade, and "facet" refers to one of the two opposed
surfaces of the cutting edge.
Probably the single most valuable technical diagnostic is the manner in which holes were made. A number of different aspects are involved: which technique was used to make the hole; whether the hole was bored exclusively from one side of the material, or both; whether the finished hole was polished inside, or left raw; what shape hole resulted (in longitudial cross-section), straight-sided, conical, et cetera.
The earliest hole-production technique is "pecking", in which small amounts of material were removed by repetitive blows; this technique appears to have been used only on hard-stones, as jade's resistance to fracture probably make this technique impossible to use on jade.
In late working, two techniques seem to have predominated for making holes: solid- and hollow-boring. In the former, a solid rod with the end coated in abrasive material (perhaps quartz sand in a grease matrix) was rotated, and eventually wore a hole through the piece. In the latter, a hollow rod (perhaps a piece of bamboo) was used instead, and a cylindrical piece of jade was "punched out". The former technique seems to have been the earliest, and been less common later on, but it seems to have lived on for the production of small-diameter holes. Perhaps the latter technique was preferred later on as, since less material had to be removed (particularly for larger holes).
In holes which are bored from both sides, if the resulted hole was
not polished internally, it is usually possible to tell, from the traces left
where the holes from each side met, which technique was used. Hollow-boring
resulted in a small ridge where the two holes met, with the sides of the ridge
meeting at a fairly obtuse angle. Solid-boring, with the resulting
dome-shaped hole, results in a more prominent meeting-ridge (and thus a
smaller through-hole, relative to the size of the hole at the surface of the
material), where the two sides meet at a fairly acute angle.
The Hongshan and related cultures seem to have all used small
two-sided solid-bored holes, ones in which the bore almost always meandered
in passing through the material.
The Dawenkou culture seems to have generally used two-sided solid-bored holes, although there is some variation in this.
Of the thirteen blades or blade-like objects with holes from the Dawenkou site shown in clear cross-section ([Dawenkou] pp. 36-37, 44), eleven have two-sided holes. Of these, with two exceptions (117:8 and 110:3), they all either i) have steeply conical sides (more typical of solid-bored than hollow-bored holes; although at least three of these, 9:32, 122:9 and 69:2, show evidence of pecking as well as boring), or ii) were obviously solid-bored (12:6, 112:3, etc).
Of the two exceptions to the above, 117:8 was bored from only one side, but shows signs of pecking on the side which is not bored, and 110:3 seems to have had the hole polished after boring. There are the two single sided blades (70:1 and 25:9).
Of the nine blades with holes from the Yedian site shown in clear
cross-section
([Yedian] pp. 34-35),
all nine are clearly two-sided, all have
steeply conical sides (more typical of solid- bored than hollow-bored holes),
and at least two (M49:5 and M62:48) were obviously solid-bored. None show
any signs of pecking,
The later Longshan culture is characterized by single-sided hollow-bored holes, absolutely conical, and polished to a fine finish inside.
The Liangzhu culture used two-sided hollow-bored holes for larger
holes, and two-sided solid-bored very conical holes for smaller holes. It
may also have used two-sided solid-bored holes for larger holes at an early
stage, during the Songze-Liangzhu transition, but this is not certain.
Another key technical indicator is the way in which blade cutting edges are formed.
Some edges are perfectly straight, and others gently curved. Another
differentiation is what the edges look like in longitudinal cross-section
(i.e. from the edge to butt): some have flat facets, and form a relatively
thin blade, whereas others have more convex facets that form a more
full-bodied edge.
The Dawenkou and Logshan cultures used a techique of hollow-ground edges which results in edges which are perfectly straight, and a gently curved back line where the edge facet transitions into the blade face. Along with the absolutely conical single-sided holes, and very flat and highly polished faces, these make Longshan blades absolutely distinctive in all Chinese archaic jade work.
The Liangzhu and predecessor cultures have blades with curved edges,
and the facets of the edge are convex curves which blend into the blade body
with no noticeable transition line.
It is not clear exactly why these regional differences in technique exist, and indeed we may never know for sure, but we can posit a number of hypotheses.
One possibility is that jade working appeared completely independently in different areas, each with a dissimilar, and indigenously developed, set of jade-working techniques. This would require that populations in each area independently decided to focus on jade as a medium of art, which is not impossible (the South American civilizations seem to have focused on gold as a medium independently from the Euro-Asian civilizations, as it seems unlikely that the neolithic peoples who colonized the Americas had any familiarity with gold at the time they came over).
However, given the emerging evidence of wider trade patterns among neolithic peoples (based on chemical and isotope studies of raw material sources) than previously imagined, perhaps such a level of isolation was not the case in neolthic China. That leads us to other possibilities, the second being that finished objects were either seen or traded outside the original region of jade-working, which led to local production of jade objects. With just the concept of jade objects, and without knowledge of actual techniques, each region would have independently discovered jade-working techniques, leading to regional differentiation.
The final possibility is that basic working techniques were spread by some process (either contact or diffusion of jade-working populations), and once the basic techniques had spread, local technical differentiation appeared as local workers gained familiarity with the medium, and independently attempted greater technical facility in working with it.
Whether any way exists to distinguish among these hypotheses, using archaeological evidence, is an intiguing point; the author cannot think of any. In any case, perhaps all three mechanisms did operate, at various times and in various places.
It seems clear that in later periods, as communication improved, jade
workers throughout China concentrated on a single set of the best techniques,
and regional techical variations disappeared. Thus, the history of stone-
and jade-working techniques in archaic China may in the end be a cyclic one,
in which a basic idea spread out uniformly, underwent regional development,
and then coalesced back into a uniform xxxx.
[Dawenkou] "Excavation Reports of Neolithic Tombs at Dawenkou" Wenwu Press, Beijing, 1974
[Forsyth] Angus Forsyth, Brian McElney, "Jades from China", Museum of East Asian Art, Bath, 1994
[Huang] Xuanpei Huang, "Gems of the Liangzhu Culture: From the Shanghai Museum", Hong Kong Museum of History, Hong Kong, 1992
[Keverne] Roger Keverne, editor, "Jade", Van Nostrand Reinhold, New Work, 1991
[Yedian] "Zouxian Yedian: A Neolithic Site", Cultural Relics Publishing House, Beijing, 1985