More metal bluing

[BobL]

About 3 years ago I set up a small metal bluing tank bluing and posted a few details a a couple of photos in this post.
http://www.woodworkforums.com/showthread.php?t=155843&highlight=metal+bluing

Since then I have blued some small pieces, and have also have received a few PMs about what I do.
What I have been meaning to do for a while is post a few more details of the process and include some more pics.

The pieces I am bluing are the bearing housing, wheel collar/flange and table hold down screw for the thin kerf cut off saw I made a couple of weeks back.

This is the bearing housing - not the best bit of machining but it works and it's done now and that's what I have to work with.
http://www.woodworkforums.com/attachment.php?attachmentid=354156&stc=1

The recipe I used was almost identical to what I have posted before but here it is again but this time with pictuires.

1) Polish the metal to as high a shine as you desire for the final finish.
The smoother the finish the more reflective and protective the coating will be.
Mine have only been polished using a scotchbrite wheel so it was more of a matt polish.
Sorry no pics of this stage

2) Wash the oil and gunk from the metal parts by boiling is a weak (5%) solution of sodium carbonate [(Foot spa salts) a 500g bag costs about $5 a bag at coles] for an hour

3) From this point onwards handle the parts with rubber gloves. I use those disposable latex type.
Rinse the parts with distilled water and suspend pieces in the bluing chamber from pieces of wire.
Make sure the chamber is sealed to keep in the fumes or they will corrode all ferrous stuff they come into contact with.
The bluing chamber contains two open containers one with concentrated HCl and the other with concentrated HNO3.
http://www.woodworkforums.com/attachment.php?attachmentid=354157&stc=1

4) After the parts have formed a coating of rust [this can take anywhere from a couple to 12 hours] remove from chamber
This is they look like after the 4th pass, after the first pass they come a much brighter orange (i.e. rust)
http://www.woodworkforums.com/attachment.php?attachmentid=354158&stc=1

5) Place the rusty looking pieces into a clean container of fresh, boiling distilled water.
I use a large clean stainless steel saucepan on an old electric frying pan and hook the pieces onto the side of the saucepan.
Boil for ~one hour, rust colour should go black.
http://www.woodworkforums.com/attachment.php?attachmentid=354162&stc=1

6) Remove and allow parts to dry.
This is typically how they look after boiling
It doesn't matter if they are patchy, underneath that grey colour on the large middle piece will be a black sooty layer of black oxide.
http://www.woodworkforums.com/attachment.php?attachmentid=354160&stc=1

7) Then remove the loose "soot", which is black iron oxide,from all surfaces using a fine stainless wire brush and/or fine steel wool.
Fine steel wool works well on flat surfaces but brushes will work better on threads and into nooks and crannies.
The amount of soot that comes off looks like you are taking it all off but that is normal.
Rub hard enough to achieve a smooth surface but not so hard as to get it back to bare metal
This shows the amount that comes off 0 quite a bit and make a mess hence the need for gloves.
http://www.woodworkforums.com/attachment.php?attachmentid=354161&stc=1

After the first pass through the bluing tank the steel might only have changed to a medium grey like this but this is entirely normal .
http://www.woodworkforums.com/attachment.php?attachmentid=354163&stc=1


8) Repeat steps 3 - 7 until the desired depth of colour and protection is obtained.
This means somewhere around 10 passes.

Here's what they are looking like after 5 passes (NB the soot has been removed before the photo was taken)
http://www.woodworkforums.com/attachment.php?attachmentid=354159&stc=1
They look nice and black in the photo but more cycles will make a more lustrous bluer hued colour that is more protective. This batch is going dark a lot quicker than usual - i think it may be because I have been a lot more careful about keeping things clean, i.e. double rinsing the saucepan after every pass etc.

It is interesting to see the pieces slightly change colour hue after every few cycles. first they are grey, then dark brownish and then faintly blue and then full on black.
After 5 cycles I now switch to superfine steel wool

9) finally Heat the parts in hot oil (I use new engine oil in another stainless steel saucepan on the electric frypan) for a couple for hours. Remove parts from oil, let cool and wipe off excess oil. For maximum protection the parts should be kept lightly oiled. If they develop surface rust they can be re-blued as per new pieces.

Thats it.
It's a very slow process but the finish is supposed to be one of the more robust of the bluing methods. It's not used much because it is so slow.

[Stustoys]

Hi Bob,
Thanks for the write up.


The bluing chamber contains two open containers one with concentrated HCl and the other with concentrated HNO3.
Is this the sort of thing one can get hold of without to much trouble?

Stuart

[WoodBee2]

Hi Bob,
Thanks for the explanation. Sounds like something I will try in the future. I have a couple of questions if you don't mind:
Why heating in oil for so long? Isn't it enough if the formed layer is saturated with oil (and the heating to make it more "liquid" and "wet" better?)
I use the water that accumulates in the dryer when we dry our clothes as distilled water. Would that be good enough for this application? (might contain a little pocket fluff ;-) )
In your previous post you also mentioned another acid that could be used. Is there any difference in application or result?

Thanks
Peter.

[BobL]

Hi Bob,
Thanks for the write up.

Is this the sort of thing one can get hold of without to much trouble?

Stuart

For Concentrated HCl I used Diggers Spiirts of Salts from Bunnings.
Nitric acid is not so easy to get but Sulphuric acid can be substituted for nitric..

Diluter forms will also work but take longer although some reduction in time can be achieved by then using a smaller chamber/

[BobL]

Hi Bob,
Thanks for the explanation. Sounds like something I will try in the future. I have a couple of questions if you don't mind:
Why heating in oil for so long? Isn't it enough if the formed layer is saturated with oil (and the heating to make it more "liquid" and "wet" better?)

I would not be heating the coated object with something like a flame and then dunking it it oil as that may form a coating of scale and polymerised oil which ruins the finish and will interfere with any fine fitting required. The major benefit of this type of finish is that it is very thin which means machined parts will easily go back together again.
If I don't need the fine fit or finish and just want rust protection then because it takes so long I wouldn't bother to blue the metal and heating and dunk in oil .

The length of time in the hot oil was in the recipe I got from Guy Leotards book.
I reckon one could get away with a shorter time than an hour but as far as I can I have stuck to his recipe.


I use the water that accumulates in the dryer when we dry our clothes as distilled water. Would that be good enough for this application? (might contain a little pocket fluff ;-)
As long as the water accumulator container is clean, no bugs or moulds etc. While the fluff will contain some impurities this water should be better than any tap water and should work OK.
The cleaner and purer everything is the stronger the coating.
Because of the cleaning requirements and the number of passes needed to get a good coating the amount of distilled water needed is quite high (I go though about 40L to do a batch) and this can be expensive if you need to buy it. The volume of water could be scaled back considerably by using a smaller saucepan


In your previous post you also mentioned another acid that could be used. Is there any difference in application or result?
Yes sulphuric acid - sometimes found in brick cleaners - can be used. There is no difference in the way it is done or the end result except that concentrated Sulphuric acid probably smells worse than the other

[Hornetb]

This technique is called rust bluing and has been used on firearms for 100+years. Pretty easy to do as you say, just labour intensive.

I use a wipe on solution of a mix of hydrochloric acid (battery acid), nitric acid and iron filing and distilled water. The technique you use is called fuming.

The mix I use is 20ml Nitric Acid (I think its about 68% conc), 13ml hydrochloric acid (30% conc) and then keep adding iron filing until the solution stops reacting then add the ACID TO THE WATER (160mls of water). Makes about 200mls, store it and protect from light. Hazardous note: Adding the iron to the acid produces a bubbling reaction, heat, and puts off brown nitrogen dioxide gas which is not good for you. Best done in a fume hood, but I guess you could just try running away.

Polish your parts (no need to go above 320grit really). Then degrease well, and from this point on handle only with gloves:
http://i65.photobucket.com/albums/h215/HornetB/Rust%20bluing%20Weatherby/20150608_202208_zpsq2hfm62x.jpg (http://s65.photobucket.com/user/HornetB/media/Rust%20bluing%20Weatherby/20150608_202208_zpsq2hfm62x.jpg.html)

Wipe on a very thin layer of the acid mix, just enough to wet the part. Put them in a humid environment and let them rust (usually overnight):
http://i65.photobucket.com/albums/h215/HornetB/Rust%20bluing%20Weatherby/20150609_184801_zpsiad3wbkl.jpg (http://s65.photobucket.com/user/HornetB/media/Rust%20bluing%20Weatherby/20150609_184801_zpsiad3wbkl.jpg.html)

http://i65.photobucket.com/albums/h215/HornetB/Rust%20bluing%20Weatherby/20150609_184711_zpstpqhi8ie.jpg (http://s65.photobucket.com/user/HornetB/media/Rust%20bluing%20Weatherby/20150609_184711_zpstpqhi8ie.jpg.html)

Dont let them rust too long or the parts will pit. Just enough to get a brown dust on them. The above pics are probably a bit too far, but I repolished and started again on one of them. The other part was saved. Boil in distilled or deionised water (can get 2 litres from the supermarket in the ironing section for about a $1.50) until the part turns black. I reuse the water a few times, so for small parts I only need maybe 4L total for the whole job. You just need enough to cover the parts while boiling.

Pull them out and blow the water off with the air compressor to stop more flash rusting. The rub down with a fine carding wheel (from Brownells) or DEGREASED 0000 steel wool.

Repeat.

Produces a pretty nice and durable finish if you ask me :2tsup:
http://i65.photobucket.com/albums/h215/HornetB/Rust%20bluing%20Weatherby/20150613_135649_zpst0nh5o2o.jpg (http://s65.photobucket.com/user/HornetB/media/Rust%20bluing%20Weatherby/20150613_135649_zpst0nh5o2o.jpg.html)

http://i65.photobucket.com/albums/h215/HornetB/Rust%20bluing%20Weatherby/20150613_135659_zpskcecszgy.jpg (http://s65.photobucket.com/user/HornetB/media/Rust%20bluing%20Weatherby/20150613_135659_zpskcecszgy.jpg.html)

http://i65.photobucket.com/albums/h215/HornetB/Rust%20bluing%20Weatherby/20150613_135715_zpsvb11ubhs.jpg (http://s65.photobucket.com/user/HornetB/media/Rust%20bluing%20Weatherby/20150613_135715_zpsvb11ubhs.jpg.html)

http://i65.photobucket.com/albums/h215/HornetB/Rust%20bluing%20Weatherby/20150613_135746_zpssaezxvaf.jpg (http://s65.photobucket.com/user/HornetB/media/Rust%20bluing%20Weatherby/20150613_135746_zpssaezxvaf.jpg.html)

[Anorak Bob]

Now Bob and Hornet,

How about a recipe for blackening brass? :)

Bob.

PS Hornet, any chance of expanding a bit on the "humid environment"?

[Stustoys]

Hi Hornet,

Is it normal to do the red dot first?
Do you recall how many "repeats" there were?

Stuart

[Hornetb]

Now Bob and Hornet,

How about a recipe for blackening brass? :)

Bob.

PS Hornet, any chance of expanding a bit on the "humid environment"?


I haven't blackened any brass sorry, but it seems that sulphur is a favourable component to achieving this. In fact Birchwood Casey makes a Brass Black solution. I have no idea if it works well or not, as their cold blues are terrible in my experience. I often find recipes for doing these sorts of things from www.finishing.com (http://www.finishing.com)

http://www.finishing.com/1000-1199/1198.shtml

Birchwood casey comments:
http://www.modelboatyard.com/blackening.html

http://www.traditionalfisherman.com/viewtopic.php?f=50&t=8482

The humid environment I use is a plastic box (or my long thin boiling tank with a lid on if it's a gun barrel) in which I put a slightly damp piece of rag in overnight. Works better if the temperature isn't freezing :rolleyes: but if you had somewhere that was a little warm it would be best. I have seen others use a low wattage light bulb to raise the temp slightly and make a warm humid environment. The warmer and more humid the faster it rusts, which depending on your work schedule may or may not work in your favour. If you have it too wet or there are too big a temperature swings you get larger droplets condensing on the steel that can make the rust uneven. It just depends on how important your finish needs to be. On a rifle, I try to make it impecable. But generally, just leaving it works just fine. And to be honest, I could probably just leave it in my shed with all my machine tools, as they seem to try and rust just fine :~ :rolleyes:

In terms of prebought solutions, Birchwood Casey's Plum Brown works well as a rusting solution also (that's all the browning is, neutralised rust). Just boil the part to turn it black (converts the rust from a red oxide to a black oxide). I've got some of this solution but never used it in this fashion, so can't relate first hand experience.

[Hornetb]

Hi Hornet,

Is it normal to do the red dot first?
Do you recall how many "repeats" there were?

Stuart

That was actually the factory red dot. If it wore off I was just going to dot it on again at the end with red automotive acrylic lacquer that I had handy, but I didn't need to. It stayed put just fine.

Repeats on this piece was probably 8-10 cycles. It varies on different parts, and also the depth of colour can vary depending on the exact steel make up. Some goes nice and black, others a smokey gray. I don't know what determines it though or what exact alloys will give what finish. The steel make up on rifles is already chosen.

You will see over the number of cycles that the rust gets less and less (which is exactly what you want and gives it its rust resistant properties). As the exposed sites susseptible to rust get occupied by the black oxide (I think it is ferric or ferrous oxide, ones red the other is black), then there are less sites available to rust next time round.

At some point you decide to stop, it can be handy sometimes to soak it in a gentle alkaline solution like sodium bicarb just to neutralise any residual acid, then as Bob says, soak it in water displacing oil or just oil. I don't heat it but you can I guess.

[Anorak Bob]

Thank you Hornet,

I have tried Birchwood Casey's Brass Black but the results were disappointing hence the question - http://www.woodworkforums.com/showthread.php?t=188840&p=1813411#post1813411

Bob.

[Hornetb]

Thank you Hornet,

I have tried Birchwood Casey's Brass Black but the results were disappointing hence the question - http://www.woodworkforums.com/showthread.php?t=188840&p=1813411#post1813411

Bob.

Ah Ok.

Sorry it didn't work out for you. As I alluded to, generally I've found Birchwood Caseys stuff works crap to the point of being misleading and falsely represented. The truoil is ok though, but is a lacquer/varnish more than an oil. The cold blues are pretty pathetic.

However, I will say from your post that metho is crap as a degreaser, not sure if that is the cause of your poor results. Acetone far out performs it, and at a pinch lacquer thinners also works ok. Just use the acetone in a well ventilated area. Generally these sorts of things rely on impeccable cleanliness and degreasing.

Another thing I have observed is that generally ANY advise that comes over the counter of a gun shop is worth about 5/8th of FA. :U

If you find something that works I'd be interested to hear also. And like you, I've found it difficult to source straight ammonia.

[BobL]

However, I will say from your post that metho is crap as a degreaser, not sure if that is the cause of your poor results. Acetone far out performs it, and at a pinch lacquer thinners also works ok. Just use the acetone in a well ventilated area. Generally these sorts of things rely on impeccable cleanliness and degreasing..
I agree about metho being a poor degreaser. The way it is made is not that clean. Isopropyl alcohol can be obtained in a fairly pure state and is in some ways a better cleaner and it is also safer than acetone. The best degreaser I've found is dichorlomethane but that can be quite hard to get. I have access to all these chemicals but my preference is for IPA simply because I can now get a lot of it.


If you find something that works I'd be interested to hear also. And like you, I've found it difficult to source straight ammonia.
It's quite easy to make pure ammonia from cloudy ammonia by room temperature vapour transfer.
To do this you need a way of connecting two PE bottle necks together so that it is as gas tight as possible. (black poly elbow and fittings plus heap of teflon tape usually does it).
Completely gas tight is bad as it may then explode. In one bottle place some distilled water and wrap that bottle in al-foil inside an oven bag.
http://www.woodworkforums.com/attachment.php?attachmentid=354201&stc=1
In the other bottle place some cloudy ammonia and warm that side using an incandescent light globe dangled above the cloudy ammonia container or just leave it for a week.
Eventually the NH3 concentration will equilibrate between both sides.
Repeatedly changing the source will slowly increase the concentration of the NH3 in the receiver.
I have managed to get the water very close to the ammonia concentration in the cloudy ammonia side using this method


Pull them out and blow the water off with the air compressor to stop more flash rusting. The rub down with a fine carding wheel (from Brownells) or DEGREASED 0000 steel wool.
A source of oil contamination I found was air from the compressor so the only time I use the compressor is at the end of the last rust stage.
I just let them air dry when I pull them out of the boiling water as I found it doesn't matter if they develop a bit of rust in the middle of the rusting cycles as this will be converted in the next cycle anyway.

[Anorak Bob]

Thanks Bob,

Back when you initially described the process, I had looked online for some laboratory fittings thinking that was the easiest route and then I asked my daughter's boyfriend if he could scrounge some ammonia from his father's industrial cleaning products factory. The Melbourne - Perth thing made it all too hard and that idea fizzed out. Your diagram makes it look very simple. I'm enthused again.

How about this for isopropyl alcohol? - http://shop.coles.com.au/online/national/isocol-antiseptic-rubbing-alcohol

BT

[Hornetb]

A source of oil contamination I found was air from the compressor so the only time I use the compressor is at the end of the last rust stage.
I just let them air dry when I pull them out of the boiling water as I found it doesn't matter if they develop a bit of rust in the middle of the rusting cycles as this will be converted in the next cycle anyway.

Yes, that is a fair point. Contamination is your enemy. To be honest I have probably only done that more towards the end of the process.

When I actually blow with compressed air it is usually when I'm doing a rifle barrel and I do it mainly to clear water from the rifle bore as that is my biggest concern with rust and I dont want that rusting at all. A lot of people plug the ends of the barrel with wooden dowels to keep the water out, but I'm nervous to leave it locked up for the week it takes to blue. You can coat the bore with lacquer and then use lacquer thinner to clean it out at the end too. This of course relates mainly to firearms.

I do plan to set up a hot bluing set up, but this is another level of danger with boiling hot sodium hydroxide and potassium nitrate just for added fun. But the process is much quicker and easier, but the consequences a lot nastier.

[BobL]

Thanks Bob,

Back when you initially described the process, I had looked online for some laboratory fittings thinking that was the easiest route and then I asked my daughter's boyfriend if he could scrounge some ammonia from his father's industrial cleaning products factory. The Melbourne - Perth thing made it all too hard and that idea fizzed out. Your diagram makes it look very simple. I'm enthused again.

Great.



How about this for isopropyl alcohol? - http://shop.coles.com.au/online/national/isocol-antiseptic-rubbing-alcohol

To prevent skin dehydration on sensitive skin that rubbing alcohol is diluted to 640 ml of IPA per litre, so the question is what is it diluted with? I reckon it will be some sort of other evaporative organic - so overall not good.
What you need is 100% IPA like this http://www.isocol.com.au/products/isopropyl-alcohol also available in a Diggers brand at bunny

[BobL]

Yes, that is a fair point. Contamination is your enemy. To be honest I have probably only done that more towards the end of the process..
Yeah the first couple of things I tried were quite patchy. Then I started using gloves and double rinsing and things improved. I should have know better as I worked for many years in an ultra clean laboratory where we went to extremes to minimise contamination.


When I actually blow with compressed air it is usually when I'm doing a rifle barrel and I do it mainly to clear water from the rifle bore as that is my biggest concern with rust and I dont want that rusting at all. A lot of people plug the ends of the barrel with wooden dowels to keep the water out, but I'm nervous to leave it locked up for the week it takes to blue. You can coat the bore with lacquer and then use lacquer thinner to clean it out at the end too. This of course relates mainly to firearms.
I can understand that


I do plan to set up a hot bluing set up, but this is another level of danger with boiling hot sodium hydroxide and potassium nitrate just for added fun. But the process is much quicker and easier, but the consequences a lot nastier.

Folks on here will know I am up for most things but my small scale, relatively slow, needs don't warrant the risks that come with hot bluing.
I don't mind the process being slow as I have many other projects on the go and things to do in between the steps of the fuming cycles.

[eskimo]

Bobl and Hornetb
Why do you your methods over the manganese phosphate ie Parkerising method

[BobL]

Bobl and Hornetb
Why do you your methods over the manganese phosphate ie Parkerising method

My understanding of Parkerising is that it is quicker and provides a stronger more robust coating than the oxides, but the process (especially the manganese version) is trickier.
There are many recipes with many variations and additives and getting it right is not as straight forward as it seems. Nevertheless, as evident in various firearms forums etc, there are many DIYers having a go with it - just how effective these DIT coatings are I have no idea.

My main worry with Parkerising is that it involves heating and disposing of large containers of phosphoric acid which I don't find appealing, especially the getting rid of bulk phosphoric acid afterwards makes it a bit of an environmental problem. In the bluing processes the only thing that gets heated and disposed of down the sink is distilled water with a wisp of acid fumes in it. The fuming process uses very little hydrochloric and nitric acid (20 mll of each will do many batches of parts) and there is no disposal required unless you want close up shop and never do any ever again. Bluing acids are also easily disposed of by neutralizing with caustic. The nitrate in nitric acid could be a nuisance but the amounts are so low as to not be a problem.

It's interesting to see that Parkerising processing services are now being set up in third world countries because gaining environmental approval for large scale Parkerising is getting harder to get in first world countries.

There are better Parkerizing processes than the Manganese Phosphate method now available using hydrofluoric acid (i.e. nasty stuff) and zirconium, The best recipes are patented and the methods are probably outside most DIY user . If I had access to a decent chemistry lab including a way of disposing of the acids afterwards I would give it a go.

[EDIT] I had a bit of a read of a couple of Patents for the Fluoro Zirconic Acid method and here is a typical list of ingredients






Chromic Acid Flake


CrF3—4H2O


CrOHSO4 35%


Phosphoric Acid 75%


Thickener


Surfactant


Fluorozirconic Acid,


Liquid Caustic Potash
DIstilled water

[Stustoys]

hydrochloric acid (battery acid)

Make up your mind ;) Isn't battery acid sulfuric?

Would there be a best before or use by date on a bottle of this once mixed?

Hi Bob,

Whats the Aluminium foil for in your vapour transfer setup?

Stuart

[BobL]

Make up your mind ;) Isn't battery acid sulfuric?
Correct


Would there be a best before or use by date on a bottle of this once mixed?
It should last for quite a while if its kept in an air tight container.


Hi Bob,
Hi Stu.


Whats the Aluminium foil for in your vapour transfer setup?

It reflects heat away from the receiver - I forgot to add the light globe..

The arrangement below is better as it concentrates the warmth on the ammonia feed.
We controlled the ammonia transfer using a light dimmer on the light globe.
No heat required a week or so to get a reasonable amount of ammonia into the water - with heat the time it took depended on how much heat was used.
We used clear teflon PFA 500 ml bottles and back then they cost about $50 each and a teflon connection.
Because the bottles were teflon we could crank the light globe up and we even used a 150W infra red lamp but this is not possible with PE or it would melt.
It is possible to purify small amounts of acid like this as well - no water is needed in the receiver
http://www.woodworkforums.com/attachment.php?attachmentid=354353&stc=1

[Hornetb]

Make up your mind ;) Isn't battery acid sulfuric?

Stuart

You're right actually :roll:. Brain fade moment.

Not sure where I got the hydrochloric from now, I have about 4L of the stuff.

[Stustoys]

Correct

Am I correct in assuming sulfuric acid isn't an alternate for Hydrochloric acid?




It reflects heat away from the receiver


That was my guess at what you were doing. I like plan B much better.

Thank you

Stuart

[Stustoys]

You're right actually :roll:..
Dont worry I wont make a habit of it :wink:

[BobL]

Am I correct in assuming sulfuric acid isn't an alternate for Hydrochloric acid?

That was my guess at what you were doing. I like plan B much better.

Thank you

Stuart

My understanding of black oxide methods is that an oxidising acid is needed to make the surface rust.
This is why nitric or sulphuric are required.
The HCl is a sort of catalyst to help speed up. the process

[wheelinround]

:2tsup:

[Vernonv]

Thank you for the write up ... I do find this subject very interesting, although I've only ever done Parkerizing (with mixed success).

One question I have is why does the rust go black when boiled in distilled water? Is it actually changing from "rust" into something else?

[BobL]

Thank you for the write up ... I do find this subject very interesting, although I've only ever done Parkerizing (with mixed success).

One question I have is why does the rust go black when boiled in distilled water? Is it actually changing from "rust" into something else?

Rust is a mixture of red ferric oxide (Fe2O3) and water.
The boiling distilled water converts some the red oxide to the ferrous (black) oxide or FeO.
The final combination of FeO and Fe2O3 is called black rust or magnetite (Fe3O4)
Magnetite is moderately more protective against rust than plain iron and especially but it wear off and will still eventually convert to rust.

[Stustoys]

and especially
What Bob, You've got me on the edge of my seat :D

Stuart

[BobL]

What Bob, You've got me on the edge of my seat :D

Stuart

regular orange rust, ie "rust does not protect against rust"

I can't believe you blokes are paying that much attention - I'd better be careful what I . . . . . .

[Stustoys]

Sorry Bob I must be thicker than usual tonight :no:

"Magnetite is moderately more protective against rust than plain iron and especially but it wear off and will still eventually convert to rust."

"Magnetite is moderately more protective against rust than "regular orange rust" and especially but it wear off and will still eventually convert to rust."

Still not getting it :(

Paying attention because I want to try it. You know who's getting the blame if it doesn't work ;)


Stuart

[eskimo]

Sorry Bob I must be thicker than usual tonight :no:

"Magnetite is moderately more protective against rust than plain iron and especially but it wear off and will still eventually convert to rust."

"Magnetite is moderately more protective against rust than "regular orange rust" and especially but it wear off and will still eventually convert to rust."

Still not getting it :(

Paying attention because I want to try it. You know who's getting the blame if it doesn't work ;)


Stuart

you might be thick so i must be jungle thick n dense

when you figure out the vest way Stuart let me know...:D

[BobL]

OK There are a number of possibilities to start with to guard against a (red/orange) rusted object form more rusting.

1) remove old rust i.e. get back to Plain-raw iron

2) Leave the iron rusty with orange/red oxide

3) convert the rrusty with orange/red oxide to black oxide

4) coatings and other conversions

etc

Of the first three, 3) is much better than the other two and the least effective is to leave the rust there - a rusted object has a greater surface area exposed and being more porous stays wet for longer hence rusts quicker than removing the rust and getting back to a flat dry surface.

[Michael G]

So Bob, if you just boiled a red/orange rusted item in distilled water, would that be enough to convert to black rust? (as per post 28).
From what I've read so far it seems to me that the the fuming is to establish a uniform coat of rust on the steel, so if it is there already?
Michael

[BobL]

So Bob, if you just boiled a red/orange rusted item in distilled water, would that be enough to convert to black rust? (as per post 28).
From what I've read so far it seems to me that the the fuming is to establish a uniform coat of rust on the steel, so if it is there already?
Michael

You are correct about the fuming being to establish a uniform coat of rust on the steel - but as important is that it is a THIN and smooth coating bonded to the base metal.
Only a thin outer layer of red rust is converted by the boiling, so if the red rust layer is too thick it won't convert and it leaves a irregular layer of black oxide over the remaining unconverted rust which is porous and relatively un-protective.

Remember once the water converts the outer layers of red to black oxide you end up rubbing most (99%) of the black oxide off so only the layer bonded closest to the metal remains. If that layer is not bonded to the metal it will bonded to underlaying red rust which is not a strong bond and will come off - if not now then later.

Best (i.e. longest lasting) results are obtained with the smoothest surfaces since this can produce the thinnest layers.

It's tempting to let the fumes rust the metal for longer to form thicker coatings of red rust.
When I have done this the result was a thicker patchy layer of rust and resulting soot most of which come off but leaves a more patchy finish - more, shorter exposures, will be better than a fewer longer fuming exposures.

When the weather is hot a 4-6 hour fume exposure is plenty. when its colder I use 8-10 hours. The worst finish was when I accidentally left something for 24 hours and the resulting coating was rough and irregular. If this happens early the resulting top layers will get increasingly rougher. If it happens in the second last or last pass it will still be protective but just may not look as as good.
If this happens in the first 3-4 passes I recommend going back to bare metal and starting again

In general the coatings on scotchbrite (matt) finished steel have not been as good as buffed to a mirror finish steel.

[BobL]

Here's some pics after the final pass (9 passes in all) through the fuming tank and a bath in warm engine oil..
The final pass included an accidental 24 hour fume in the fuming tank.
This has resulted in a rougher finish but I'm not that concerned about these pieces having a real fancy finish as long as they are reasonably well protected.

Photographic black things at night is difficult at the best of times but it is what it is.

This is with led fluoro lighting - it's hard to see much on these surfaces as they are too dark.
The glint you can see is a tiny bit of remaining oil
http://www.woodworkforums.com/attachment.php?attachmentid=354490&stc=1

Now with flash only
You can see a bit clearer that they have a matt finish
http://www.woodworkforums.com/attachment.php?attachmentid=354491&stc=1

Here are the pieces all assembled into the bearing housing.
For comparison the surrounding steel has two coats of matt epoxy-enamel black
http://www.woodworkforums.com/attachment.php?attachmentid=354492&stc=1

In this one I have pushed the exposure in Photoshop so you can more easily .see the rougher texture on the edges - its nowhere near as bad as it looks
http://www.woodworkforums.com/attachment.php?attachmentid=354493&stc=1

For comparison purposes here is the bluing of the small rotary table mounting plate and tool post I made a year or so back.
This had 10 passes though the tank.
http://www.woodworkforums.com/attachment.php?attachmentid=216239&stc=1&d=1342615982

.

[WoodBee2]

You are correct about the fuming being to establish a uniform coat of rust on the steel - but as important is that it is a THIN and smooth coating bonded to the base metal.
Only a thin outer layer of red rust is converted by the boiling, so if the red rust layer is too thick it won't convert and it leaves a irregular layer of black oxide over the remaining unconverted rust which is porous and relatively un-protective.


I read all this information with great interest, and you seem to know a lot about it. You are undoubtedly right about more thin layers instead of one thick, but I can't understand what happens when you repeat the fuming/boiling several times. Wouldn't that form a thick layer also? (be it more uniform) that would be polished off? Reading the previous posts I assume not, but can you explain what happens?

Peter

[BobL]

I read all this information with great interest, and you seem to know a lot about it.
Don't be fooled by appearances. I have undertaken the process ~7 times in ~3 years and during that time blued/blackened maybe ~30 pieces.
What I do know something about is inorganic chemistry as it used to be part of my day job but I'm not a corrosion expert.
Corrosion science is very specialised and as complicated as or maybe more complicated than metallurgy.
However, I can read and mostly understand scientific papers on corrosion.


You are undoubtedly right about more thin layers instead of one thick, but I can't understand what happens when you repeat the fuming/boiling several times. Wouldn't that form a thick layer also? (be it more uniform) that would be polished off? Reading the previous posts I assume not, but can you explain what happens?

The soot formation only forms where there is red rust.

However, the red rust layer formed is not uniform either, instead it consists of a very thin layer over most of the metal and then patches of mounds, lumps, bumps and other structures most of which are fragile and porous. Provided all these red rust structures are thin enough they will be converted to black oxide but the fragile rust also becomes the soot which must be rubbed off to allow the fumes to get access to the untreated metal underneath.

The soot comes off easily but the very thin layer of black oxide that is hard bonded to the metal and to itself is much harder to remove. In the first couple of passes, after removal of the soot the amount of black oxide that remains hard bonded to the metal is so thin and so sparse that the metal may only look like a dark grey.

*********************************************************************

If you want to know more read on
OK lets take a step back and try to understand rusting.

The simple view about rust formation is that air (oxygen) attacks the surface directly and eats holes in metal.
Iron that has been kept away from water (including any condensation from humid air) can stay rust free for years and when it does rust it does not rust anywhere near fast forming a smooth layer - this is rare because there is always water in the atmosphere.

What really speeds up corrosion is water, even the small amount in dry air is enough. When water droplets condense on cold iron the water already has dissolved oxygen in it and this is much more reactive than oxygen gas in the air. The dissolved O attacks the iron more on some places on the iron surface than others and forms an iron rich solution in the water drop.
When the iron oxidises into the water it releases electrons into the metal which move to other local parts of the metal forming a slightly reducing environment in that area which pulls some of the iron out of the water droplet. This is why you get pitting, on some parts of the metal surface and in others you get mounds.

This is a picture of bare steel left outside out of the rain - note the patchiness of the rust.

http://www.woodworkforums.com/attachment.php?attachmentid=354513&stc=1

Here is a schematic rom http://chemwiki.ucdavis.edu/Analytical_Chemistry/Electrochemistry/Case_Studies/Corrosion of what happens
http://www.woodworkforums.com/attachment.php?attachmentid=354512&stc=1
Because of the water, and that oxygen from the air can continually dissolve into the water, the small amount of reduced iron also deposits large variable amounts of iron oxides and water (embedded in the solid structure) which is what rust is and that is why it is rarely a uniform colour. It's not really a well defined material and is not considered a material at all in a chemical sense, instead it's considered a solid mixture. The deposit is loosely bound to the metal and unlike some other metal oxide layers does not form a barrier against further corrosion at this is why rust is so friable.

Now what you don't want with metal bluing is any visible pitting or for the layer of rust to build up into large lumps which is happens when the metal is exposed to the acids for too long.
You want the pits and the deposition spots to be so tiny as to be to be invisible and so all the red iron oxides to be converted to the black iron oxides. If the lumps are too big the red oxides will not be converted into black oxides and the surface will not be as strong as a solid black oxide only layer. What happens after boiling and when the soot is removed is you can reduce the high points but the pits generally retain some soot which is not desirable.

I have never hear of this but I reckon that the brown hues sometimes seen during metal bluing is due to incomplete reduction of the red to the black rust. A very small amount of red rust inside the black rust can probably be tolerated.

In my last pass on the parts I blued in this thread I did leave the parts too long in the fuming chamber and there were larger patches of rust formed.
To show this effect I pushed the exposure in Photoshop in the picture below to show the speckled outer edges of these discs.
The highllghts you see are not shiny metal but the polished tops of the converted or black oxide mounds that are reflecting the flash compared to the surrounding darker areas.

This is why if you want a smooth finish, starting with mirror finish is essential because it's all downhill from then on.

http://www.woodworkforums.com/attachment.php?attachmentid=354516&stc=1

[WoodBee2]

Hi Bob,
I have been on holiday for a while, but have just read your thorough but understandable (to me) explanation. Thank you very much for the effort to write this all down!

Peter

[Stustoys]

For Concentrated HCl I used Diggers Spiirts of Salts from Bunnings.
Nitric acid is not so easy to get but Sulphuric acid can be substituted for nitric..

Diluter forms will also work but take longer although some reduction in time can be achieved by then using a smaller chamber/

Hi Bob,

Bunnings dont seem to have Diggers anymore. They have Chemtech brick and tile cleaner, 95g/L Sulfamic acid and 53g/L Hydrochloric acid. Is that acceptable?

Thank you.

Stuart

p.s. the funny thing is I have a blacking kit in the shed I havent even tried yet

[BobL]

Hi Bob,

Bunnings dont seem to have Diggers anymore. They have Chemtech brick and tile cleaner, 95g/L Sulfamic acid and 53g/L Hydrochloric acid. Is that acceptable?

Thank you.

Stuart

p.s. the funny thing is I have a blacking kit in the shed I havent even tried yet

Sulfamic is probably not oxidising enough.

What about this mob.
http://www.anpros.com.au/contact-us/

[Stustoys]

Sulfamic is probably not oxidising enough.

What about this mob.
http://www.anpros.com.au/contact-us/

Considering they're about a 10 minute walk from my place they will do just nicely. Thank you.
Don't they have lots of nice stuff! Though it is tempting to buy everything 2.5L at a time :( (which granted would be more then a little silly)

Stuart

[BobL]

Considering they're about a 10 minute walk from my place they will do just nicely. Thank you.
Don't they have lots of nice stuff! Though it is tempting to buy everything 2.5L at a time :( (which granted would be more then a little silly)

Stuart

It's not worth keeping large amounts of nasty stuff in a domestic environment. Before we had an accountable acid disposal system at Uni I acquired a 20L carboy of used high purity aqua-regia. When I say used it was used, it had been used for cleaning labware that was already way cleaner than would be the case in most labs. It was going to be disposed of so I grabbed it. I used some of it in a plastic bucket to dissolve Zinc plating off some steel pipe - veritable little volcano that turned out to be leaving a 5ft clean ring of brickwork on the back pergola paving. When the black plastic 20L carboy started to blister I got worried and I didn't want to keep it in the shed or under the house for obvious reasons so it lived on the back veranda for a while - bit of risk when kids came over to play. I did some steel etching with it - nothing fancy and not that good either. With summer coming I transferred half a litre to an FEP teflon container and used the rest to clean the remainder of the pergola and driveway brick paving. It worked great - killed all the weeds, moss etc and nothing grew in between the bricks for a couple of years.