Restoring Metal objects and surfaces

[BobL]

While looking around on the web for a tannic acid based rust converter recipe for ferrous preservation I stumbled across the Canadian Conservation Institute website.

They have a site dedicated to links to PDFs on the preservation of a wide range of materials including metals.
The focus is on authentic preservation for a museums environment but there are lots of goo ideas there for general use.

see


Metals

N9/1 Recognizing Active Corrosion (2007) (https://www.cci-icc.gc.ca/resources-ressources/ccinotesicc/9-1-eng.aspx) (PDF Version, 2.01 MB)
N9/2 Storage of Metals (2007) (https://www.cci-icc.gc.ca/resources-ressources/ccinotesicc/9-2-eng.aspx) (PDF Version, 166 KB)
N9/3 The Cleaning, Polishing and Protective Waxing of Brass and Copper (2007) (https://www.cci-icc.gc.ca/resources-ressources/ccinotesicc/9-3-eng.aspx) (PDF Version, 163 KB)
N9/4 Basic Care of Coins, Medals and Medallic Art (2007) (https://www.cci-icc.gc.ca/resources-ressources/ccinotesicc/9-4-eng.aspx) (PDF Version, 161 KB)
N9/5 Tannic Acid Coating for Rusted Iron Artifacts, formerly published under the title Tannic Acid Treatment (2013) (https://www.cci-icc.gc.ca/resources-ressources/ccinotesicc/9-5-eng.aspx)
N9/6 Care and Cleaning of Iron (2007) (https://www.cci-icc.gc.ca/resources-ressources/ccinotesicc/9-6-eng.aspx) (PDF Version, 157 KB)
N9/7 Silver - Care and Tarnish Removal (2007) (https://www.cci-icc.gc.ca/resources-ressources/ccinotesicc/9-7-eng.aspx) (PDF Version, 265 KB)
N9/8 Mechanical Removal of Rust from Machined Ferrous Surfaces (2007) (https://www.cci-icc.gc.ca/resources-ressources/ccinotesicc/9-8-eng.aspx) (PDF Version, 227 KB)
N9/9 Care of Objects Made of Zinc (2007) (https://www.cci-icc.gc.ca/resources-ressources/ccinotesicc/9-9-eng.aspx) (PDF Version, 146 KB)


I'm going to give their tannic acid coating recipe (N9/5) a go.
Last year I used commercial tannic acid rust converter on a Band saw mill and I am really pleased at how it has worked out even when left outside.
The problem with the commercial converter is it costs a bomb and the recipe provided in the above link ends up working out at less than 1/10th of the commercial price.

[KBs PensNmore]

Thanks Bob, some interesting reading there. Now to find an old piece of machinery to use that information on.:D
Kryn

[Anorak Bob]

Thank you Bob.:2tsup:

I just sent a copy of the links to my eldest daughter. I am certain she will find them and the information they contain useful, as will I.

Bob.

[Master Splinter]

Thanks! I've always liked the commercial tannic acid treatments, but disliked the sucker pricing it attracts!

[BobL]

Thanks! I've always liked the commercial tannic acid treatments, but disliked the sucker pricing it attracts!

I'm looking at purchasing a bulk amount (1 kg) of Tannic acid powder which will make up to 40L of working solution.

It's not a simple dissolve and dilute process, i.e. pH needs to be measured and adjusted with some phosphoric acid etc . . . .

When I finally make up the concentrated form, if anyone in the Perth area wants some at cost I would be happy to provide it.

Compare that with something like Fertan which costs more than $50/L for working strength solution.

PM me if you are interested.

[BobL]

After the usual amount of stuffing around and not being able to find any non-food-grade tannic acid I ended up buying a kilogram of food grade tannic acid from a wine and brewing supply company, The food grade stuff cost almost double the price of the non-food-grade material but still works out way cheaper per litre than commercial products like Fertan.

The preparation process
N9/5 Tannic Acid Coating for Rusted Iron Artifacts, formerly published under the title Tannic Acid Treatment (2013) (https://www.cci-icc.gc.ca/resources-ressources/ccinotesicc/9-5-eng.aspx))


is not too bad just a bit messy.

Luckily over the years I have acquired some chemical prep gear and the aquarium pH meter came in useful seeing as we no longer have one.
I mixed the 900 g of deionised water, 100g of tannic acid and 50 g of alcohol in a pyrex jug and heated that on low heat on an electric frypan.
The resulting ugly looking very dark brown liquid had a pH of 3.9.
The recipe then calls for addition of dilute (10:1) H3PO4 to decrease the pH of the solution to between 2.2 and 2.4 apparently so that it works better as a rust preventer.
The recipe suggests that around 2 -3 mL of dilute acid might be required.
I did the chemical maths and it did not seem like that would not be enough H3PO4 and sure enough after adding 10mL of the dilute acid the pH had only shifted from 3.9 down to about 3.5 so I added the concentrated acid direct with a small plastic pipette and managed to get the pH to 2.3 pretty easily.
This is stored in a fridge - the ugly colour should act as a deterrent against anyone drinking it but it is boldly labelled as well.

This solution is then diluted 3:1 to form the working solution.

First cab off the rank for rust treatment will be a small, not too badly rusted, swage block I picked up last week. I've had my eye on swage blocks for a year or so but they were all either too big, too beat up ,or too expensive - not that this one was cheap or in prime condition. Will post some pics in the smithy forum later.

[neksmerj]

BobL

Have you had any success with the tannic acid treatment of steel?

If yes, what's the black colour like, pictures?

Ken

[BobL]

BobL

Have you had any success with the tannic acid treatment of steel?

If yes, what's the black colour like, pictures?

Ken

Hi Ken,

I need to dilute the brew I made down and pH balance it again before I can use it. Then I will run some tests and post pics and the results.

I have used FERTAN which is commercial tannic acid solution by Chemtec.
FERTAN is good at converting the rust to a fine black powder. Like mine will, FERTAN requires multiple applications to complete the rust conversion. However, unlike Phosphoric acid conversion tannic acid dries quickly and thoroughly. Most of the times I have used phosphoric it has taken a long time to dry and it even when dry when the air becomes humid the surface become sticky.

The tannic acid finish is not that strong mechanically, it tends to be loosely bonded and somewhat powdery and does eventually come off - it also rubs of and stains stuff so it is a bit of a nuisance,.
It's not the best method for something that you want to leave black that has to be handled, I'd go for something else in that case.

The idea of both the phosphoric and the tannic treatments is not as a final finish but something to convert the rust and then last long enough until you can get a more protective finish onto the surface.
If you want to you can brush the blackened tannin surface with a stiff brush to clear the loose stuff prior to painting but it is not essential as paint bonds nicely through the loose stuff.

[neksmerj]

Hi BobL

I was under the false impression that the tannin acid finish would result in a nice black surface, however, it seems I'm mistaken.

Have you had any success with a home brew solution for blackening steel?

I've tried some commercial blackening kits with mixed results. I get a good colour, however the finish rubs off, not ideal.

Tis a pity there isn't a similar process for steel as anodising is for aluminium.

Ken

[BobL]

Hi BobL
I was under the false impression that the tannin acid finish would result in a nice black surface, however, it seems I'm mistaken.

Looks wise it is quite a nice finish, but it is not mechanically strong nor one that can be handled, it stains your hands.
I use electrolysis for rest removal on small items but that doesn't help on items don't fit in the tank - I wanted something I could use insitu that I was going to eventually paint.


Have you had any success with a home brew solution for blackening steel?
I've tried some commercial blackening kits with mixed results. I get a good colour, however the finish rubs off, not ideal.
Tis a pity there isn't a similar process for steel as anodising is for aluminium.
Ken

I've done some traditional metal bluing/blacking - it produces a great finish that is thin and strong.
Unfortunately it doesn't cope with handling over a long period
eg http://www.woodworkforums.com/showthread.php?t=152165&p=1522244#post1522244

The downside is that it takes a long tine to get this - it took me 15 minutes every couple of days over two weeks to get that finish - I could probably reduce that to about a week of 10 minutes a day.

[BobL]

I finally diluted the Tannic acid to working strength and balanced the pH and did some trials.

The recommend treatment is 3 coats of dilute Tannic acid (TA) and I compared it to a single coat of commercial Phosphoric Acid (PA) based rust converter.

Firstly some heavily rusted railway track plates.
These have been many weeks under seawater and then left in a pile to rust
Before any treatment they look like this.
http://www.woodworkforums.com/attachment.php?attachmentid=348249&stc=1
I don't think either TA or PA are really intended to tackle this degree of corrosion

After 3 coats of TA (LHS) and 1 coat of PA (RHS)
http://www.woodworkforums.com/attachment.php?attachmentid=348248&stc=1
The TA found it hard to wet the surface and tended to run off so I had to work it into the rust.
The PA has some detergent in it which really helps wet the surface but doesn't help it dry, but then again neither does pure PA anyway.
I think there is a bit of other stuff on the steel besides rust, the PA bubbled furiously for a bt when first applied indicating carbonate deposits
The TA takes about 2 hours to dry and then I reapplied it twice more. After about 8 hours the PA is still tacky and lumpier.
In humid weather sometimes the PA stays tacky for days so I put in in a BBQ oven to dry out - this works but is just a PITA
Neither TA or PA appear to have fully converted the rust but then again this is not really the intended target for these converters

Now some lightly rusted steel
This is after one coat of TA and one of PA
There is still some rust under the the TA - this is why it needs 2 coats.
http://www.woodworkforums.com/attachment.php?attachmentid=348252&stc=1

This is after 3 coats of TA, the PA is still slightly tacky.
The TA appears to have completed the conversion but another coat would probably be worth applying.
The TA coating is smoother than it looks
As expected some of the dry ferric tannate (black stuff) rubs off it it is touched.
The instructions say brush loose stuff off and paint over the top.
http://www.woodworkforums.com/attachment.php?attachmentid=348251&stc=1




Now some bare steel plates - sorry its dark and I had to use flash.
The upper piece is the other side of the piece used above with the rust taken off with a Scotchbrite wheel.
This still leaves the blue oxide finish originally on the steel when purchased on the steel
TA (LHS) and PA (RHS) are painted over the top of the blue oxide.
Once again 3 coats of TA and one of PA

Lower piece has been sanded back to bare metal
The TA (LHS) leaves a much smoother finish with a mostly blue appearance compared to the PA (RHS) which leaves a blue black lumpy finish.

http://www.woodworkforums.com/attachment.php?attachmentid=348250&stc=1

Now I will leave these outside of the next few months and see what happens.
TA alone is not intended for pieces that are going to be handled or for long term outside.

One question some of you may wish to know is how does it compare to a commercial product like Fertan?
I think Fertan may be a bit more concentrated than the home brew but it still requires multiple applications to work properly.

Already I can see the home brew TA is as good as Fertan for light rust conversion.

The sorts of uses I have in mind are
While doing a MW project - TA is painted on pieces to keep the rust off until I can paint.
Following electrolysis, paint on some TA to prevent re-rusting
General light to medium rust conversion on hard to get at places and pieces too big for electrolysis.

There is a fair bit of mucking around preparing the solutions but in terms of hard $ it's costing me around $2.50 a litre to make the home brew so I'm pretty happy about this.
The other thing is that the TA powder used in this home brew is Food-Grade and even though it contains 10-15 drops/L of concentrated PA it's much safer to deal with than raw PA rust converter. You could probably drink a bit and it would not kill you although it will taste like the roughest wine you will have every tasted.
Unfortunately it's still messy and stains clothing and raw wood so you can't really carelessly spray it around without making a mess.

[Ropetangler]

Thanks Bob for your considerable body of work here. It makes most interesting reading. I had never even heard of Fertan before reading this thread, so have never tried it. I usually use Ranex H3PO4 based product, or electrolysis, and I have 2 ways of using the phosphoric acid based rust converter.
It can be used as directed, painted over rusty areas, which turn black as they dry and can then be painted over, - everyone would be familiar with that. I also use it on items like machined surfaces, - a shaper table is one example, where I first used a carbide tipped scraper, (of the kind used for scraping machined ways, or straight edges) to remove most of the relatively loose rust, and then using a Scotchbrite pad soaked in straight Ranex to rub the remaining rust away, leaving a surface with a freshly machined appearance. It did take plenty of elbow grease however, but the result was excellent. To finish I wiped down with a damp cloth, dried it off and sprayed a coat of Lanotec on for ongoing protection.
Just a quick note on using the scraper. I kept the angle of attack low, and the rust alone was removed, but virtually no cast iron. That was on a machined surface, it would not be the same for an unmachined item. With a machined surface even a single edged razor blade would take the rust away without marring the surface, but not for as long as a carbide scraper:wink:
I haven't found that Ranex is particularly nasty to handle, While I do wear rubber gloves, I have had the odd splash on bare skin, it is nothing like conc.H2SO4 or HNO3 as regard to stripping flesh from those who are careless.:o
Rob.

[BobL]

Thanks Bob for your considerable body of work here. It makes most interesting reading. I had never even heard of Fertan before reading this thread, so have never tried it. I usually use Ranex H3PO4 based product, or electrolysis, and I have 2 ways of using the phosphoric acid based rust converter.
It can be used as directed, painted over rusty areas, which turn black as they dry and can then be painted over, - everyone would be familiar with that. I also use it on items like machined surfaces, - a shaper table is one example, where I first used a carbide tipped scraper, (of the kind used for scraping machined ways, or straight edges) to remove most of the relatively loose rust, and then using a Scotchbrite pad soaked in straight Ranex to rub the remaining rust away, leaving a surface with a freshly machined appearance. It did take plenty of elbow grease however, but the result was excellent. To finish I wiped down with a damp cloth, dried it off and sprayed a coat of Lanotec on for ongoing protection.
Just a quick note on using the scraper. I kept the angle of attack low, and the rust alone was removed, but virtually no cast iron. That was on a machined surface, it would not be the same for an unmachined item. With a machined surface even a single edged razor blade would take the rust away without marring the surface, but not for as long as a carbide scraper:wink:
I haven't found that Ranex is particularly nasty to handle, While I do wear rubber gloves, I have had the odd splash on bare skin, it is nothing like conc.H2SO4 or HNO3 as regard to stripping flesh from those who are careless.:o
Rob.

Thanks Rob.
While it's far from perfect I would use Fertan over H3PO4 for most situations.
The main disadvantage up until now has been the cost of of TA based converters like Fertan. Given that I can now make TA for about 1/10th of the cost of H3PO4 based converters I won't be using H3PO4 again. Well that is not correct because a few drops of H3PO4 is needed to pH balance the TA. Hopefully the 300 mL or so I have left of H3PO4 will last me for a while.

BTW if you still want to keep using H3PO4 based converters I found the Chemtec H3PO4 is a bit cheaper and more concentrated than Ranex.
Ranex says it is between 30 and 60% than H3PO4 R whereas the CHemtec is 65% H3PO4

[Ropetangler]

Thanks for the tip Bob, but as I have about 3 litres of Ranex (out of 5) left, it will be some time I would expect before I need to replenish stocks. I would offer to send you some to replenish your stock, but I imagine that Australia Post would not be too happy doing the courier work. However if you find yourself on the N.W.coast of Tasmania anytime soon, do get in touch, it would be great to meet another Forumite, and you could take some with you.:) Cheers,
Rob.

[BobL]

Thanks for the tip Bob, but as I have about 3 litres of Ranex (out of 5) left, it will be some time I would expect before I need to replenish stocks. I would offer to send you some to replenish your stock, but I imagine that Australia Post would not be too happy doing the courier work. However if you find yourself on the N.W.coast of Tasmania anytime soon, do get in touch, it would be great to meet another Forumite, and you could take some with you.:) Cheers,
Rob.

Cheers Rob, It could happen that I end up visiting Tassie. SWMBO's cousin, who I am good mates with, recently moved to Launceston and we're scheduled to make a visit there sometime.

[Ropetangler]

Cheers Rob, It could happen that I end up visiting Tassie. SWMBO's cousin, who I am good mates with, recently moved to Launceston and we're scheduled to make a visit there sometime.

We are less than 2 hours drive from Launy, if you don't stop for any of the attractions along the way, (might be easier said than done) so if you can organise a couple of weeks or so, pretty well the minimum to do Tassie justice I would think, it would be great to see you. Only thing is that we are about to head North for a few months, so some time after September might be best for me to be able to show you around my back yard. Now I'm off to the local Community Shed for a few hours to assist our chief bio diesel brewer amongst other duties.
Rob.

[chambezio]

Thanks Bob for a very informative thread. I bought 250ml of Fertan last week and it cost $32. I am going to start a WWII Jeep restoration. I did, a while ago strip all the paint off the front guards and grill. I foolishly just put them aside and of coarse the surfaces have a good but light coat of rust. One thing about the surface rust and its treatment may give the paint a good key. I have at times painted disc sanded steel that was really shiny, but it wasn't long before the paint "fell off".

[BobL]

Thanks Bob for a very informative thread. I bought 250ml of Fertan last week and it cost $32.
Ouch!


I am going to start a WWII Jeep restoration. I did, a while ago strip all the paint off the front guards and grill. I foolishly just put them aside and of coarse the surfaces have a good but light coat of rust. One thing about the surface rust and its treatment may give the paint a good key. I have at times painted disc sanded steel that was really shiny, but it wasn't long before the paint "fell off".

That's also been my experience. The blue oxide coating on standard commercial steel also seems to need some sort of etching.

[BobL]

Here is a full sunlight pic of the two treated surfaces on the sanded metal some 18 hours after application.
It's been a dry night and the PA treated surface has fully dried out and is flaking.
The small shiny patches on the edges of both plates suggest further treatment would be appropriate.

http://www.woodworkforums.com/attachment.php?attachmentid=348262&stc=1

[BobL]

Its some 3 weeks later and I thought I'd post a photo of how this experiment is going.

Just a reminder of how these bars started out
http://www.woodworkforums.com/attachment.php?attachmentid=348250&stc=1

These bars have been left outside under an open veranda where they would have been exposed to some spray from several heavy showers we've had during the exposure period.

Top bar is as supplied from steel merchant, blackened steel plate, TA coating on left and PA on right
Lower bar was sanded back to bare metal, again TA on left and PA on right


http://www.woodworkforums.com/attachment.php?attachmentid=352956&stc=1

It's hard to see on the top plate but there are patches of rust in between the black blotches of the PA application.
Although there is a bit of rust on the TA side on the lower plate the TA appears to be outperforming the PA.

The other thing I notice is that application of both PA and TA onto the black oxide steel bar works better than for bare metal
I suspect that even a light rusting converted to either a tannate or phosphate is more protective than coating the bare metal - so the conclusion here is to let your work rust a tad before conversion

A major advantage of the TA is that it dries to a thin coat so multiple/repeated applications are not going to make anywhere near as much of a mess as repeated PA application. I have started to do that in the shed. As soon as I seen a rust spot somewhere I wipe a tannic acid soaked rag onto that spot. It would also possible to do this for tooling like shanks and bits as the TA coating is so thin in most it will not affect tolerances. One thing to be a aware of is that the TA coating is not physically robust and will rub off so repeated applications are still needed.
I don't have that much of a rust problem on tooling probably because I use lube and just blow clean the tooling before putting it away.