DOFF Cleaning comes from outside our niche, but has become a valuable too in bronze conservation.
Today, I talk to Brian Crowe of Stonehealth. Brian and I became acquainted when Antique Bronze began to look around for a wider range of conservation tools that could serve us.
Initially, we were a bit wary of air-powered tools. Back in the 1990’s, we had seen the popularity of blasting/peening grip the metal restoration industry, but time after time, we saw war memorials and sculptures which had been cleaned back to bright metal and in so doing leaving a mattish, unmetal-finished surface which resulted in sculptures that looked very different to their previous selves.
Unsure about the results we witnessed, we decided to stick with traditional hand-preparation techniques when dealing with corrosion treatments. Hand-prep techniques had their critics too, but we had more faith in the method particularly as it was so controllable.
To our minds, the oomph that machinery provided seemed to be at the expense of a bronze’s surface.
However, there were certainly times, particularly when we had very large projects, when we felt the need of a power-assisted tool. This was when we came across Brian Crowe, and his DOFF cleaning and JOS/TORC tools. Unlike regular air-abrasion, JOS was something a bit different, firstly it was wet abrasion, rather than dry, and it was designed to clean more softly, be controllable and less aggressive.
Today, you can Listen (or read this transcription) to Brian who tells us in his own words, the history of what and why Brian brought his conservation tools to market.
Lucy: Brian, you and I have worked together for a long time. We’ve bought your products over many years and your wonderful tools. And so I’m very pleased to have the opportunity to chat to you today, not just because you’re such a nice chap, but also because it will be nice to be able to talk about some of the things that you have developed at Stonehealth, which I think are a big contribution to the conservation tools that we have for large objects.
I know that you probably sell mostly to the stone markets, stone conservation and restoration. But, we’re particularly interested in metals and large-scale metals particularly and, actually, we’re quite limited with our tools in this field, for a number of reasons because, obviously, we’re mostly onsite and so that’s why I appreciate the work that you do because it helps my job be a little bit easier very often. I know your background very well, but just for other people LISTENING in (or reading!), just tell us a little bit about how you started the company and your background?
Brian: Okay. Well, thank you for those very nice comments. First of all, Lucy. You made my head feel a bit bigger than it should be.
Lucy: Not so.
Brian: But, going back into the 1980s, I came to a particular point in my career where I’d been working for very large companies and also one or two smaller companies, mainly in the toy and the textile field. And I thought I wanted to do something on my own. I’d made one particular company become a very strong company just through some product developments. So, I decided I’d break out on my own. But, I wasn’t quite sure what market to get into. But I did find that there was a company in Germany that was working with some consolidants for stone, and that became quite interesting and I was talking to English Heritage about that and John Ashurst, in particular, was very interested in what that did.
In the meantime, another company approached me, which said, they had this machine for cleaning stone and it didn’t do any damage. So, I went over to Nuremberg to the stone fair to see what was going on. And I was quite impressed by it. So, I decided to arrange for some of ours in the UK for the system which we called JOS, Yoss, as the Germans pronounce it. So, I set up a demonstration in London, Bristol, Birmingham, and Edinburgh and the results were very startling and it impressed me a lot. But, what we found was that the contractors were saying,
“This will be a new thing. Here today, gone tomorrow. We’ll buy one if we need one.”
But it was the specifiers, the architects, in particular, who were showing some interest.
And I remember one of our first projects was a building called Saint John’s, right opposite Waterloo station. And, obviously, you have the old choo-choo smoke all over the building that’s 100 years old. The architect asked the contractor to carry out some trials, which included the Jos. When he came to look at it, the contractor said, “Well, that one is a bit too slow.” And, “I don’t like that. I don’t like that, but that one I do like.” And he said, “How much slower would it be?” And he said, well it would take another couple of weeks.
And this was quite impressive. The architect said, “I couldn’t care less if it takes another year. This building has been around for a few hundred years. It should be around for a few hundred more just for the sake for you to get off-site.” So, he specified it and, in fact, the job didn’t take any longer than using any other method, but it was done in a very responsible way. And strangely enough, that architect, or coincidently I should say, the architect was also responsible for St James’s Palace. So that was the next project that took place.
Brian: In the meantime, the cathedrals became interested. And so Lincoln, Salisbury and Canterbury, as well as Westminster Abbey were starting to use it. So, it really did become a big thing. It wasn’t one of those things where it’s here today, gone tomorrow.
Lucy: As the contractor predicted, badly.
Brian: Sure, now I’ve been involved for 33 years, and though it was not really taken that seriously in the beginning, after that first three years when we realized we had some future, we formed Stonehealth Ltd and then started expanding away with this.
But we found a problem with the company that supplied us, and it was at the time when the wall came down in ’89. That’s Germany suffered a bit of a setback and the company that developed the JOS went down, unfortunately. I think it was partly due to a rags to rags in three generations where a grandfather who was a Dr. of chemistry, he started the company. His son took over, who was also very diligent and hardworking and then the grandson took over, and he was really only interested in things which were fast and that was cars, boats, and women.
Lucy: Expensive hobbies.
Brian: Well, it’s not the sort of attitude or type of person you want to run a company. So, suddenly left with being without the supplier of the most important project or the product that we had.
Lucy: Huge setback.
Brian: It was a big setback and very concerning, but one or two other companies in Germany that were supplying that particular company, approached us direct and we decided also to get some local supply. And so we got it up and going. Before this happened, the original JOS nozzle did have a problem of, unfortunately, wearing out pretty quickly. And it was quite an expensive item. So, together with the Germans, developed a way of making it modular so it could be…the wearing parts could be replaced, which made it a lot more economical and that’s where we then called it the TORC.
Lucy: Oh, I see.
Brian: So, that was a big step forward. The first time the TORC was being used was on the British Museum around the old library when it was covered over. And the contractors who were using it said,
“We’re finding that this is using less material and it’s a gentler clean, and it’s working quicker.”
So that was a big improvement over the JOS nozzle and so that was a big step forward.
In the meantime, people were finding problems in removing paints. Now, sometimes the Jos and then the TORC would remove paints such as limewash and also carbon, of course, but it wouldn’t remove the more modern paints, which were flexible. So, in talking with a friend, who I met through the business, a Dutch person, he said, “Brian, if we can get temperatures up to 30 degrees, I’m sure that’s going to destroy a lot of paints. So, the next thing is we’re looking at a system, which was developed for cleaning industrial machines, etc., and it was working at 150 degrees.” And we said to them, “Will it remove paint?” “Don’t know. Let us give it a try.” And it did. Paint just sort of came off very quickly…..in a very impressive way. So, we worked with that company for a bit until they were taken over. Then they went a different way. In the meantime, we developed the systems ourselves and we manufacture those now totally here in the UK. So, the TORC and DOFF cleaning, between the two of them, will remove most unwanted matter. I’d say 90% either one after the other or all together. And the results are good without doing damage.
Lucy: I’ve got to say, one of the things we really like for the TORC or is it Jos/ TORC…I’m probably pronouncing it wrong “Jos.” It should be YOSS…
Brian: It’s okay. Really, you’re English.
Lucy: One of the things we’ve found is that we use it quite often on removing limescale on fountain bronze because bronzes in fountains, although they look magnificent with the waters cascading over them, it’s often when the water supply is turned off and on periodically, that you get a lot of limescale developing and hardening because what happens is it starts to bake in the sun.
And although the limescale deposit isn’t always reacting necessarily with the bronze, it’s relatively inert, it does really claw into the cast surface of the sculpture. And so Gosh, it’s hard to get off and we don’t want to use any chemicals because…particularly acidic chemicals for limescale because if it goes through that limescale layer and it gets to the patina underneath, it will strip that patina. Actually, we’ve found it really, really good for being able to, in quite a controlled way, thin out those limescale layers because, obviously, you’re using quite similar aggregates, aren’t you?
Brian: Mm-hmm, yeah.
Lucy: So…. I know that…the aggregates differs depending on if you want it coarser or thinner…finer. But we’ve had quite a lot of success with that. It’s useful for corrosion removal as well, but certainly, limescales are really one of those ones that very few tools will deal with very well. There’s all sorts of difficulties with limescale.
Brian: Yes, I can understan that. And I mean, obviously, in hard water areas, that’s likely to build up even quicker and as you say, it calcifies. And that becomes really hard. And what’s nice about the TORC is that it buffs away. It’s like wearing it away in a controlled way unlike grit blasting where the grit goes directly at the surface in a quite an aggressive way, this rotates on the surface and it buffs it away. And you can remove those calcium deposits and come down to, what I understand you want, is the bronze to look like a dirty penny and to leave that patinary in place.
Lucy: Well, it certainly depends on what the original finish was. Quite often, fountain statuary is quite diverse in its intentional finish or in the finish that has adapted. It’s just that lovely aspect of having the control there. To be able to stop and investigate, you know, where are we? What have we got here? Is this, this point we want to stop? Whereas, obviously, if you have another tool which just sweeps it all away, you haven’t got that thinking and transition period, really.
Brian: Yes. What’s the important thing is, as you say, you’re able to take away what you want to take away and leave what you want to remain or retain. I remember sort of layers and layers of old paints. And it was like taking one layer off and then the next layer off. And it was like steps. You could see the history of this particular piece of stone and what paints had been put on it over a period of time. And that just shows what sort of control you’ve got. And I…
Lucy: Well, that’s… one of those kind of things that a conservator dreams of, you know, to be able to have ultimate control.
but whilst we may be able to provide good systems and products, it very much comes down to the person behind that machine
or that product who applies it. You know…
Brian: You know, you can give a good car to a good driver and they’ll drive even better. But, if an idiot is behind the wheel, a good car goes up and down curbs and knocks down lampposts, etc., you can’t blame the manufacturer. That’s why there’s so much emphasis on the training of operatives. I know it applies more to stone and masonry, in general but that’s the reason why we’ve now adopted this system of having an approval system with the rosette, which does at least give specifiers some form of assurance that, at least, hopefully, they will get a better job done.
Lucy: Well, absolutely, and I think the thing is that anyone with an ounce of common sense knows that that’s the case with all treatments, especially on historic objects. We’ve learned that from the past, haven’t we, with all the disasters that have happened? If you have somebody with experience and knowledge, then they aren’t going to be gung-ho with a technique that they’re not familiar with. It’s not within their scope – which is not the kind of ethics and principles that we try to uphold in conservation, obviously.
But I don’t think you can level that criticism just at, you know, your own tool. I think damage can be done by … well, lemon juice can damage bronze very severely. Coca-Cola and, I mean, no one thinks to be trained in drinking Coca-Cola, but the damage I’ve seen done by it is quite extensive. So, yeah.
Brian: Just shows how carefully one has to be.
Lucy: Absolutely. But tell us a little bit about the business model, Brian, because I’m quite interested in conservation companies. And I know that yours is…it’s, I think, a company that thinks quite a lot about the way it operates not only with its staff but generally. It’s quite an ethical company. And I kind of like that because I remember, a long time ago, somebody saying to me, “Oh, don’t you think there’s a kind of disconnect between making a living and also being an ethical company?” And I don’t agree with that, and I argued the case, but let’s hear what you say.
Brian: Well, good for you in arguing that because I mean there are a lot of people that just think that a company is there to make money and to do so at any cost. No, I’ve always found, from experience, that if you look after a customer well, they become a loyal customer. And sometimes even if you’ve got a discontented customer, if you put them right…tell them what’s wrong, they become an even much more loyal customer. And you used that word, “ethical,” and that’s a very important matter to us because we try to take a responsible way with, not only with the commercial side of the business but also the responsibility for making sure that people do the job properly.
I’ve had people who have said to me, “Can I buy so and so,” and then I found out what it’s for and I’ve said, “No, it’s not appropriate for that.” And they say, “We’ll still buy it.” And I say, “Well, no, I’m not prepared to sell it to you on that basis.” And so, there are people who would say, “Well, you know, you’ve sold it, so what does it matter?” And I remember one of the companies who was making some chemicals for us in Holland was taken over and the person who was running the business, he showed us how certain things worked and one of them didn’t go that well. He said, “Well, it doesn’t really matter as long as you’ve sold it.” I was disgusted with that sort of approach because, you know, you want to build up a good reputation, not only with your customers but with your staff as well.
And I always remember, back in my days with textiles, one of our large customers in the UK. This was an Italian company, but one of the large customers in the UK was John Lewis. And going to their offices, there was a notice up to say that, “Sir, we regard our suppliers as important to us as our customers. So, if there’s anything wrong, please let us know.” And I think that’s quite a challenging thing to put over to people because there are times, as I say, “When you don’t sell something, you don’t want to sell it to them because it’s not appropriate.” But they come back because they know you’re taking a responsible approach. And if you do say that is the product for doing something, then they’re more likely to listen to you rather than being sold to. That’s something that I’ve always felt. As a company, we prefer people to buy from us, rather than us selling to them.
Lucy: That’s definitely a very personal relationship you’re building then because they’re able to trust you. I think that, even though, in your case particularly, it’s being done for the best intentions, I also think it’s a good business strategy anyway.
If people can rely on you, they’re going to feel that you’re not going to lead them in the wrong direction.
And in the long run, that’s got to be better for them as them using the products. How does it benefit anybody to have that short-term thinking? I can’t see it myself.
Brian: Well, I think, you know, there’s been situations and examples of companies that have actually taken that more aggressive approach and they haven’t lasted that long.
Lucy: Yeah, for sure. So, you’ve also diversified though, haven’t you, because you have many products as well. I’m always interested to have a look at new products coming out in the market, and you’ve got quite a range now.
Brian: Sure. In fact, as I said earlier, 90% of the unwanted matter can be removed either with the JOS or by DOFF cleaning, either separately, or together. And there’s another 10% where one does need to revert to other methods such as chemicals. Again, we try to take the ethical, responsible, approach in products which are safe for the environment, the person, and anything else that…and the building itself.
So, you don’t want to do any harm. So, we try to do that. We’ve got a company, a local company in Holland, that produces some very good conservation tools under our own specification. They seem to work very well such as for the removal, in your case on metals, to get rid of the oxidation and on bronze, etc., and also moulds as well. Also salt is a big problem so we have poultices for poulticing out salts.
Lucy: Absolutely. We do like the Cuprid which, I know, is the poultice that we use to remove the copper staining that you get, particularly on plinths. And, obviously, on statuary that isn’t being maintained, which always should be, but often isn’t. And so then, not only is the statue degrading obviously, but the impact on the plinth or the surrounding stone on a building is incredibly negative visibly anyway.
Brian: Particularly when it’s just been cleaned. If you’ve got some carbon or some other soiling, and you remove that, let’s say on Portland stone, and all of a sudden everything looks green then…
Lucy: Everyone is shocked.
Brian: …And then even with the Cuprid, you know, you may need to use two or three different applications because sometimes that gets way down into the surface.
Lucy: Oh, yeah. Absolutely. But there’s no magic bullet with anything, is there?
Lucy: As far as I’ve come across, you can’t treat everything in one hit?
Brian: No. And it’s all trial and error. You know, we say to people, “You know, it may be the answer to your question, but try a small area in an inconspicuous place to see if you get the results you need before going on to doing something which is staring you in the face.”
Lucy: So, you must be doing quite a lot of development work at Stonehealth because…I mean, we’ve all got to eat, so we’ve always got to deal with current projects that are on the docket. But there also seems to be quite a lot of forward-thinking in what you’re doing?
Brian: I think that’s necessary.
I always think that a company needs to move forward in order to stand still.
That sounds a bit funny but there’s always a natural wastage and a moving on. You know, customers come and go, and you need to find new customers and new products as well to actually just standstill.
Brian: So, yes we do both on the mechanical side. I mean, we’ve got an interesting new development going on at this moment. It’s being held up by some sort of technical hitch, but we had hoped to launch it back in July, but it probably won’t come out till next year now because we do want to make absolutely sure that it is going to work properly and reliably before it’s put on the market.
Lucy: How interesting.
Brian: …Because we don’t want people to feel let down.
Lucy: Well, no. I mean, I suppose though there’ll be some beta testing, first, I would imagine, getting feedback from people who…without marketing it properly?
Lucy: You know, with that kind of thing. I think that’s always great advice. I always try to…even though it’s always a hard thing to ask, “what did you find wrong with it?”
Lucy: Sometimes the answers are not as you’d like them to be, but on the other hand, if you just, you know, swallow the pill, you can often actually advance quite a lot from that.
Brian: I agree.
Lucy: Yes. Well, Brian, it’s been lovely talking to you. I know that we use the DOFF nearly every day with our treatments. A lot of our bronze work, it’s the initial stage nearly always, particularly for restoration projects. And our DOFF cleaning machine has been a real workhorse. It really does a lot of hours so, you know, it’s sort of a friend – definitely one of the team.
Brian: That’s great, Lucy.
Lucy: So, you know, we’ve been really pleased with it, but thank you for taking the trouble. I should say that Brian has been a very good sport because he has had to record this interview a second time owing to my inability to manage to capture it the first time. I had a tech gremlin interfere with the interview, so I thank you in particular, Brian, for having the patience to do it again.
Brian: My pleasure. We got there in the end, Lucy. That was nice.
Lucy: We did.
Find out more about the tools at Stonehealth – take a look at their stunning website – Stonehealth
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Cleaning of this iconic War Memorial and restoration was necessary after white gloss paint was thrown over The Bomber Command War Memorial in Green Park earlier this year.
Conservation work by Antique Bronze took place some weeks later after the memorial was initially hit.
The monument is a magnificent creation by sculptor, Philip Jackson, who won the Marsh Award in Public Sculpture for his work. It’s easy to see why: the artist has personified bravery, comradeship and patriotism in the stance of his figures, their detail and expressions. We enjoyed many conversations with the public who came to visit the memorial during our works.
Why This War Memorial Is Special
Several of the visitors had interesting facts to tell us about the Bomber Command unit which was instrumental in winning World War II. Of the 125k men who served, half lost their lives. Bomber command crews came from 60 different countries. Every member was a volunteer. The average age of those killed was 23 years old.
Hours after the monument was vandalised, an emergency clean was undertaken. It was then that the RAF Benevolent Fund was advised that a monument cleaning service specialising in conservation should take on the due to complexities of working on bronze.
Removing the remnants of white paint from the bronze’s surface was not an easy task. Although much of the paint had been taken off in the initial clean, thousands of smaller splashes remained.
The surface of the sculpture had originally been hot patinated, but areas were fragile. Before the treatment was started, we noted that there was evidence of localised loss of original patina. This meant that to avoid further loss of the surface, the cleaning technique decided upon had to be very gentle indeed.
The aim of bronze conservation is always to leave as much of the original patina intact as possible.
Another difficulty was that the surface was highly detailed meaning that many of the tiny splashes were located deep inside small grooves making them hard to excavate.
It may seem like superheated water or high-pressure cleaning may be an obvious option for this type of vandalism, but the fragility of the patina made this route a concern. The paint was so firmly adhered to the textured surface that to shift it, force would have to be centred on a very tiny surface area which had the potential to break-up more of the original patina.
Solvent cleaning was useful for softening the deposits, and soft nylon brushes did clean the surface without damaging the patina, but this cautious route on such a large monument made it a slow task. Our most useful tool came in an unexpected form – small wooden coffee stirrers provided the perfect profile to clean out grooves, but was soft enough not to scratch the patina.
War Memorial Cleaning Tips for Custodians
If your memorial has been vandalised, consider these three tips:
- Never use sticky tape to cover the surface – even if the graffiti is offensive. Industrial tapes contain residues in their adhesive which will etch through a bronze’s patina often causing more damage than the paint layer itself.
- Call a professional monument cleaning service (like us!) for advice and help – if you try to use high-pressure cleaning methods on bronze, and you have a vulnerable surface, you can instigate serious loss of the original finish.
- Don’t ignore vandalised bronze – it invites further anti-social behaviour.
Restoration of the masterful statue of Sigmund Freud by Croatian Sculptor, Oscar Nemon, was recently undertaken by Antique Bronze.
The Tavistock Clinic have a fascinating art collection which this monument is a part of. In Mind, The Tavistock and Portman Foundation staff magazine, wrote a feature about the works, text reproduced here:
Freud Gets A Makeover
Outdoor statues in London have a tough time of it: the vicissitudes of the weather, the pollution, the pigeons… So it is no surprise that the bronze sculpture of Freud outside the Tavistock and Portman NHS Foundation Trust, which was partly responsible for introducing Freud’s psychoanalytic theories to British medicine, is receiving much-needed restoration work.
Led by Lucy Branch, Senior conservator at Antique Bronze, the statue restoration team started work on Monday 5 July by giving the sculpture and its plinth a steam clean. Then they began the careful restoration work by hand, using fine copper brushes and pumice powder to remove corrosion. As Lucy, who has a degree in fine art, did a three year apprenticeship and a masters in post at the V&A, explained: “Corrosion forms unevenly in patterns so they need to be blended out by hand – you want the sculpture to be seen as the artist intended and not have your eye drawn to areas of degradation.”
The statue restoration is made more difficult by the hot weather. With the full sun on the sculpture it gets very hot causing the cleaning materials to melt and evaporate. The public have also been very interested in what is going on and Lucy says:
“It is important to be able to engage with people, while getting on with the work, but we have had quite a few rude comments.”
The sculpture is by the Croatian artist, Oscar Nemon, who grew up in Osijek on the borders of the Austro-Hungarian empire. He studied in Vienna in the 1920s, which is where he first developed an interest in the work of Freud. He then moved to Brussels, becoming a well-known portrait sculptor. In 1931 he received the commission to sculpt Freud for his 75th birthday. Freud was a little uncertain, but agreed to let Nemon sketch him in brief sessions between one patient and the next.
Overnight Nemon produced a preliminary clay and that won Freud over. Nemon continued to work for several years visiting Freud whenever he passed through Vienna on his way to Osijek and then finally in London in 1938, after the political situation had led both men to leave mainland Europe.
It is these London sittings that led to the final harsher, more abstract sculpture in terracotta which were used for the bronze sculpture that now resides outside the Tavistock Centre.
On seeing the sculpture Freud commented in his diary:
“The head, which the gaunt, goatee-bearded artist has fashioned from the dirt — like the good Lord — is very good and an astonishingly life-like impression of me.”
Lucy Branch is similarly appreciative of the work saying: “When you get close to the sculpture it is really beautiful, with clearly defined tool marks on the surface. Freud is seated in a very dominant pose, making this a powerful sculptural figure, but also a fine representation of a man drawn from life.”
The restoration of the statue will be completed with more colouring work. Then layers of protective coating will be added, to make the statue as stable as an outdoor statue can be.
Find the whole article here: Freud Gets A Makeover
If you’d like to know more about restoration work on bronze, read a case study on our blog, or if you want to be taught about the principles of bronze restoration by us, sign-up for our training course, coming in 2019
The Antique Bronze team recently undertook monument restoration work on The Aldersgate Flame. This is a special bronze located outside the entrance to the Museum of London. It is reputed to be the approximate location of John Wesley’s evangelical conversion in 1738. The English cleric and theologian went on to be one of the founding fathers of Methodism. He inspired its followers to right wrongs of the day, particularly with regard to social issues, such as prison reform and the abolition of slavery.
The mighty sculptural scroll features text from Wesley’s journal describing his conversion experience. Over time, the environment had done its worst and the monument’s surface had corroded quite comprehensively. Only small patches of patina were left intact.
In a situation like this monument restoration is the only way to proceed.
As the design of the sculpture centres around its text, visitors looked confused when guided there. They could no longer understand the statement that was intended to engage the public or appreciate its value because of the poor legibility and disfiguration of the surface. This is where champion of the monument, Alison Gowman, came to its rescue. She found funds to restore the monument.
Monument Restoration and Conservation Ethics
When a bronze surface is highly disfigured, a conservator has very few options open to them. Repatination involves the recolouring of a bronze’s surface by hand. The method employs almost identical methods to how a foundry would have finished the bronze when it was first made. This was a method that in previous eras was used so often that it was barely questioned. Today, we try to avoid treatments that do away with the passage of time in order to balance the original finish with acknowledgement of the object’s history.
Repatination, though, should make conservators pause. It goes against several principles that we try to uphold such as the desirability of techniques to be reversible and minimal intervention whenever possible.
Though technology has stormed ahead in the last decade, the repertoire of restoration technique suitable for large bronzes remains in the dark ages. Monuments which are hammered with rain, baked in the full sun and blown about by fierce urban winds often need repatination work in order to restore them to usefulness. So in this particular case, legibility trumps reversibility.
We were fortunate to have some segments of patina that were not ruined. This meant we were able to coax the new colour into existence and blend it with the segments that were already intact.
All Is Well Now
All is well now for The Aldersgate Flame and it is being enjoyed again by its visitors. Recently, Wesley Day was celebrated and the monument received a great deal of praise. Repatination should not necessarily be a technique conservators are fearful of using. Considered carefully and used sparingly, it continues to be a necessary technique in the preservation of outdoor sculpture.
Galvanic Corrosion is a type of corrosion that can happen to bronze sculptures that are electroplated. This was a method developed in the 19th century where a cheaper metal could be used to make up the form of a sculpture. A thin layer of brass or bronze would be added to give the aesthetic of a traditionally made item.
Galvanic corrosion occurs when the upper layer of the statue is nobler than the metal in the underlayer. If the upper layer comes under attack by something corrosive, or is porous, the less noble metal will begin to corrode preferentially.
In this situation, the bronze or brass provides a large cathodic area. Any small areas where the surface is compromised enables the anodic half-reaction to occur resulting in a large pit.
If the corrosion occurs beneath the bronze or brass surface, then the expansion of the corrosion products lifts the upper layer and detach it.
Recently we had a sculpture come in with just this issue. The underlying alloy was an iron-mixture plated with brass. When something corrosive splashed across it, the sculpture’s brass skin began to corrode in tiny areas. Once the upper layer was compromised, it began to rust below the surface. Soon the rust pushed through until there was a raised corrosion product in place. These small acne-like spots were spread all over the surface making the beautiful form of the sculpture highly disfigured.
If you’d like to learn more about corrosion and principles of bronze conservation, take a look at our online course, Bronze Behaving Badly.
Another good resource is Lyndsie Selwyn’s Book, Metals and Corrrosion