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Rust: Chemistry, Prevention, Removal, and Conversion

mhutchinson

Plastic
Joined
Jul 21, 2017
Good morning folks,
Long-time lurker here, finally ran out of old threads to sift through. Over the months I've spent reading about these things I consistently find good information on this particular forum, so here I am, a young, curious, and enthusiastic-but also inexperienced and probably naive-cowpoke walking through the double-doors of the saloon taking a seat next to the big boys! I'm also sarcastic and not entirely serious about half the time...

Anyway, I'm an amateur woodworker and I enjoy restoring antique tools. I worked in an auto body and mechanical shop throughout high school so I got a rough, general knowledge of some metalworking techniques but nothing substantial. I also took 4 semesters of chemistry in college recently so I understand the basics but, again, nothing substantial.

Over the years I've restored dozens of tools and spent a ridiculous amount of time sanding, grinding, polishing, sandblasting, etc. Part of my quest in tool restoration is to figure out the most effective techniques for various things. The current Holy Grail of endeavors is dealing with that timeless issue that's plagued industry since its birth: rust.

Over the years of exploring methods for rust removal I've tried a number of acids and chemicals, every type of mechanical removal techniques I could find, and a few experiments in converting red rust to the more stable iron oxide. Overall I feel fairly effective in my ability to simply remove rust.

But here's where things get complicated! A lot of old tools have a convenient (sarcasm) combination of rust and patina. The patina is desirable so removing the red rust without losing it is the goal. The old standby is steel wool or some other mild abrasive, and this works well enough with mild rust, but it is tedious and becomes ineffective pretty quickly when dealing with anything other than the mildest surface rust. My current thoughts on how to deal with this:
1) weaken the red rust-though not the patina-enough to make mechanical removal easier
2) convert the red rust (Fe[SUB]2[/SUB]O[SUB]3[/SUB]) to a more stable form like Fe[SUB]3[/SUB]O[SUB]4[/SUB].
3) there are some rust removing chemicals (namely Evaporust) that claim to use "chelating" agents


So far, idea #1 is not working. I've tried mild acids like oxalic and acetic acid-both in fairly dilute solutions-but these are still strong enough to damage the patina. Two variables to play with here:

A) strength of the chemical--perhaps there is something that is just strong enough to damage/weaken red rust but not quite strong enough to eat through patina

B) exposure time--I noticed when using vinegar to remove rust that there is varying results as an item is left in the solution for more or less time. If I timed the ordeal well I could often get rid of all the red rust without the vinegar eating into black rust very much but if I left an object in long enough the vinegar would begin to eat through the black rust that is often underneath the red rust, and I'd end up with a heavily-pitted piece of steel.


Idea #2 is not working yet but I haven't had enough time. My first thought was just to card off as much red rust as possible and then just apply oil over the rest, hoping that the blocking out of oxygen will eventually convert the red rust to black iron oxide. But this might take a while...the other method I've heard about but haven't tried yet is boiling. Still have to read more about that before I'd feel comfortable trying it.

So, that's where I am with my experiments. I'd love to hear suggestions or advice from others who have engaged in this tedious battle over the years. I'm also always looking for good, science-based sources of information on the chemistry beneath all these ideas because without science it's all just old wives' tales. For example, I'm assuming that patina is black iron oxide-Fe[SUB]3[/SUB]O[SUB]4[/SUB]-but I have no way to confirm that. Knowing exactly what it is and what's going on chemically would be helpful.

Any chemists in the house?

Thanks,
Matt
 

mhutchinson

Plastic
Joined
Jul 21, 2017
Ah, almost forgot: a resource and a more specific question:

I have read in a number of places that you can "force" a "patina" by soaking a steel object in vinegar (5% acetic acid). In my own experiments I definitely noticed a particular color to metal that was left in vinegar for a long time but I don't know that I would call it a patina. There is always some sort of black residue on the object after it's removed so perhaps that's what people are referring to as a patina. I never allowed this residue to dry on the metal because it wipes off without much trouble (usually ending up on every surface within a 5ft. radius of me) so I did not think it was a true patina. I also noticed that if I put an object that already had a patina into vinegar, the old patina would basically be dissolved.

However, here's an experiment done by a more legitimate scientific mind than myself:

http://corrosion-doctors.org/Experiments/iron-products.htm

So perhaps acetic acid can, in fact, create a true patina and I'm just not leaving the object in the vinegar long enough?
 

Reid Zeigler

Aluminum
Joined
Nov 5, 2005
Location
Pennsylvania
[QUOTE}

So, that's where I am with my experiments. I'd love to hear suggestions or advice from others who have engaged in this tedious battle over the years. I'm also always looking for good, science-based sources of information on the chemistry beneath all these ideas because without science it's all just old wives' tales. For example, I'm assuming that patina is black iron oxide-Fe[SUB]3[/SUB]O[SUB]4[/SUB]-but I have no way to confirm that. Knowing exactly what it is and what's going on chemically would be helpful.

Any chemists in the house?

Thanks,
Matt[/QUOTE]

Not a chemist, but worked in research my whole career, so I appreciate your scholarly approach, and share your frustration at the dearth of good information out there. I've had very good results with Evaporust, and you can see results on the antique equipment forum under Rambold lathe restoration. I showed an example of a 3-jaw scroll chuck that was very rusty and came out close to new looking. I've also had very good results with electrolysis and there's quite a bit out there on the chemistry. It's the best for total rust removal, but not always appropriate or practical. For metal that will be painted and that needs surface filling, I use a SEM product called Rust-Mort that's Phosphoric Acid, Chromic Acetate and Isopropanol. I've never had rust reappear and I can guess at the chemistry but would also like to see a diagram of the conversion process. -RZ
 
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Scottl

Diamond
Joined
Nov 3, 2013
Location
Eastern Massachusetts, USA
When firearms are browned or rust blued "carding" is part of the process. This removes the loose rust while leaving the patina, which is the desired goal. All a carding wheel amounts to is a fine gauge wire wheel that is not too aggressive if used with light pressure. I keep something along those lines mounted on a bench grinder and most of my "previously owned" tool acquisitions get to face the wheel along with a good oiling afterward. Some I brush more aggressively and then cold blue while others still have a brown patina that just gets oiled.

Small stuff can be gently brushed by hand using a suitably gentle wire brush.
 
Joined
Feb 4, 2004
Location
Metuchen, NJ, USA
Welcome aboard, Matt!

First of all, don't sell yourself short: four semesters of college chemistry is substantial in the sense that it gives you a solid background to understand the problem.

Second, you are seeking a scientifically-sound understanding of the available processes, which is laudable.

I'm going to throw out some material for additional research:

1) The OLDTOOLS archive. Search for old postings by Dr. George Langford regarding the "bucket-brigade" rust reaction caused by Chloride ions in the steel.

2) Dr. Langford has also posted in this forum. He is a retired metallurgist whose practice included university teaching and forensic metallurgy, among many other topics. www.georgesbasement.com

3) Collectors / Restorers of antique firearms face nearly identical challenges to restorers of antique tools. Hence, they are a prolific source of methods and information. (That's a big-bucks field; the top prices of old firearms are much higher than the top prices of old tools!)

My own humble observation is that removal of the surface rust often reveals hidden "pits." There is most often a Chloride ion at the bottom of each pit, merrily participating in a bucket-brigade reaction when conditions are right. The Cl ions came from human perspiration. The ONLY way to actually remove these ions, short of major abrasion, is electrolysis.

This is the same unstoppable "road salt" reaction that corrodes your automobiles! Once the road salt rusting starts, sanding to bright metal and repainting does not stop it. One must aggressively cut or grind away the steel with the embedded Cl ions <on edit> or use electrolysis.. <end edit>

If the item is pitted, then patina isn't your primary concern - it's STOPPING the rusting reaction that is going on at the bottom of the pits.

Electrolysis is particularly good at finding rust under japanning. Items which I though still had 80% japanning came out of the bath with maybe 25%! But, no foul because it really didn't have 80% to begin with!

Rust Prevention on bare steel: I just started using Fluid Film coating about 6 months ago. So far, I've been very pleased with it.

John Ruth
Who hopes this thread has a long and useful life!
 
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JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
It seems that "patina" and "flake rust" are chemically similar enough that they are attacked simultaneously. Chemical removal of rust also removes "patina".

Some methods result in a hard shell of black oxide.

Unfortunately, Fe2O3 is probably the MOST stable form.... at least under atmospheric conditions. Buried, other forms may be more stable. "Black oxide" finish will "rust" and turn to red rust, unless protected with wax or oil. Red rust seems to be the "end point".
 

Franz©

Aluminum
Joined
Feb 19, 2009
Location
South Ontario former USA
There's an encyclopedia to be written on rust removal and conversion, and there already exists two full volumes of disinformation on the process mislabeled "Electrolysis".
"Electrolysis" is really electroplating, and the only electrolytic action in the tank is ofr minimal water as occurs in any plating tank. We'll need at east a book on the difference between salt water caused rust and nonsalt containing rust.
Going to need a chapter on accumulating electrodes too, and minimally a chapter from guys who are sure carbon (Graphite) electrodes offer no advantage because they read on some site someplace where a guy hooked an elevator contact to his welder at 200 amps and it didn't derust the 4x8 sheet of steel any faster than the lawnmower blade he used in the B tank. Better add a chapter for the guys who insist on using Sodium Hydroxide and another for the high current group too. Most of the high voltage advocates died off forgetting to disconnect the tank before they reached in, so a page will cover them.

All I know is I can run my tank 24/7 at 24 volts 10 amps with graphite electrodes and filtration maintaining a clean clear electrolyte, and watch the rust walk off the object I'm cleaning.
It's a good method as long as the person doing it makes good connections and keeps grease & dirt out of the tank. It's a 2 step process in the case of salt water rust, possibly 3 to remove the salt first to prevent electrolyte contamination.
It will not maintain patina though, although that can be restored by allowing flash rust and polishing.
The process will work down to 31°f, and can be helped to heat itself by increasing current.

Chelation- is another whole volume unto itself. I do NOT encourage the use of overpriced miracle slop in a bucket sold at Horrible Freight or other vendors.
The process is well known and understood, and has probably been around for 100 years. Go to the nearby feed store, buy yourself a bag of cow molasses, and mix it up in a plastic bucket you can and should set outside away from your living area. The bucket will stink, it will grow mold, and it will attract flys and other creatures. The process is slow, and stops working below about 50°f. It is a very forgiving process unless you forget what you left in the tank for a month.
Molasses doesn't care if the rust is salt containing.
Months of scientific screwing around have demonstrated no gain by adding DC current to this process.

Vinegar & Muriatic acids will eat rust. They will also eat iron.
Neither belongs in any derusting process unless it is a high speed industrial process under constant monitoring.

If you have something you really want to screw up, use vinegar. What you pull out might look clean, but most iron that was there is gone and you have a hunk of carbon.

Phosphoric acid is both a remover and a converter, depending on the acid concentration. 4 - 8% by volume will convert rust to either a black or white phosphate coating depending on steel composition. Add some Magnesium to the solution and you get a slightly different coating simulating Parkerizing.
The nice thing about Phosphoric is it does NOT attack good steel. The second nice thing is the Iron Phosphate layer is bonded to the steel, and provides an excellent layer for paint & coating adhesion, eliminating the need to prime.
You can even tent and vaporize Phosphoric to treat oddly shaped objects.
The key to success with Phosphoric acid is complete wetting. That generally requires time with rust contacting acid.
There is a product line called POR based on marine phosphoric polymeric coatings that has developed a following. It is only a TEMPORARY coating, as is specified in the literature for use in marine environments. POR spends a lot on advertising, and people spend too much on POR products.

Oxcalic Acid works too, slow soak tank, and not really damaging to good steel. Just remember to rinse well.

Tannic acid is a converter, not as good as Phosphoric, but if you have tea sitting around, with lemon, NOT milk, why not try it.

Media blasting including water, will remove some of the rust you can see. It will also peen shut little rust gardens waiting for water and oxygen to grow and spall coatings off.

Soda blasting is not a process for removing rust. Soda is for removing "soft" deposits like tar and grease.

If money is no object in your consideration, red laser at high power will blow rust off surfaces.
 

Joe in NH

Diamond
Joined
Jul 28, 2007
Location
Stratham, Cow Hampshire
Very nice write-up. I think it was Vince Falter at Model 'A' Ford Garage ~ Model 'B' Ford Garage who awakened me to value of carbon electrodes Model A Ford Garage ~ Carbon Anode Electrolytic Rust Removal Method - but so far I have pretty much stuck with "disposable" iron - I have a surplus of 4" schedule 10 iron pipe in 4' lengths that were used as the center axle of utility cable spools - and these I don't mind losing.

I have been pretty successful with my steel pipe, a 12 amp battery charger, and sodium hydroxide (Robic drain cleaner) solution as the electrolyte. This does the conversion nicely but leaves the part "black" as in conversion to ferrous oxide - which is the black oxide which can be removed somewhat and will hold paint. To be REALLY sure before painting I do the Phosphate wash trick which leaves the surface "grey" but is perhaps even more resistant to reversion to red rust.

For parts I intend to remain "bright" I confess the fine wire wire wheel mentioned above is the option du jour for me. Still, the parts tend to black hue which I consider only a minor downside. If oiled regularly they are certainly slower to redden.

I think it was a southern museum which has outfitted an entire 19th century machine shop in 19th century tools and which they have done a MARVELOUS job at restoration. I commented here "How do they keep their bright-work so bright in that humid climate?" The answer I got here was "air conditioning."

Still, the question remains in my mind as HOW exactly did they get those machines to that condition in the first place? All I can think is when I made a surprise visit to Ed Battison at his house in Windsor, VT and he showed me his "back room machine shop." Which was a very typical shop to include a (probably) Atlas type shaper and a South Bend 10. I noted that chucked in the lathe was a very ornate ball-crank handle suitable for a Putnam planer - one which Ed owned and he apparently "improving the privilege" by taking skim cuts on that cast iron ball crank.

Given Ed's Smithsonian background I would not have thought Ed would so "modify" an existing handle - after all, its unrestored form showed the wear and tear of 130 years of use? Which is a kind of history all in itself?

Joe in NH
 

tdmidget

Diamond
Joined
Aug 13, 2005
Location
Tucson AZ
There's an encyclopedia to be written on rust removal and conversion, and there already exists two full volumes of disinformation on the process mislabeled "Electrolysis".
"Electrolysis" is really electroplating, and the only electrolytic action in the tank is ofr minimal water as occurs in any plating tank. We'll need at east a book on the difference between salt water caused rust and nonsalt containing rust.
Going to need a chapter on accumulating electrodes too, and minimally a chapter from guys who are sure carbon (Graphite) electrodes offer no advantage because they read on some site someplace where a guy hooked an elevator contact to his welder at 200 amps and it didn't derust the 4x8 sheet of steel any faster than the lawnmower blade he used in the B tank. Better add a chapter for the guys who insist on using Sodium Hydroxide and another for the high current group too. Most of the high voltage advocates died off forgetting to disconnect the tank before they reached in, so a page will cover them.

All I know is I can run my tank 24/7 at 24 volts 10 amps with graphite electrodes and filtration maintaining a clean clear electrolyte, and watch the rust walk off the object I'm cleaning.
It's a good method as long as the person doing it makes good connections and keeps grease & dirt out of the tank. It's a 2 step process in the case of salt water rust, possibly 3 to remove the salt first to prevent electrolyte contamination.
It will not maintain patina though, although that can be restored by allowing flash rust and polishing.
The process will work down to 31°f, and can be helped to heat itself by increasing current.

Chelation- is another whole volume unto itself. I do NOT encourage the use of overpriced miracle slop in a bucket sold at Horrible Freight or other vendors.
The process is well known and understood, and has probably been around for 100 years. Go to the nearby feed store, buy yourself a bag of cow molasses, and mix it up in a plastic bucket you can and should set outside away from your living area. The bucket will stink, it will grow mold, and it will attract flys and other creatures. The process is slow, and stops working below about 50°f. It is a very forgiving process unless you forget what you left in the tank for a month.
Molasses doesn't care if the rust is salt containing.
Months of scientific screwing around have demonstrated no gain by adding DC current to this process.

Vinegar & Muriatic acids will eat rust. They will also eat iron.
Neither belongs in any derusting process unless it is a high speed industrial process under constant monitoring.

If you have something you really want to screw up, use vinegar. What you pull out might look clean, but most iron that was there is gone and you have a hunk of carbon.

Phosphoric acid is both a remover and a converter, depending on the acid concentration. 4 - 8% by volume will convert rust to either a black or white phosphate coating depending on steel composition. Add some Magnesium to the solution and you get a slightly different coating simulating Parkerizing.
The nice thing about Phosphoric is it does NOT attack good steel. The second nice thing is the Iron Phosphate layer is bonded to the steel, and provides an excellent layer for paint & coating adhesion, eliminating the need to prime.
You can even tent and vaporize Phosphoric to treat oddly shaped objects.
The key to success with Phosphoric acid is complete wetting. That generally requires time with rust contacting acid.
There is a product line called POR based on marine phosphoric polymeric coatings that has developed a following. It is only a TEMPORARY coating, as is specified in the literature for use in marine environments. POR spends a lot on advertising, and people spend too much on POR products.

Oxcalic Acid works too, slow soak tank, and not really damaging to good steel. Just remember to rinse well.

Tannic acid is a converter, not as good as Phosphoric, but if you have tea sitting around, with lemon, NOT milk, why not try it.

Media blasting including water, will remove some of the rust you can see. It will also peen shut little rust gardens waiting for water and oxygen to grow and spall coatings off.

Soda blasting is not a process for removing rust. Soda is for removing "soft" deposits like tar and grease.

If money is no object in your consideration, red laser at high power will blow rust off surfaces.


:icon_bs:"Phosphoric acid is both a remover and a converter, depending on the acid concentration. 4 - 8% by volume will convert rust to either a black or white phosphate coating depending on steel composition. Add some Magnesium to the solution and you get a slightly different coating simulating Parkerizing."
It's a long way from magnesium to Manganese. Parkerizing is forming a coating of Manganese Phosphate on the steel. No magnesium involved.

RE: sodium hydroxide as an electrolyte: There is NO advantage. The electrolyte provides a means for electrons to travel from one electrode to the other. That is all. IF the item was to be left in a solution without current for an extended period of time the sodium hydroxide would be better at preventing rust. It is used as a feed water additive because rust will not occur at a ph above 9-10.
 

Franz©

Aluminum
Joined
Feb 19, 2009
Location
South Ontario former USA
:icon_bs:"Phosphoric acid is both a remover and a converter, depending on the acid concentration. 4 - 8% by volume will convert rust to either a black or white phosphate coating depending on steel composition. Add some Magnesium to the solution and you get a slightly different coating simulating Parkerizing."
It's a long way from magnesium to Manganese. Parkerizing is forming a coating of Manganese Phosphate on the steel. No magnesium involved.

There is a reason I rarely involve myself in rust removal and conversion threads.
I am now FINISHED with this one!
 

Joe in NH

Diamond
Joined
Jul 28, 2007
Location
Stratham, Cow Hampshire
RE: sodium hydroxide as an electrolyte: There is NO advantage. The electrolyte provides a means for electrons to travel from one electrode to the other. That is all. IF the item was to be left in a solution without current for an extended period of time the sodium hydroxide would be better at preventing rust. It is used as a feed water additive because rust will not occur at a ph above 9-10.

This was my take on the normally strong lye for use in a bath. All you're providing is ions for ionic transfer.

In the concentration necessary to support electrolysis, lye is pretty benign stuff. Think on the order of vinegar in the other direction electrochemically. With the current off (a prerequisite against heart failure) I have no problem immersing my hand in the solution to check/confirm distance between electrode and the part. The only side effect I notice is my hands come out "greasy" (basic solution remember) and the bath removes all the natural oils out of my skin leaving the hands dry and easily cracked in winter. Summer seems less of a problem.

Lye USED to be available at most hardware/homewares type store. Now with sodium hydroxide seemingly in demand by the Walter Whites of the world, its availability is much less. Hence the Roebic "Crystal Drain Opener" which is 99.8 percent sodium hydroxide. Draino:tm: contains aluminum to further the heating of the reaction and while it contains 80 percent plus sodium hydroxide, its use for electrolysis is to be discouraged.

Small tid-bits you pick up.

The Phosphoric Acid wash I use is "KleanStrip" Prep&Etch. About $15 a gallon at the big box stores. I have a spray bottle which I spray the newly electrolyzed part (or the cabinet blasted part) and this addresses any flash rusting which might occur. Careful not to inhale the mist. It will give anything it touches that "grey" cast. I have a steam pump waiting for paint now over a year on which I did the Prep&Etch. No sign yet of red on it.

Joe in NH
 

crrmeyer

Stainless
Joined
Nov 10, 2006
Location
Southern California
Chelation- is another whole volume unto itself. I do NOT encourage the use of overpriced miracle slop in a bucket sold at Horrible Freight or other vendors.
The process is well known and understood, and has probably been around for 100 years. Go to the nearby feed store, buy yourself a bag of cow molasses, and mix it up in a plastic bucket you can and should set outside away from your living area. The bucket will stink, it will grow mold, and it will attract flys and other creatures. The process is slow, and stops working below about 50°f. It is a very forgiving process unless you forget what you left in the tank for a month.
Molasses doesn't care if the rust is salt containing.
Months of scientific screwing around have demonstrated no gain by adding DC current to this process.

I use a lot of molasses. At $20 for 5 gal and diluted 8:1 with water, it goes a long way.

Observations:
1) De-grease metal with break cleaner
2) In general it does not remove paint (which usually I find is a good thing)
3) The bugs must be different in California - the ants and flys here hate the smell of molasses. But if you leave it long enough it will get gunk (mold?) on the top layer. Its cheap so dump it after each use. I usually put a loose fitting plastic bag or lid on the container
4) I find it works best fresh. The older it gets, the longer it takes.
5) It also can leave odd black stains on hardened vise jaws - more prevalent if you leave it in the bath too long or too old of a bath. Had to surface grind them off. Best to pull out hardened jaws too soon vs. too late.
6) I have seen two cases of hardened leaf type springs immediately failing after treatment. Hydrogen embridlement? Not sure but it was observed. So I do not use this method on springs.
7) I usually take a look at it daily. Stir it up daily too. Wash off with water when done, then dry and apply WD40.
8) Leaves a black oxide layer which can be scrubbed off with ScotchBrite and WD40. They apply preservative to prevent rust.
 

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
Most of what Franz wrote is good.

One thing should be mentioned, and that is the idea that phosphoric will not attack steel.

YES it is MOSTLY true. The exception is springs, some hardened steel, etc. ALL the processes have trouble with those.

The issue is "stress corrosion cracking". Where there is stressed material, the normally non harmful phosphoric (or other derusting material) can attack the steel at the point of maximum stress. So can electrolytic process, and most of the other derusting products also, potentially even the "chelating" products.

Springs can get cracked right across, and a pattern that looks like the pattern of color case hardening may be etched in hardened steel.

Just do not put springs in, especially not if they are compressed or stretched. And don't forget and leave hardened steel in for too long. The etching takes much longer than de-rusting. Phosphoric usually is finished de-rusting in 30 to 45 minutes, the etching takes several hours.
 

mhutchinson

Plastic
Joined
Jul 21, 2017
Not a chemist, but worked in research my whole career, so I appreciate your scholarly approach, and share your frustration at the dearth of good information out there. I've had very good results with Evaporust, and you can see results on the antique equipment forum under Rambold lathe restoration. I showed an example of a 3-jaw scroll chuck that was very rusty and came out close to new looking. I've also had very good results with electrolysis and there's quite a bit out there on the chemistry. It's the best for total rust removal, but not always appropriate or practical. For metal that will be painted and that needs surface filling, I use a SEM product called Rust-Mort that's Phosphoric Acid, Chromic Acetate and Isopropanol. I've never had rust reappear and I can guess at the chemistry but would also like to see a diagram of the conversion process. -RZ

Thus far I've come to the same conclusion--Evaporust is by far the best product I've found but electrolysis is just as effective. While the latter does require initial investment for a good setup, it's cheaper in the long run.
 

mhutchinson

Plastic
Joined
Jul 21, 2017
When firearms are browned or rust blued "carding" is part of the process. This removes the loose rust while leaving the patina, which is the desired goal. All a carding wheel amounts to is a fine gauge wire wheel that is not too aggressive if used with light pressure. I keep something along those lines mounted on a bench grinder and most of my "previously owned" tool acquisitions get to face the wheel along with a good oiling afterward. Some I brush more aggressively and then cold blue while others still have a brown patina that just gets oiled.

Small stuff can be gently brushed by hand using a suitably gentle wire brush.

My method so far-if I'm trying to save the patina-is the human-powered, elbow-greased version of that. Steel wool and fine wire brushes basically. So far that is the best method I've found.
 

mhutchinson

Plastic
Joined
Jul 21, 2017
Welcome aboard, Matt!

First of all, don't sell yourself short: four semesters of college chemistry is substantial in the sense that it gives you a solid background to understand the problem.

Second, you are seeking a scientifically-sound understanding of the available processes, which is laudable.

I'm going to throw out some material for additional research:

1) The OLDTOOLS archive. Search for old postings by Dr. George Langford regarding the "bucket-brigade" rust reaction caused by Chloride ions in the steel.

2) Dr. Langford has also posted in this forum. He is a retired metallurgist whose practice included university teaching and forensic metallurgy, among many other topics. www.georgesbasement.com

3) Collectors / Restorers of antique firearms face nearly identical challenges to restorers of antique tools. Hence, they are a prolific source of methods and information. (That's a big-bucks field; the top prices of old firearms are much higher than the top prices of old tools!)

My own humble observation is that removal of the surface rust often reveals hidden "pits." There is most often a Chloride ion at the bottom of each pit, merrily participating in a bucket-brigade reaction when conditions are right. The Cl ions came from human perspiration. The ONLY way to actually remove these ions, short of major abrasion, is electrolysis.

This is the same unstoppable "road salt" reaction that corrodes your automobiles! Once the road salt rusting starts, sanding to bright metal and repainting does not stop it. One must aggressively cut or grind away the steel with the embedded Cl ions <on edit> or use electrolysis.. <end edit>

If the item is pitted, then patina isn't your primary concern - it's STOPPING the rusting reaction that is going on at the bottom of the pits.

Electrolysis is particularly good at finding rust under japanning. Items which I though still had 80% japanning came out of the bath with maybe 25%! But, no foul because it really didn't have 80% to begin with!

Rust Prevention on bare steel: I just started using Fluid Film coating about 6 months ago. So far, I've been very pleased with it.

John Ruth
Who hopes this thread has a long and useful life!

Thanks for the input, John! Dr. Langford's website looks like it will be a valuable resource.

And on the note of chloride ions--I didn't realize this actually but given the road salt example, it makes sense. And if it is the case with a lot of the old tools I am working with, then gentle abrasion of surface rust followed by oiling sounds like it may not be sufficient in the long term. Looks like I've got more reading to do.
 

Reid Zeigler

Aluminum
Joined
Nov 5, 2005
Location
Pennsylvania
Thus far I've come to the same conclusion--Evaporust is by far the best product I've found but electrolysis is just as effective. While the latter does require initial investment for a good setup, it's cheaper in the long run.

I haven't tried molasses but here's my results from a couple of weeks ago with Evaporust. Full disclosure - After 24 hours I disassembled the entire chuck, brushed with a brass brush on a Dremel type tool, polished with Simichrome, and sealed with museum wax, so I wouldn't call it just a dip and dry process. The parts came out dull gray and needed a little work.
165874015.jpg
 

mhutchinson

Plastic
Joined
Jul 21, 2017
It seems that "patina" and "flake rust" are chemically similar enough that they are attacked simultaneously. Chemical removal of rust also removes "patina".

Some methods result in a hard shell of black oxide.

Unfortunately, Fe2O3 is probably the MOST stable form.... at least under atmospheric conditions. Buried, other forms may be more stable. "Black oxide" finish will "rust" and turn to red rust, unless protected with wax or oil. Red rust seems to be the "end point".


Haha! Spoken like a true chemistry professor. I suppose red rust is, thermodynamically speaking, the most stable.
 

mhutchinson

Plastic
Joined
Jul 21, 2017
On the note of abrasives...it seems to me that, in situations where you want to retain the patina or bluing on a piece, the best solution is a very fine wire brush or wheel. The best I've seen are the ones used by gunsmiths for rust bluing such as this:

GROBET FILE CO. OF AMERICA INC .25" STAINLESS STEEL BRUSHING WHEELS | Brownells

Another option is the synthetic abrasives like the 3M radial bristle brushes:

http://www.3m.com/3M/en_US/company-...ial-Bristle-Brush?N=5002385+3293242167&rt=rud

I've used these for polishing before but never attempted rust removal with one. Anyone have any experience comparing the two? In my previous, simpleton thought process I figured the only variable with abrasives was coarseness-how big of a scratch it makes-but maybe it's more complicated than that...like everything else in the world...
 








 
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