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Post by ipostswords on May 11, 2023 14:51:03 GMT
I recently did a project conserving an antique Qajar era Iranian sabre. This sword had widespread and elaborate etched decorations but was plagued with rust of varying thicknesses and forms. I treated it with EDTA, a chelating agent, which very effectively removed most of the unstable corrosion products, while leaving some black, stable corrosion products intact. I detailed the entire process in a video, which I will link, as well as in some photos I will be attaching. Here is the condition as shipped from the auction (before oiling) As you can see, the hilt and area under the langets were heavily corroded. Once oiled, but before work commenced, it looked like this: The method I used relied on making an EDTA-Agar gel, which was painted onto the blade in sections. This is what it looks like freshly applied (after cleaning the blade with alcohol) Once the gel has had time to react, it takes on a yellow color and the edges turn red where oxygen is able to dissolve into the gel and react with the suspended chelated iron After removal, a substantial amount of the corrosion is removed. It took several applications per region of the blade to get the desired level of chelation. the hilt took upwards of 6 layers of gel, each acting for 1hr. After treatment, the etchings are well preserved. The brazed sheet steel hilt is free of much of the active corrosion, and the braze lines are visible again. Additionally, some faint lines can be seen converging on the langet on one side. The hilt took a lot longer to chelate, so 0.5% oxalic acid was added to the solution to aid in solubilizing the iron oxide as well as increase the affinity of the EDTA. This did change the texture of the gel, making it paste like. The hilt was cleaned with alcohol wipes and lightly buffed with paper towels to remove superficial corrosion that results from the chelation process before oiling. Overall, the method was extremely controlled. it allowed for precise placement of the gel, either painted on while liquid or applied in pre-cast sheets under the langets. There is no discernible loss of detail in the etching. The main issue with the workflow is how long it takes, this was a 4 day project. But I did not want to use any methods that risked the sword. This process is adapted from these papers. www.sciencedirect.com/science/article/pii/S1296207421001333www.mdpi.com/2310-2861/9/3/191Regarding "conservation" vs "restoration": This is a ferrous artefact. Conserving it means addressing the corrosion. Iron oxide doesn't form a sacrificial oxide layer like copper alloys - and therefore cannot be left untreated. Even with a protective layer like microcrystalline wax, corrosion slowly degrades iron objects. It is, therefore, indeed a form of conservation. If this was not done, the object would not be preserved for future generations. Video covering the whole process (1hr30m):
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Post by mrstabby on May 11, 2023 18:41:49 GMT
Why do you use oxalic acid specifically? I have used citric acid on rust, and the steel after looked very similar to the EDTA result, and it worked rather quickly, a few minutes, but it wasn't nearly as bad as yours. Acetic acid does not give as good a finish as citric acid in my experience. I have read that you could use a catalyst like sodium bicarbonate to speed up the reaction, did you use only EDTA or some catalyst as well?
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Post by ipostswords on May 12, 2023 3:50:01 GMT
Why do you use oxalic acid specifically? I have used citric acid on rust, and the steel after looked very similar to the EDTA result, and it worked rather quickly, a few minutes, but it wasn't nearly as bad as yours. Acetic acid does not give as good a finish as citric acid in my experience. I have read that you could use a catalyst like sodium bicarbonate to speed up the reaction, did you use only EDTA or some catalyst as well? I used oxalic acid for two main reasons. Firstly, it was one of the methods investigated in the papers and I didnt want to venture too far from them. Secondly, because I've used oxalic acid before and am thus familiar with its working time. I have used it on a pattern welded pala and a pattern welded yatagan as an etchant. I could have made this entire process a lot faster if I used higher concentrations or tried to catalyse the reaction, but I didnt particularly want to speed up the reaction too much the first time I was using the process, as I was concerned about the reaction going too far. In the future when using these gels, I will likely mess with concentrations and additive to optimise it. I have a Golia / heavily curved tulwar I need to work on, so when I do that I will probably do a series of spot tests with different gel chemistries.
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Post by mrstabby on May 12, 2023 7:51:20 GMT
There are also some shenanigans you could try with electrochemistry. I am not sure, how well this works, never tried it for rust, but you could reduce some rust back into its iron form, which would mean less pitting. I think the it might work well on very heavily damaged blades to rescue as much material as you can. I worked a bit with EDTA, but I have forgotten much. I can't really say, but I think chelation is't the part that removes the rust. EDTA is an acid itself, it would dissolve the rust, then capture the Fe ion. I don't think it will break the ion directly out of the rust. The rust removal will be faster if something removes the free Fe ions from the solution, but my guess is any other acid like oxalic, citric or tannic will give the same finish in the end. Don't add acid if you try the sodium bicarbonate catalyst, since bicarb makes the solition a bit more basic an thats the point, EDTA works better in basic environments.
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Post by ipostswords on May 12, 2023 7:57:54 GMT
There are also some shenanigans you could try with electrochemistry. I am not sure, how well this works, never tried it for rust, but you could reduce some rust back into its iron form, which would mean less pitting. I think the it might work well on very heavily damaged blades to rescue as much material as you can. I worked a bit with EDTA, but I have forgotten much. I can't really say, but I think chelation is't the part that removes the rust. EDTA is an acid itself, it would dissolve the rust, then capture the Fe ion. I don't think it will break the ion directly out of the rust. The rust removal will be faster if something removes the free Fe ions from the solution, but my guess is any other acid like oxalic, citric or tannic will give the same finish in the end. Don't add acid if you try the sodium bicarbonate catalyst, since bicarb makes the solition a bit more basic an thats the point, EDTA works better in basic environments. "Shenanigans with electrochemistry" is precisely one of the methods used in the original papers, they used potassium nitrate as a neutral electrolyte in a gel, and then performed electrolysis using the target object as the working electrode with a stainless steel counter electrode. Its something I will experiment with once I get some KNO3 in. Regarding how well the EDTA works at different pH levels, I can run some tests on this too. I have some scrap antique wrought iron I can forcefully corrode and run a full panel of tests.
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Post by mrstabby on May 12, 2023 9:16:42 GMT
Depending on your location KNO3 could be hard to procure. Be sure it won't get you on any lists before you buy some. Sodium bicarbonate should work as an electrolyte as well and won't get you into trouble.
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Post by ipostswords on May 12, 2023 13:04:53 GMT
Depending on your location KNO3 could be hard to procure. Be sure it won't get you on any lists before you buy some. Sodium bicarbonate should work as an electrolyte as well and won't get you into trouble. I don't want to be using a base as the electrolyte, the idea is it should be neutral.
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Post by ipostswords on May 12, 2023 13:16:42 GMT
I took a look at this guideline from the DOW chemical company, and the section on iron chelates notes that higher pH's (that is to say, basic conditions) favor hydrolysis of the iron and for iron, at least, it is stable at lower pH. www.dow.com/content/dam/dcc/documents/en-us/app-tech-guide/113/113-01388-01-chelation-chemistry-general-concepts-of-the-chemistry-of-chelation.pdfFrom my understanding of this, once the solution is sufficiently basic the EDTA can no longer even form is coordination bonds with the iron ions, because "As the pH of an aqueous solution of ferric EDTA is increased precipitation of ferric hydroxide begins to occur at a pH of 8.0 and the chelate is completely converted to free EDTA and ferric hydroxide by a pH of 12.0". That is to say, the EDTA is free. Honestly, most of the information on EDTA chelation of iron is in respect to things like titrations and iron in solution, so I am definitely going to need to do a series of tests to see the practical effects in the context of rusted steel objects.
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Post by mrstabby on May 12, 2023 13:46:17 GMT
For chelation to happen it the iron needs to be in solution first. So all of this won't be any help to you at all. It's more a guide on how to release the iron from the EDTA. As I said, I doubt the chelation effect is the primary reason EDTA can take away rust, its more likely the acidity of EDTA itself, but taking the Fe3+ ions out of solution (chelate them) wil make space for more iron to go into solution. But to get the Fe(III)O to release the Fe3+ you need an acid first. Fe(III)O + 2H+ --> Fe3+ + H2O The more Fe3+ is in solution, the slower the process goes. But if you steadily remove the Fe3+ by catching it with EDTA the process can go on for longer and you get off more rust. The basic catalyst makes the EDTA release the iron as FeOH and the EDTA is free to go catch another Fe3+. But the basic solution won't be able to dissolve the rust, I think the basic environment I had in my mind was meant to free the EDTA for later reuse in titration, not with rust itself. I bet EDTA + a bit of organic polyvalent acid (citric, oxalic, tannic etc) will produce the best outcomes with a single application. On the other hand multiple application and cleaning cycles with the acids alone will probably get the same result but cheaper. 100g EDTA cost as much as 2kg citric acid where I live.
BTW A solution of KNO3 will have a slight acidic pH, 6.2 at 10%. My guess is that nitrides are used since the other neutral-ish salts, chlorides and sulfates, could actually damage steel. PH of sodium bicarbonate would be around 8, but you could create a buffer solution thats exactly at pH7. Depending how serious you are abou the electrolyte being neutral. Buffer solutions make good electrolytes, but as I said, some salts could damage steel.
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Post by ipostswords on May 13, 2023 4:34:50 GMT
For chelation to happen it the iron needs to be in solution first. So all of this won't be any help to you at all. It's more a guide on how to release the iron from the EDTA. As I said, I doubt the chelation effect is the primary reason EDTA can take away rust, its more likely the acidity of EDTA itself, but taking the Fe3+ ions out of solution (chelate them) wil make space for more iron to go into solution. But to get the Fe(III)O to release the Fe3+ you need an acid first. Fe(III)O + 2H+ --> Fe3+ + H2O The more Fe3+ is in solution, the slower the process goes. But if you steadily remove the Fe3+ by catching it with EDTA the process can go on for longer and you get off more rust. The basic catalyst makes the EDTA release the iron as FeOH and the EDTA is free to go catch another Fe3+. But the basic solution won't be able to dissolve the rust, I think the basic environment I had in my mind was meant to free the EDTA for later reuse in titration, not with rust itself. I bet EDTA + a bit of organic polyvalent acid (citric, oxalic, tannic etc) will produce the best outcomes with a single application. On the other hand multiple application and cleaning cycles with the acids alone will probably get the same result but cheaper. 100g EDTA cost as much as 2kg citric acid where I live.
BTW A solution of KNO3 will have a slight acidic pH, 6.2 at 10%. My guess is that nitrides are used since the other neutral-ish salts, chlorides and sulfates, could actually damage steel. PH of sodium bicarbonate would be around 8, but you could create a buffer solution thats exactly at pH7. Depending how serious you are abou the electrolyte being neutral. Buffer solutions make good electrolytes, but as I said, some salts could damage steel.
Regarding your final point, the concentration used in the papers was 1%, which explains why it was closer to neutral there than in your10% example. Buffered solutions would probably be the way to go, just need to be mindful of what salts are being produced as a result of the buffer chemistry.
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Post by mrstabby on May 13, 2023 9:53:02 GMT
Ammonium acetate buffer solutions are available for pH7 and it should not be corrosive. Theoretically.... You would need to try it to be sure. The neutral pH alone does not mean it isn't corrosive.
There are other ways a solution can corrode metal, in the electrochemistry pH should not matter that much, since you force the reaction to go one way via electricity.
One thing when doing electrolytic reduction to keep in mind: The thing you try to derust can't have any othe metals on it or you risk bad side reactions.
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Post by blackprince on May 17, 2023 2:17:59 GMT
Depending on your location KNO3 could be hard to procure. Be sure it won't get you on any lists before you buy some. Sodium bicarbonate should work as an electrolyte as well and won't get you into trouble. Stump remover is readily available in my neighborhood. It’s mostly KNO3.
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Post by mrstabby on May 17, 2023 6:25:22 GMT
Depending on your location KNO3 could be hard to procure. Be sure it won't get you on any lists before you buy some. Sodium bicarbonate should work as an electrolyte as well and won't get you into trouble. Stump remover is readily available in my neighborhood. It’s mostly KNO3. They have other stuff added to them, so I would advise against it. Or at least test it on something expedable. If you are doing this electrochemically I would go for pure KNO3.
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Post by Sir Thorfinn on May 17, 2023 13:02:12 GMT
This is fascinating. Love it. What are your thoughts on things like Evaporust?
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Post by mrstabby on May 17, 2023 15:21:32 GMT
This is fascinating. Love it. What are your thoughts on things like Evaporust? Hard to say what exactly it does since no information on the ingredients is out there. The reusabiltiy is somewhat wierd to me. I have never used it to be honest. I like citric acid. Very cheap and effective. Since Evapo-Rust is almost neutral I can't really say how it works. Might be just the right chelator that can rip apart rust atoms without acidity but there would need to be something else, that releases the iron in some insoluable form from the complex, or it would't be able to be reused. The chelator would rip the iron off and keep it, like gollum did the ring, and then just be happy like this and wouldn't attempt to break off another atom from the rust.
The other possibility needs some background. If you put rust in water a tiny bit will always dissolve, until no more can be added, like sugar in water. If you remove the dissolved ions from the water, more can dissolve after. So a small bit of iron dissolves, the chelator catches it and this way takes it out of thesolution, so more iron can dissolve. This would be very slow, unless you boil the liquid or add something that can free up the iron quicker. Since EDTA is acidic, it can go both ways, depending on the acidity of the solution, thats what I got out of the texts I read. Seems EDTA in a basic environment and Thiourea Dioxide together would remove the most rust. The Thiourea seems to help dissolve rust, edta catches it and the basic environment releases the iron as FeOH, which is insoluable in water and falls out as white flakes. It has been used to combat corrosion in factories.
I have seen a few tests of Evapo-Rust and they don't seem to show a game changer. It is relatively slow and the end product doesn't look different than acid baths to me, the biggest positive is that it isn't acidic, so you don't have as much cleanup to do, and the datasheet says its not toxic too. I also don't derust big stuff, it might be worth it then because of its reusability.
I wonder how many times it can be reused.
I have to say one last thing though, vinegar does not work as well as citric, phosphoric or oxalic acid does, not by a long shot. It never worked well for me to remove rust, the finish just didn't look good, the citric acid did much better, and left bare metal.
EDIT: After looking up a few other videos on Evapo-Rust I am pretty sure it is not directly dissolving the rust, only helping to dissolve it by taking away the iron ions, thats why it's slow. It would probably be faster when heated. And somebody said 5l Evaporust can dissolve 3kg rust, so it might not even get regenerated, probably just a chelator that can take up iron, maybe even EDTA with an added buffer to stay neutral.
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Post by ipostswords on May 18, 2023 8:22:59 GMT
This is fascinating. Love it. What are your thoughts on things like Evaporust? Hard to say what exactly it does since no information on the ingredients is out there. The reusabiltiy is somewhat wierd to me. I have never used it to be honest. I like citric acid. Very cheap and effective. Since Evapo-Rust is almost neutral I can't really say how it works. Might be just the right chelator that can rip apart rust atoms without acidity but there would need to be something else, that releases the iron in some insoluable form from the complex, or it would't be able to be reused. The chelator would rip the iron off and keep it, like gollum did the ring, and then just be happy like this and wouldn't attempt to break off another atom from the rust.
The other possibility needs some background. If you put rust in water a tiny bit will always dissolve, until no more can be added, like sugar in water. If you remove the dissolved ions from the water, more can dissolve after. So a small bit of iron dissolves, the chelator catches it and this way takes it out of thesolution, so more iron can dissolve. This would be very slow, unless you boil the liquid or add something that can free up the iron quicker. Since EDTA is acidic, it can go both ways, depending on the acidity of the solution, thats what I got out of the texts I read. Seems EDTA in a basic environment and Thiourea Dioxide together would remove the most rust. The Thiourea seems to help dissolve rust, edta catches it and the basic environment releases the iron as FeOH, which is insoluable in water and falls out as white flakes. It has been used to combat corrosion in factories.
I have seen a few tests of Evapo-Rust and they don't seem to show a game changer. It is relatively slow and the end product doesn't look different than acid baths to me, the biggest positive is that it isn't acidic, so you don't have as much cleanup to do, and the datasheet says its not toxic too. I also don't derust big stuff, it might be worth it then because of its reusability.
I wonder how many times it can be reused.
I have to say one last thing though, vinegar does not work as well as citric, phosphoric or oxalic acid does, not by a long shot. It never worked well for me to remove rust, the finish just didn't look good, the citric acid did much better, and left bare metal.
EDIT: After looking up a few other videos on Evapo-Rust I am pretty sure it is not directly dissolving the rust, only helping to dissolve it by taking away the iron ions, thats why it's slow. It would probably be faster when heated. And somebody said 5l Evaporust can dissolve 3kg rust, so it might not even get regenerated, probably just a chelator that can take up iron, maybe even EDTA with an added buffer to stay neutral.
" maybe even EDTA with an added buffer to stay neutral." - from my understanding, this is exactly what evaporust is. crcindustries.com.au/products/ds/sds-EVR1.pdfIt is a chelator at 10-15%, with a surfactant. Hypothetically I could try to go to my old lab and ask them to run some on the mass spectrometer and make sure, but it's not worth it.
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Post by mrstabby on May 18, 2023 8:56:13 GMT
I wonder how the EDTA (or any other chelator) would act in the presence of other metals, like a silver inlay. I bet it would get damaged as well. It would surely eat away at anything containing copper. EDTA likes iron and copper better than silver, still I wonder if noble metals wouldn't get some pitting as well.
For time reduction, the EDTA should work much better when its warm, I think even at 50°C the reaction would speed up significantly (it depends on what temperature your test was done, but if it was done at 20-25°C I bet you could maybe even half the time by heating it to 50°C). But I don't know how warm the agar can get until it's not gel any longer. Something worth trying would be a different holding material, like a polymer instead of the agar, then you could heat it better. Some newer gels can be stable beyond 100°C.
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Post by larason2 on May 18, 2023 14:48:04 GMT
A note on EDTA, it's quite toxic if swallowed, so use gloves or wash your hands after using it. Its chemistry is quite complex. I used it when I worked in a lab to make solutions with precise calcium concentrations. It preferentially binds calcium when in the presence of other cations. These cations have more than one positive group in just the right configuration to form coordinating bonds on metal ions. The space between the groups determines which anions are more likely to bond. I suspect it's used here because it can bond iron, but its bonding strength and affinity isn't as strong as other compounds. So it removes the rust slower than other agents, which is desirable in conservation. I'm not sure I'm going to try this, because I feel its too toxic, but I'll keep it in mind in case I have a project in the future that would benefit from it!
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Post by ipostswords on May 18, 2023 14:51:19 GMT
I wonder how the EDTA (or any other chelator) would act in the presence of other metals, like a silver inlay. I bet it would get damaged as well. It would surely eat away at anything containing copper. EDTA likes iron and copper better than silver, still I wonder if noble metals wouldn't get some pitting as well. For time reduction, the EDTA should work much better when its warm, I think even at 50°C the reaction would speed up significantly (it depends on what temperature your test was done, but if it was done at 20-25°C I bet you could maybe even half the time by heating it to 50°C). But I don't know how warm the agar can get until it's not gel any longer. Something worth trying would be a different holding material, like a polymer instead of the agar, then you could heat it better. Some newer gels can be stable beyond 100°C. The gel process is applied hot, at the boiling point of the Agar gel
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Post by mrstabby on May 18, 2023 15:00:02 GMT
I have never heard that EDTA is toxic, the LD50 for rats is like 1g/kg. It can deprive the body of calcium, yes, but I wouldn't call it toxic. It is used in medicine to remove heavy metals from the digestive tract and blood, it likes the heavy metals better than calcium. As far as I know it likes lead the best, then iron, cobalt, copper... I don't remember the rest. I studied chemistry, have not done much with EDTA, more other complexes.
It can give you organ damage, but aspirin can do that too. Not that you should't be careful, but a drop will not kill you.
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