Results 1 to 2 of 2

Thread: Chroming/Chromium on Qin Bronze swords

  1. #1
    Join Date
    Sep 2004
    New Zealand

    Chroming/Chromium on Qin Bronze swords

    Conclusions follow in the second post, but for the purposes of a thorough account I include the following........

    I posed a question on the reliability of claims about chromium plating on the Qin buried army swords to a Yahoo group on artifact studies.
    These ‘chromed’ swords are often mentioned in texts, or the internet,, as well as other exotic compounds being used like titanium & magnesium in the bronze claimed on occasion too.
    I put this to since I had never heard much elaboration on the supposed ‘highly advanced anti-corrosion technology’ and I had in the past found some specific claims made about these swords to be false.
    Some of the replies make the issue far from conclusive, but do indicate there is enough reason to suspend judgment before repeating the chromium surface-coating idea as established fact and neither should the effects be claimed as preserving the swords like new.
    Both Jim Connell & Richard Nable are broadly experienced with ancient bronze weapons, and Lluís Mendieta is an academically trained chemist.
    The discussion should be of benefit to those that may want to understand a little more beyond the exaggeration that is more typical.

    Just consider about the chrome coating on stainless Qin swords, that if you hear somebody say it three times that is not enough in itself to make it the truth.
    The ‘chroming’ that occurred was neither effective as it has been claimed, not is it ‘chroming’ in the modern sense. It seems there is a process there, but the reporting of it is incorrect to compare it to modern methods or even imply a layer of chromium exists. It may be that there is 0.6% to 2% chromium in the outer layer of the swords but it was neither isolated as an element or applied with the great effectiveness as is claimed.

    My conclusion follows a presentation of the information I could gather.

    \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\\
    Kenneth wrote;
    "For the groups attention I should add that while looking at pictures I was again reminded of the, just a little dubious, claim of chromium on the surfaces of Qin swords.
    This is often mentioned to explain the perfect preservation of the swords, but is at best a half truth since several show corrosion of a typical nature and a normal ‘red-copper’ looking surface. …..
    …..My question is for the geologists and metallurgists especially.
    How credible is the claim of anti corrosion surface treatment technology at 0.6-2% bronze alloy?
    & could this be a natural impurity from the copper?
    Geological in origin?
    Other accounts call the mystery ingredients ‘titanium & magnesium’…..
    …… Is there really something special about these swords & truly unknown on other Chinese bronzes or is this just a little bit of hype and journalism rather than science.
    Certainly the appearance of the Qin swords is not unique, and comparable to many well preserved bronze blades of the same period, especially a high tin % bronze.
    On CHF I wrote;
    ……”it is worth adding an observation that some pictures I see of the Qin swords show quite typical corrosion on the surfaces (patina), and even one sword broken in half, despite the more commonly shown glossy and perfect looking specimens.
    The anti-corrosion treatment, chromium, claimed for the swords does not in fact seem to have prevented some from developing a mineral patina in a fashion much like other Qin weapons or another Eastern Zhou bronze, some are shiny and others have corrosion.
    This is another subject (anti-corrosion technology) that in some circles been questioned despite being told almost any time the swords are mentioned in books or the media, i.e on swords with less than 1% chromium (examples range from 0.6-2%) such a proportion is not effective in modern understanding of chroming.
    Percentages in less the 1% are actually in the range of natural impurities that occur from bronze casting due to the sourced copper ore and this is also another potentially blasphemous but valid topic that could merit discussion."

    \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \
    Lluís Mendieta wrote;

    Dear Kenneth/List
    Well, the blades are just wonderful. And the work of a master.
    But for corrossion/cromium/titanium/magnesium content in that bronze.
    Going for what is easy and going to more complicated

    If any of this blades show magnesium in metal state, it is a modern fake. Not magnesium as an impurity, occluded inside the bronze cast as, say, magnesium silicate, that could be used in the maing of the mould.
    But magnesium metal, its solely presence means fake, and modern magnesium bronze.
    Reasons: magnesium is prepared as metal by electrolysis. In those times, there is no technology, so no pure metal could be done.
    The other way, reaction with ferrosilicon of the double oxide of magnesium and calcium, would require a technology also that they have not (prepare ferrosilicon and also the temperatures)

    Well, I doubt also that any of those blades could have titanium. If there is titanium as free metal, then it is a forgery.
    Titanium is produced by the Kroll process (and that needs magnesium...So, we are at the end of the road)
    If the ores are processed with carbon, as reductor, then you get the refractary titanium carbides...

    Well, it is produced by electrolysis in electroplating. No technology available in that period of time
    Or it is produced by reduction of ore processed to get the chromium oxide, that is further reduced by aluminium or silicon.
    Not having aluminium neither silicon, they could not have chromium.

    So, the mere presence of those free metals should imply a forgery by a not so knowledgeable forger.
    If any ore containing those metals in the state of any salt, oxide or that were used, they would not produce the metal in the conditions in which the copper would be done, and less in the conditions of bronze producing.

    -For corrosion, or lack of it.....:
    Corrossion of bronze pieces depends mainly in the environment where they were preserved.
    If dry, not submitted to fires, in a not too polluted area, they could withstand a lot.
    Is like the iron Asoka column: not stainless steel; just iron and few precipitations and dry environement.
    I have seen some Dian objects that are fairly well preserved.
    I own a Tang cash coin that is altered to cuprite (submitted to a high fire is an sealed big container that permitted to create and recrystallizate the cuprite, but not permitted to be further corroded by water...). Found in Xinjiang, perhaps in a very dry area.....
    With best wishes
    \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\\\\\\\\\\\\\

    Kenneth wrote;
    Hi Lluís,
    Thanks for the info.
    The swords are certainly not fake. Quite a bit of nonsense is said about them though, either from invention or hearsay. It seems many textbooks have unfortunately reported this hearsay and this is why I am curious about how the proffesional studies (I assume some studies actually did occur) deduced all the mystery ingredients.
    One paper on the Chinese bronze age which was quite detailed then matter-of-factly mentioned titanium and magnesium in the bronze alloy too. Now I expected a professional standard for proffesional publications, so I checked the original source.
    A geology paper. Who I am to doubt?.....(beyond just being inherently suspicious).
    Here was the passage from a paper by a person named Cowen and posted by an educational institution.
    This source paper is a dead end though, not further references for this statement.

    ...."The Chinese became more sophisticated bronze metallurgists than their Western counterparts. The famous terracotta army of the Emperor Qin, made for him about 220 BC and buried with him, have weapons that are basically bronze, but they have been deliberately alloyed with metals such as titanium, magnesium, cobalt, and so on, no doubt after empirical trial and error, to give superior hardness and penetrating power."

    Titanium, magnesium, cobalt, and so on? It didn't even mention the better known chromium, like everyone else. Just what are the real facts?
    I actually tend to believe there may not even be any real facts.
    At present I consider the claims about unique anti-corrosion technology using these substances are unproven, to put it mildly.
    It may be, as I have found in the past, such 'facts' may date from a headline in Xinhua (the Chinese media) whose journalists have inaccurately reported archaeological discoveries on other occasions. When a reporter makes a story, and paraphrases a real expert on the very well-preserved nature of certain swords I can just see this pattern of behaviour. 'Chromed appearance' as a tin-oxide layer may have become 'Chromium' in the same way any pre-Shang site (even found in Mongolia) can become 'Xia dynasty city found'.

    Now if I follow correctly Chromium naturally occuring is rare, and it is industrially made from chromite by a process using aluminium and silicon, neither which occur naturally for this process either. The temperatures required of 2,000 °C to extract alluminium from ore sound in excess of even the remarkable temperatures of Chinese blast furnaces of the period which allowed them to cast iron over 1,000 years before Westerners.

    Chromium is mined as chromite (FeCr2O4) ore. .....Though native chromium deposits are rare, some native chromium metal has been discovered.

    .....Chromium is obtained commercially by heating the ore in the presence of aluminium or silicon


    Richard Nable wrote;
    I have had the opportunity to examine a large number
    of Chinese bronzes with the silvery coating that seems
    to be corrosion resistant. In every single case we
    find the normal elements of bronze with a
    preponderance of tin and silicon on the surface. The
    surface colors are often varied but the elements are
    fairly consistent. Even on pattern etched pieces the
    results are the same. I have not yet found any nickel
    on any of the pieces examined.
    ….. Most pieces are only analyzed on the surface through
    electron microscopy but on a few random pieces I have
    done cross-sections or drilled samples to have "wet"
    analysis confirm the findings. So far, no surprises -
    though I must admit I had hoped for some.

    Lluís Mendieta wrote;
    Dear Kenneth/List

    Newspapers sometimes make "curious" translations of what is said, being moderate.
    Recently {it} was said in a newspapers that an important collection of chinese cash-coins was donated to a USA university by a professor of such university, that {he} was chemist, and that "have confirmed the {in}geniusness of the coins by chemical analysis"
    When I asked, a member of the staff of such university {named} in the group {said} that the Professor authenticated the coins by style, *not* by analysis!

    …..After this digression, I think again that you are right in what could have been said and what has been written...
    {C}oins, in China, some black shiny patina is called black mercury, red mercury and the green mercury.
    Needless to say that not one of those patinas have any trace of mercury....
    Then, if you do not know, a translation could be that those patinas have mercury. And the hearsay begins to move.....

    I personally was {taught} by my professors in chemistry that all should fit, and that the {simplest} explanation {tends} to be the real {explanation}...(Occam's Razor)
    \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\\

    Richard Nable wrote;

    I have read some of the work on the "chromium" plating
    on ancient weapons. I have also discussed this indepth with the metallurgists at the lab.

    The only work that we can find supporting the chromium
    theory was done in the early 1970's and that single
    analysis has been cited in every other work I have
    been able to locate in English language. The original
    analysis reported something like 3% chromium in the
    plating on some bronze which, according to everyone I
    have talked to, would have little effect (if any) on
    the appearance of the bronze and would not affect
    corrosion resistance. If anyone has any first-hand
    references to any analyses done to support the
    chromium claim, I would be very interested in seeing
    them. I think it is more likely that any chromium
    present on a bronze was an accident (present in a
    paint applied to the surface or leeched in from the
    surrounding soil) or the result of something else
    unrelated to advanced plating technology. I have had
    the opportunity to study many objects with the silvery
    coating on them and all of them so far have been tin
    and silicon.
    \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\\\\\\\\\
    In March 2007 Gordon Couger wrote;

    I was watching a show on TV that found Chrome on
    the surface of weapons
    from ancient China.
    I doubt that Chromium was refined in the modern way. Finding how it was
    done should be interesting.

    Gordon Couger
    \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\
    {extract from documentary
    ”On a visit to China, Branwen Morgan visited the terracotta warriors and was intrigued to find that some of the ancient weapons appeared to be chrome plated….
    ….Besides copper and tin, the bronze weapons also contain nickel, lead, magnesium and chrome. Mr Zhang Tao, a museologist at the Museum of Terracotta Warriors notes that the swords have been heat-treated and are chromium plated. Indeed there is a very fine 10 – 15 micron rust proof chromium oxide coating on the swords and this consists of .6 – 2% chromium. Incredibly, chromium plating was not used in the West until the 1900s, although chromium was discovered in Paris in 1797.

    So, is it possible that chrome plating was being used to prevent rusting in China during the Qin Dynasty? Frank Walsh, a professor of electrochemical engineering at the University of Bath in the UK, believes it is unlikely. Conventional plating techniques require the objects to be dipped in a chromic acid bath. He told me that “it was more likely that chromium was present in the metal mix”.
    Historical records show that during the peasant uprising at the end of the Qin Dynasty, 206BC, parts of the mausoleum were plundered and fires that lasted for 90 days were lit. Unfortunately, many of the wooden pits containing the terracotta warriors were burnt and many of the artefacts were found covered in ash. Professor Walsh notes that the heat from the fires and the presence of carbon would have provided a reducing environment in which chromium atoms could have migrated to the surface of the weapons. There they’d oxidise and form a protective coating. This would explain the heat treatment that Mr Tao noted. Metals do diffuse over time, so this ‘natural’ explanation is plausible….….So, although it’s unlikely that the Qin Dynasty can lay claim to the technique of chrome plating, the unprecedented magnificence of the entombed terracotta army, horses and bronze chariots and the legacy of the Great Wall will be marvelled at for centuries to come.”

    Jim Connell wrote;
    The press release below trumpets this 'discovery' but there is
    not one respected journal article I can find that gives credence
    to the discovery or presents any data from the study in question.

    To me the use of the analytical techniques said to have been
    used in this study would have resolved the issue.
    The absence of the publication of the data itself leads me totally
    disregard the hype.
    "In mid March 2005, archaeologists and metallurgists
    examining bronze swords forged during the Qin dynasty (221-209 BCE) reported evidence that
    the swords had been chrome
    plated. Using electron micro-analysis and laser technology,
    scientists from the China
    Research Institute of Nonferrous Metals and the Chinese
    Academy of Geological Sciences,
    in an effort to determine why some bronze swords unearthed
    from the burial pits attached
    to the mausoleum of Qin Shihuang were not rusted or
    corroded, discovered that they were
    coated with an extremely thin layer (10-15 microns) of
    chromate and dichromate
    compounds. This chrome plating, which gives bronze a greyish sheen, strengthened
    swords and preserved their sharpness, while also preventing
    corrosion and rust.
    The technology seems to have been lost with the spread of iron
    weaponry, and chrome plating
    was only re-discovered by German scientists in the early-20th
    century and patented in the
    \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\\\
    {…note they say ‘forged’, not cast as is all bronze, suggesting a few issues with reporting. They also claim a ‘chrome layer 10-15 microns thick, a tiny fraction of a millimeter, somehow strengthened
    swords and preserved their sharpness which is simply nonsense.}

    Lluís Mendieta wrote;

    To soak a bronze blade in cromate solution is not chrome plating. That is feasible technology in the time of the blade, and could be completely real……..

    To make sodium chromate is relatively easy:
    Take chromite, an ore that could be available to the Chinese in those times. Not specially abundant, but found.
    Melt with soda ash during a long time, letting oxidize by atmospheric oxegen and you will get sodium chromate.
    Treat the residue with water and you will have a solution of sodium chromate.
    {extracted from link;
    It is not normally necessary to make chromium in the laboratory as it is so readily available commercially. The most useful source of chromium commercially is the ore chromite, FeCr2O4. Oxidation of this ore by air in molten alkali gives sodium chromate, Na2CrO4 in which the chromium is in the +6 oxidation state. This is converted to the Cr(III) oxide Cr2O3 by extraction into water, precipitation, and reduction with carbon. The oxide is then further reduced with aluminium or silicon to form chromium metal.
    Cr2O3 + 2Al → 2Cr + Al2O3
    2Cr2O3 + 3Si → 4Cr + 3SiO2}
    \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\\\\\\\
    But, then it comes the hearsay again
    -Yes a film of copper chromate could protect the bronze from further oxidation (I doubt, but is possible). But copper chromate would be dark olive. No make an special effect of colour, could be....But not especially appealing, unless the master blacksmith would to highlight the white of the tin rich bronze of the letter in front of the dark blade....
    -But no, it would not increase the hardness of bronze, nor make it sharper....
    Hope that that serves...

    With best wishes
    Lluís Mendieta
    \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\\\\\\\\\\\\\\\
    Tripitaka: 'You should live without fear. There's as much chance of good things as bad things.'
    Sandy: 'It's a cheerful philosophy and I've heard it from people before. They're all dead now though.' (1:4) .

    "The strange fact is that the world goes on against all reasonable odd. A hundred years, and even unimaginable evil is just called history."

  2. #2
    Join Date
    Sep 2004
    New Zealand
    I found a surprising bit of detailed information in Yang Hong’s; ‘Weapons in Ancient China’ at the beginning of the Western Zhou section it mentioned more on the swords.

    Investigation of one of the Qin dynasty bronze swords that are still rust free revealed that it was coating with a thin layer of air-tight oxide found by electric probe to contain 2% Chromium {the oxide layer rather than the bronze presumably. Note another text says the % found vary from 0.6-2%.}
    Proton X-ray fluorescent examination again confirmed the existence of chromium on the surface of the sword.
    According to the analysis made the sword had most probably been immersed in molten potassium chromate or boiled in a soloution of potassium chromate. Chromate or hypochromate salt can be prepared by heating chromium ore with saltpeter and dissolving the end product in water, heating to about 800-1000 degrees-celsius.
    {the same treatment allegedly applied to the bronze arrowheads, said to keep them stainless after over 2,000 years}.””

    This is the most detailed account yet. Many texts don’t mention the actual methods, or fail to mention the surface treatment at all (one Chinese text just called it ‘possible evidence for surface treatment shown by testing).

    The source for this in Yang Hong was a 1978 publication from the ‘Beijing institute of iron and steel technology’ which I expect it what Richard meant by the only paper he has seen referenced. The only other source Yang Hong gives for swords is later discussing general topics a ‘preliminary report’ of excavations from 1975.

    Potassium chromate is created using pure chromium (K2CrO4). Chromite (ore) does exist in China, although it is not noted as a supplier in the world industrial scale. It could be mined in China if ancient alchemists recognised it and made Potassium chromate from it.
    The major chromite resources of China occur in ophiolites and continental intrusions. Podiform chromite deposits are mainly developed in the Palaeozoic and Mesozoic ophiolitic mantle sequences. They occur as tabular, lenticular, or irregular masses hosted by dunite lithologies, or dunite lenses, or harzburgite associated with dunite lenses. Main stratiform deposits occur within the Archean Northern China craton and are named as the Gaosi-type deposits, which are contained in intrusions similar to their Alaskan-type counterparts and are characterised by their ring-shaped ores.

    I am unsure if X-ray fluorescent examination, as given as the testing method by Yang Hong, is based on personal interpretation of data, such as flame colour testing of compounds by visual judgement, or if this result is based on machine computation of results. In 1970’s PRC this would be very unlikely to be a computerised scanning. A drilled powder sample might be more conclusive and confirmation of the results through a tiny destructive sample in modern times. Several methods from surface testing, drilled samples and scanning electron microscopy should be used to confirm results.
    The 2005 study Jim referenced apparently found chromium too when ‘some’ of the uncorroded swords were tested by electron micro-analysis and laser technology yet the reporting of this was notable for errors of fact and no original publication of results is cited or availible. Testing of corroded swords too would have been a good idea as a control sample. I assume this accounts for the lower % results of ‘chromate’.

    Whether the results are correct it still would not be true to call the arrowheads, or swords, stainless.
    Most Qin arrowheads are quite normal in appearance with visible corrosion products like any other moderately patinated bronze.
    The swords also exhibit mineral patina on several examples, although typically only the best preserved are even shown in discussion so as to emphasis the ‘unique’ effects of ancient technology.
    I had seen some of the swords in person and do not recall any surface appearance that would have made me think they had a truly unique appearance for ancient bronze.
    As an example here are a few pictures that suggest limitations to some of the claims made about Qin sword characteristics.

    Normal appearance shown, glossy, but take note of the broken blade.
    The swords are very high in tin% (around 20%) which makes for a sharp edge but a less durable blade. Stories of the springing of long bent blades into shape when pulled from the soil owe more to ‘Crouching Tiger Hidden Dragon’ than reality.
    The sharpness of the swords is also often declared, but there is nothing, even the supposed ‘chroming’ that would make them sharper than usual. Bronze swords can feel as sharp as kitchen knives are 2,500 years as I have experienced this but MR. Wang at Shaanxi museum told me they are not ‘sharp enough to shave with’ as people claim, since ‘he had tried’.
    The stories about cutting stacks of paper, also said of the Goujian sword, are very un-scientific sort of measures and also likely just myth woven around the swords.

    More typical appearance of well preserved bronze swords, green patina is visible here. Depending on burial conditions quite ordinary swords can have no patina at all, so the visibility of green malachite on the surface here shows corrosion products on the surface.
    Another sword, a different one based on the location of the break, shows a fractured blade.
    Ordinary bronze swords of the East Zhou can have damage from burial, being under pressure from the weight of earth or collapsing soil. It suggests again the swords have more normal properties. Certainly they lacked the ‘spring’ or flexibility some stories have given them.

    Heavy corrosion products, scabbard remains. The scabbard here will be like iron and bronze swords I have seen where fragments of the wooden scabbard are held by corrosion products, mineral patina. These can be converted into, or are simply bonded by, malachite or other minerals that form on bronze over long periods of time.

    There are few firm conclusions to be made about the Qin swords.
    Given the attention to uniformity in Qin weapon production the measured 0.6% to 2% of chromium alleged in some texts is hard to understand. Nor is the effect of this anti-corrosion treatment really as effective as it is supposed to be. Some people even doubt the material was deliberately added to the surface.
    It seems clear the swords are not ‘chromed’ in the sense we understand it today, nor was the identified material used to coat them chromium as such, but a reduction of chromium in combination with other material (into Potassium chromate) and it may be that chromium was created in a reduction process rather than actual isolated.
    To show this little distinction about ‘chroming’& ‘chromium’ in a meaningful way…
    This is Potassium chromate

    This is Chromium

    Actually applying pure chromium to the surface of another metal was still beyond people until modern times.

    The Qin technology then seems less mysterious, since modern plating of chromium uses electrolytic deposition (i.e electricity) and true ‘chroming’ is still a recently discovered process.
    The idea of ‘lost & super advanced’ techniques from over 2,000 years ago is put in a little perspective. When stripped of the typical misrepresentations in reporting it still shows that Chinese bronze casters must have experimented through trial and error to produce certain effects in their product. There is inventiveness, and remarkable ingenuity be used here, as in other masterful ancient weapons from the same period, yet the normal account I see are not comparing apples with apples.
    The ancient ways are not comparible, or the same, to modern techniques. This is where the exaggeration and misrepresentation of the actual ‘chroming’ needs a little sober reflection.

    Given the benefit of the doubt, saying the potassium chromate process existed as per Yang Hong, the surface treatment was neither applied consistently/evenly to each sword and nor was it truly successful in keeping the weapons as stainless as is claimed.
    Tripitaka: 'You should live without fear. There's as much chance of good things as bad things.'
    Sandy: 'It's a cheerful philosophy and I've heard it from people before. They're all dead now though.' (1:4) .

    "The strange fact is that the world goes on against all reasonable odd. A hundred years, and even unimaginable evil is just called history."


Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts