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Scientific analysis of the Leichhardt nameplate
Paper presented by David Hallam, Senior Conservator, National Museum of Australia
Leichhardt symposium, National Museum of Australia, 15 June 2007
MATTHEW HIGGINS: I would now like to introduce David Hallam, who is a senior conservator with the Museum. David was the driving force behind that 12-month scientific analysis of the nameplate. The marriage of the scientific analysis and the historical record that resulted from the last 12 months of activity on this was quite fantastic. David, I’m looking forward to hearing about your revelations from what science can tell us about the nameplate.
DAVID HALLAM: One of the most fascinating things is that eventually Leichhardt got to Perth, but it wasn’t quite in the way that he expected to. He was flown to Perth in an aircraft and stuck into a vacuum chamber attached to a scanning electron microscope. That’s what I’m going to talk about. The question I was asked was: is it ‘real’? It’s a seemingly simple question. In most cases it’s impossible to prove an object’s authenticity, but the process we undertake at the National Museum allows us to make a balance of probability assessment.
Looking deeper, the question we had to answer was: was the plate made before 1848 or was it a later fabrication? Again, it sounds simple, but you can’t just carbon date metal or put it into a machine that tells you it was made in 1835. What you can do is look at the technology of production, the methods of fabrication, the evidence of the environment it’s been in, and the evidence of the stress it’s been under. Together, these will prove verifiable, causal links to the object’s provenance; in other words, links to the story that we get from [Reginald] Bristow-Smith. They will show these links are non-existent or they will show that these links are real. If they exist, the story is real and we can tell it truthfully.
One of the things we need to think of is objects in a museum. Most modern museums have made a shift away from the way we look at object authenticity. We have moved away from representing objects as having defined identities towards saying, ‘This is the object; this is what we think we know about it; please use this information and make your own assessment of what you think about it.’
One of the best ways of getting information out of objects is to look at them really closely. We can look at the surface; we can look at them stylistically; we can look at things like patina and corrosion products; and we can look at usage. The techniques that I used were my eyes, an optical microscope, and then we also looked at them under a scanning electron microscope.
The plate is made of brass and has letters stamped into the front of it – LUDWIG LEICHHARDT. Then at one end it has some numbers made up of stamped and engraved numbers - 1848. On the back it has some cuts, it has strikethrough where someone has hit the stamps hard enough to bend the metal and distort it. It’s got black corrosion product. It’s got a copper overlay on the surface, strange one. It’s got a bit missing of the copper overlay round the pinhole. It’s got file marks on the surface. The style of the lettering is consistent with early 1800s. You can see how the ‘4’ is made up of a composite of ‘I’s and bits of other letters. You can see again the file marks going across the surface. The file marks have happened after the stamping was done, because when you stamp a piece of metal you distort the edge around the stamp mark, and you can see all of the file marks have happened after that.
The cuts on the back are very similar to the kinds of cuts we sometimes find on Aboriginal breastplates. I have no explanation for that. The letters would have been made basically on an anvil using an engineer’s letter punches. Here you can also see the copper overlay on the surface. These are the engraving tools that would have been used to make the ‘8’s. The person who did the engraving was definitely not a skilled engraver, because they had several goes at doing the ‘8’s and got them wrong several times. If we have a look at the letters we find that the letter ‘A’ is filled in, which I’ll discuss later.
If we carry on looking we can start to look at things like the corrosion products that we find in the various areas of the plate. We’ve got zinc-rich areas and sulphide corrosion. If we then start to look at some of the chemical analysis, we have several methods we can use for chemical analysis of something like the plate. Obviously you could grind it up, do a macro-analysis on it and end up with no plate. You could do an analysis that used a very small amount of the object. You could do analysis that is destructive or analysis that is non-destructive. For this kind of operation we always aim to do things that are totally non-destructive to the object. In this case we had to use what’s called an environmental scanning electron microscope, which exists at CSIRO [Commonwealth Scientific and Industrial Research Organisation] in Perth.
We have also used X-ray fluorescence and Raman microscopy for analysis, which I’ll talk about later. We are considering doing some laser ablative mass spectrometry, some neutron activation and some metallurgical replication analysis on the plate, but that has not yet happened. If we look at the X-ray fluorescence data we come through with copper percentages about 60, zinc about 35 and lead about 0.4. In other areas you’ll have copper percentages about 76, zinc about 18; copper about 65, zinc about 31; copper 75. You’ll see that the surface of the plate is actually very variable.
Our X-ray fluorescence data complemented the data we got under the scanning electron microscope, which is far more accurate than our X-ray fluorescence data. Here we come through with an average zinc composition of about 36 per cent, and an average lead composition of about 1.5 per cent, with no tin. We have metals from dated sources as a comparison. One of the things we are currently doing is going through looking at the brass breastplates that are dated in the National Museum’s collection, comparing them with this data, and we are finding a very good correlation.
What do we know about copper, zinc and brass production in the nineteenth century? We know that early on in order to make brass you got some copper, you heated it up with zinc oxide and that produced a brass that had a maximum percentage of zinc of about 32 per cent. Normally it was around 20. It wasn’t until 1832 that [George] Muntz patented a method of mixing together copper and zinc metal to get a brass with a much higher zinc concentration. This was mainly used for things like ships’ hull cladding. So this is something that would have been quite available in Australia.
From looking at the metal composition we can say that the Leichhardt plate was made from a combination of copper and zinc metal. We also believe, but I have yet to prove this, that a British zinc was used. From about 1880 onwards copper was electrolytically refined, so we would end up with lower levels of impurities than we have in the Leichhardt plate.
If we have a close look at the surface we can see some of the scratching file marks on the surface. When you look at it really close up, we’re going up to 400 times the size and you can start to see the lead crystals. You can also see that the surface of the metal has dissolved with little marks in the surface and an amazing amount of detritus in the scratch marks which could be analysed and looked at. You can see the dissolution pores all over the surface. That shows that it’s been in a corrosive environment.
Let us move onto the corrosion profile. Things that we look at here are the dezincification. If you have brass and you put it in a corrosive environment, the zinc goes into solution and that is called dezincification. When the zinc goes into solution the copper goes into solution with it and then is redeposited onto the surface and plates out. That’s why the Leichhardt plate has a coating of copper on the surface. It’s fairly even, it’s not very well adhered but it’s there.
We also found the presence of sulphur and chloride in the corrosion products. In a close-up of an area you can see one of the letters, the copper over plating and the base brass metal. If we look at an analysis of the brass you can see copper, zinc and chlorine. If we look at the copper analysis you can see copper and a whole potpourri of corrosion products - little bits of aluminium, magnesium, carbon, oxygen, and on it goes. If we take another look, we see our sulphur coming through in our corrosion product, and again you’ll see aluminium, silicone, magnesium. If we take another look we will see copper, zinc, chloride, sulphur and if you look at the copper overlayer you’ll see just copper coming through, which shows redeposited copper.
When we look in the letters one of the things which really threw us was that we found titanium. When you’re looking at doing an authentication study on a work of art, as soon as you see titanium you say, ‘post 1930s’. We found titanium and we thought, ‘What form is it in?’ We did Raman microscopy and we found it was titanium dioxide, a pigment - oh, dear. Then we found a photograph of the plate on display in the South Australian Museum with white pigment in the lettering, which is what we can see. That was taken in 1935 when titanium would have been quite available. We also found amorphus carbon in the lettering, which leads us to believe that there was a resin in the lettering and that it was exposed to a low temperature fire in a reducing environment, and basically what was produced in the lettering was the equivalent of carbon black.
These were the conclusions of our analysis. A lot of the data you get visually under a scanning electron microscope is very hard to quantify. When Dr Ian MacLeod first saw this nameplate he said, ‘It looks real.’ The finding of the lead under the scanning electron microscope was the clinching piece, because modern brasses from about 1850 onward do not have that composition of lead in them. The sulphur – where would you get sulphur from? If it was Rotorua, that would be fine. But where in the natural environment would you get sulphur from? If it had been in an anaerobic environment buried in a peat bog then you’d get sulphur, but where else? There is only one source, and that’s black powder.
Chloride, where would you get that from? Well it was on a horse, it was with a sweaty person, but also the nitrates in black powder from that period had very high chloride concentrations. Black powder was incredibly corrosive. The zinc hydroxychlorides were the clinching thing for the arid environment. They only exist and are only produced in an arid environment.
The presence of the other elements - the potassium, the aluminium and the silicone - are just the kind of thing you’d expect from someone rubbing an object with ash from a fire. The Raman testing found colloidal carbon, and it is highly likely that this indicates a low temperature fire. We can analyse the colloidal carbon by laser ablative analysis, but that’s semi-destructive so that’s going to be an interesting one.
The physical evidence that it’s been bent to me was also very telling. If something is held onto a stock with a pin and you’re just trying to remove it, how are you going to do it without bending it? There’s also evidence on the plate that it has then been straightened out again. You can see hammer marks on the back that are post corrosion. We speculate that the brass was re-formed from another object, because on the back we can see an ‘O’ and the cuts in it. When you look at the structure of it it’s not a very nice piece of metal; it’s a beaten old piece of metal. It’s not terribly consistent. That leads us to wonder, and this is only speculation, whether it was made in a blacksmith’s shop on the Darling Downs in a hurry just before Leichhardt was about to go - it’s quite possible.
One of the important things to remember is that an object’s story does not cease after it enters a museum collection. Acquisition gives museums access to the primary source material - and this object is definitely primary source material. It enables the Museum to undertake research that few individuals have the resources to undertake.
I would like to acknowledge the following people for their assistance with the investigations: Dr Ian MacLeod of the Western Australian Museum, Ms Lau from CSIRO, Professor Creagh of the University of Canberra, Andrew Viduka at MTQ [Museum of Tropical Queensland] and my colleagues at the National Museum of Australia. Thank you.
MATTHEW HIGGINS: Thank you very much, David. When David took the plate to Perth for these studies at the CSIRO with Dr Ian MacLeod, we all waited with bated breath. Would we get the smoking gun - no pun intended - would we get that piece of evidence which would show that it was an early nineteenth century piece of brass? I’ll never forget the rather excited phone call that I received one afternoon at my desk from David in Perth saying, ‘There’s lead in it,’ which proved that the brass was from the right period and that it wasn’t a later piece of brass that had been fabricated.
PETER STANLEY: I’m not an expert in anything that’s being discussed this morning, so I’m thinking: what is my role? My role is as a devil’s advocate to ask questions that might help to illuminate the truth. What you’ve said is very interesting, but the plate is reported to have been attached to the stock of a weapon, a musket I suppose. Do we know of any other muskets that have brass plates like this with names attached? Was this a common thing? Is there physical evidence that would support the attribution of its origin?
DAVID HALLAM: In the Australian War Memorial’s collection there are plates on rifles from the late 1880s and 1890s. On some of the Boer War stuff, people wrote their names and beautifully engraved things. So, yes, it was a habit of people to put their names on weapons.
PETER STANLEY: And whereabouts, on the base of the stock or on the side?
DAVID HALLAM: I don’t think that this could be on the base of the stock, this would have to be on the side of the stock. It would also have to be inlaid into the surface of the wood, and you can see that there’s been an attempt to do that. The final filing of the plate was done when it was in something. To have it only held by one pin, it would have to be inlaid and glued maybe with an animal glue. There is a precedent for that, and I think there’s a precedent for Leichhardt for naming his stuff too.
MATTHEW HIGGINS: Yes. If I could just add that there is evidence that Leichhardt was very methodical with his gear and quite possibly had a numbering and lettering system for the equipment that he took with him. We also know through Darrell Lewis’s research that there was chap in Victoria called Bennett, whose descendant lives here in Canberra and whom we met recently. Bennett provided a pair of pistols to Leichhardt which were engraved with ‘from RB to LL’. They have never been found, but Bennett wrote about this in the Victorian press in the 1880s. So there is another precedent for someone having given firearms in this case with an engraving – that’s presumably engraved into the metal and not a separate plate. That is further supporting the evidence for the fact that someone either gave him this firearm or at least the plate to mark his passage through that part of the country.
DARRELL LEWIS: Just to comment on where the plate was on the gun: my father was an antique gun collector and I’ve seen hundreds and hundreds of guns of all vintages. Just about every gun I’ve ever seen has had a specially made and shaped plate to go on the end of the stock to prevent the wood from splitting if you bang it on the ground, and it was curved to fit your shoulder and so forth. There is no way that plate was on the end of the butt; it was on the side somewhere.
DICK KIMBER: I have no particular expertise but I found the presentation fascinating for the detail. I think I’m right in saying that Charles Harding who owned it originally used to often have it wrapped up in a bit of cloth. As a bushman you’re going to use grease of various kinds and if you’re going to show the gun to someone almost certainly you’re going to lick your finger and rub it a bit and you’re going to have people rubbing the butt with different things. I wondered if there might also be some oil on a rag that you’d use as a preservative? That’s only a speculative possibility.
DAVID HALLAM: There’s a lot of rubbish in the letters, and that’s the best way I can describe it. Those letters are almost a micro-archaeological excavation waiting to happen. There’s an immense amount of information still hidden in the object. There could be pollen in there, remnants of peoples’ sweat - all kinds of things, because it’s many layered. You’ve got the carbon layer but then you’ve got the titanium whites, and under that I’m sure there’s another layer of calcium oxides and things like that. In those letters themselves there’d be quite an amount of investigation we can do to find gosh knows what.
DAVE UNDERWOOD: I was rather surprised at the size of the nameplate; it is rather large, I thought. You were talking about the ones over at the War Memorial, what size are they? Is that culturally the size for that era? I was also going to ask you about one hole rather than two.
DAVID HALLAM: That would quite easily fit onto the butt of a rifle.
DAVE UNDERWOOD: No, I’m saying for that time.
DAVID HALLAM: Yes, about that size.
DAVE UNDERWOOD: It’s pretty big. In this day and age they’re much smaller, aren’t they?
DAVID HALLAM: I think the size of it was governed by the size of the lettering they had. My impression is that whoever did this only had one set of lettering, and that was the size it had to be to fit on.
DAVE UNDERWOOD: I have another question, if I may: any speculation as to whether it was hanging up in a branch or inside the boab tree? Do we have any ideas about that?
MATTHEW HIGGINS: We don’t. We can only speculate upon that. Whether it was left as a deliberate marker in the landscape - this is where we were, we are dying, this is our memorial because it’ll be found above the ground and be more easily seen. They’re the logical things that spring to mind, but we can only speculate until we find further evidence.
PHILIP JONES: There’s been only a fleeting reference to the gun. I wondered whether people were aware of the attribution by JB Cleland in 1938 to the possibility of it being Gilbert’s gun. In a letter to Dr George Bennett of Sydney in September 1847 Leichhardt mentioned the possibility of using Gilbert’s gun which had come into his possession. I just wondered whether you knew any more about this and what sort of a gun it was?
MATTHEW HIGGINS: I’m assuming you mean Gilbert as in the first expedition, who died on the western side of Cape York?
PHILIP JONES: Yes, and apparently Leichhardt had received this gun from Gilbert’s widow.
DAVID HALLAM: We don’t have any information on that. Darrell, do you have a comment to make on that?
DARRELL LEWIS: There is absolutely no information about what kind of gun it was. It was just a partly burnt and rusted gun. We don’t even know if it was in a bottle tree, leaning against it or stuck into it by force. We have that little bit of information that it was found in a bottle tree. Undoubtedly the expedition had more than one gun anyway, each man would have had a gun of some sort you’d think. One account has it that Leichhardt was allowed to pick police carbines for all his members. I am not sure if that was for the first expedition or the second, but the chances are if it was the first he would still have them for the second anyway. So until someone finds the remains of a gun near a boab tree marked with an ‘L’, we won’t know what it is.
MATTHEW HIGGINS: Thank you, Philip, for raising that suggestion.
PHILIP JONES: Just to follow up on that: we know it is Leichhardt’s gun that this is from and we know that the gun was actually collected and was in the possession of Charles Harding and was subsequently thrown away, which seems to be rather odd. Surely you would keep the metal parts of the gun as a relic as sacred as the plate itself? It strikes me as odd.
DAVID HALLAM: I don’t think if you were on the edge of the desert you would bother to carry a dead, out-of-date, rusted gun. You’d just leave it there; you wouldn’t carry any more weight than you had to. One of the things you must remember is that this gun would by then have been definitely old technology. It would have been about as useful as a Hewlett Packard calculator is nowadays. What do you with a Hewlett Packard? You pick it up and you throw it in the bin or you sell it on eBay, you certainly wouldn’t cart it half way across the world.
PHILIP JONES: If it has Ludwig Leichhardt’s name on it, I think you would.
MATTHEW HIGGINS: It is an interesting question, Phillip, and we have wondered about that too. This story raises a lot of questions, and we have been able to get answers to a pleasing number of them. Darrell Lewis and I have talked about where the firearm might be. We know that it was not only rusted but also burnt, so obviously would be in a very deteriorated condition. We presume that [Harding] discarded it for that reason but kept the plate because he recognised that as the greatest thing of value.
David, thank you very much for a great presentation.
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Date published: 14 March 2008