Thread: Restoring Metal objects and surfaces

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

Thank you Bob.

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.

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

Originally Posted by Master Splinter

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.

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))


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.

BobL

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

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

Ken

Originally Posted by neksmerj

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.

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

Originally Posted by 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.

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 https://www.woodworkforums.com/showth...44#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.

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.

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)

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.


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.





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.



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.

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
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.
Rob.

Originally Posted by 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
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.
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

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.

Originally Posted by 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.

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.