Thread: Darkening cast iron?

If you want a semi rustic look, then heating the handles to near red heat and dunking them in oil will produce a darkened finish. Different oils produce different effects like a slight crackle finish.
This is similar to the conditioning of cast iron saucepans.

Otherwise welcome to the world of metal bluing.
It's called metal bluing but it really only works on metals containing iron.
Even though its called bluing the colours are anywhere from very hard brown, dark grey to blue black to black.
There are two types or processes Cold and Hot bluing
If the handles are to be constantly handled then Hot bluing is needed.

There are many ways to achieve this effect but rather than repeat everything look here ( https://en.wikipedia.org/wiki/Bluing_(steel) ) for a basic summary.

I've done mainly cold fume bluing of ferrous materials.
it's a long painstaking process and does not suit handles that are handled often.
This an example of a tool post and and bracket that I made to support this small rotary table for a metal work lathe.
before
toolpostjpg2.jpg
After
toolpostjpg3f.jpg

This is a bearing/pulley holder - the flat bar/plate that the holder is bolted to is painted Epoxy matt black.
finalass1.jpg

BTW black epoxy enamel probably provides better protection than the cold bluing, maybe even as good as the hot bluing.
It's certainly a lot easier.

What about flax seed oil/baking in an oven as Benchcrafted do for their handwheels?

Originally Posted by FenceFurniture

What about flax seed oil/baking in an oven as Benchcrafted do for their handwheels?

Flax seed oil is the same as raw linseed oil.

A hot oven carbonises the oil and produces a nice black finish. Watch out it makes some smoke
It's the slow version of heat object and dunk into oil method I refer to above although it is much kinder especially on delicate pieces.
Long term it will also eventually wear off.

If you object is too large to heat another method is to blacken the steel using tannic acid and then coating with BLO.
In this case the BLO is just a protective outer later - the coating is not a robust as the hot object in oil or oven method but its better than nothing.

Before and after restoration of a blacksmith vice,
FinalBSvice.jpg

Phosphoric acid?

Originally Posted by Jeffen

Phosphoric acid?

Most commercially available PA sold as rust converter contains detergent to make it wet the surface.
PA works better on pre-rusted surfaces where by it takes up the texture of the rust but on bare metal it does the following (see seetl strip on RHS)
The other is tannic acid.
Both are after one coat of acid, the tannic acid gets darker with successive coatings


ClearMeta2l.jpg

After one week of exposure under a veranda the tannic acid surface had a couple of rust spots while the died up detergent in the PA reabsorbed moisture from the air and had rust over most of the steel surface.

The tannic acid will rub off if handled and then it too will rust so it needs a carbonised oil covering. Museums Canada uses the tannic acids for vintage restoration but only on objects that are not handled.

Birchwood Casey gun bluing is readily available on ebay and the likes. There are some videos on youtube showing how to apply it and the kind of result you'll get. Here's a video on benchcrafted's website from 6 years ago. Benchcrafted Blog

Whoah! Just as an aside. I can't ever recall commenting on a Benchcrafted blog, and absolutely not on this computer (27 months old), and impossibly not with my current ISP (10 months on NBN with Internode). So, how the hell come, when I click on the blog link, it asks me if I want to comment as "FenceFurniture"????

Originally Posted by hurcorh

Birchwood Casey gun bluing is readily available on ebay and the likes. There are some videos on youtube showing how to apply it and the kind of result you'll get. Here's a video on benchcrafted's website from 6 years ago. Benchcrafted Blog

That website seems to imply that the Birchwood Casey Bluer is "The Method of cold bluing".
Cold bluing covers hundreds of formulas and dozens of methods. It's correct name is chemical cold bluing.
Cold chemical bluing looks nice but is the least physically robust of all the cold bluing methods which are in turn less robust that the hot bluing methods especially if objects are handled regularly.
Gun owners are constantly handling their weapons so there's a lot of wear but theres always a regular use of light machine oil involved in their overall rust protection system.
Unless this is done they will rust and even when they are not handles these light oils eventually evaporate away in time and they still still rust. Long term storage of these items usually requires the use of oil cloths for protection from rust.
Cold chemical bluing is a preferred method for guns because some guns cannot be hot blued and because cold chemical bluing can be readily used for touchup repairs.

The best cold chemical bluing agents usually contain chemicals that are too toxic to send by mail and those that are sending the toxic materials by mail may be liable for some heavy penalties.
There was an online independently conducted test of a dozen or so chemical bluing agents. I placed an order with the US supplier of the best chemical bluing agent and my order and credit card was accepted (including free shipping) but minutes later I received an order cancellation. Seems like I was the first out of US person to order it and they had not thought through the ramifications of shipping it.

The gold bluing standard is still hot bluing but this cannot be done to all objects and spot repairs are not very successful so if it fails it requires a complete re-bluing.

For things like handles that will not undergo a lot of handling a black matt epoxy enamel is still hard to beat as it will not evaporate. Even for handles that are handled often it would be easily better than any of the cold bluing methods.

Derek - you haven't mentioned what the handles are - that and the extent of handling would go some way to determining what to use.

Bob, first of all, thanks to you and all the other replies here. Everyone has possibilities, and then there are potential negatives, especially wear. I was on the point of pressing the button on Birchwood-Casey's Super Blue a few times, but your comments have made me pause each time.

I have ordered some cast iron stove polish, which gets wiped on and then heated. I purchased this early on. It has not reached me yet, so I cannot feedback whether it works as I want.

The handles are bright new cast iron. They look silverish at this stage, and I want at least a dark grey, or, better, a black.

The ones I have are the smallest (for the apothecary chest). Ironically, they could have been had in black, but the photos looked painted and the above pics looked darkish grey.

https://www.castinstyle.co.uk/produc...n-cabinet-knob

Regards from Perth

Derek

Thanks Derek.

Nice knobs BTW. The blurb says they come with a lacquered finish which will need to be removed to apply any other finish.

I'm not not sure about the cast iron stove polish method and its wear characteristics but I suspect it will be a pigmented wax and so will be equivalent to the carbonising hot oil method.
It reminds me of an old blacksmith method whereby the heated objects direct off the forge are dunked in a bucket of hot beeswax - it generally produces a nice little fire that has to be smothered, lots of smoke, and a strong hot beeswax candle aroma.

The stove wax should be more robust than any cold bluing method. You can always try it out for abrasive resistance by coating a small piece of cast ion and then carrying it around in a pocket and see how it wears - might also test out the pockets too.

Physical wear is only one aspect, the other more difficult ones are the acids and moisture from hands which is hard to test for. In terms of hand and acid moisture the epoxy flat paint will win that battle. Wear resistance can be dealt with by multiple applications of the spray. Another type of paint which would work is exhaust pipe black, its tough stuff but I have no experience with it in a handle situation

In terms of wear resistance your handles are ideal candidates for hot bluing but I don't recommend playing with hot caustic at 140ºC for a couple of hours, and disposal afterwards can be problematic. You would still need to try it out and after you spend money on the chemicals as it may still not produce the look you are after.

Bear in mind that any jet black finished look of any of these methods will change on handling as it will pick up dust and skin cells and lose its blackness. They can of course be cleaned but then the cleaner may change the surface character.
if you want it jet black you may have to coat with a mat lacquer but that too can wear off.
A grey might be better. The way to get nice greys is via cold fume, or hot bluing.

Here is a grey I did with cold fume bluing lakeside a bare steel handle. It's not my best effort as the surfaces were not well prepared or polished to what they should have been.
Some people that see this photo say its a brown-grey but that's mainly due to the colour toning of the surrounding wood, although that may also happen on your cabinet as well.
I'd offer to try one out for you but cold fuming is a Giant PITA (acids, time) and even then it may not reach desired wear and colour, all of which is why it is rarely done. These days I only do it for a bulk load of stuff that I know where I want to drive it to.

Bluing1.jpg

Presumably you don't want to spend weeks testing and they won't have a huge amount of handling, so if they start wearing/corroding after a few years there'll be no drama to retreat them with some other method?

I go with the wax and see what that is like.

Thanks once again Bob. It sound like the wax/polish may be the way to go.

Removing the lacquer is the first step. I came across this method on the 'Net ...

Make a mixture of Baking Soda and Water (1 Tablespoon of Soda to each Quart of Water) and bring to a boil.

While still boiling, immerse the item. One half at a time if your pot of solution is not large enough to immerse the item completely.

After about 15 minutes of boiling, the coating will peel and lift off. Remove from the solution and wash with hot water. (Remember to protect your hands from hot surfaces.)

Use acetone (or non-oily nail polish remover) on a cotton or wool pad to remove any remaining stubborn coating.

Any thoughts?

Regards from perth

Derek

Baking soda is sodium bicarbonate , a mild carbonate, that you can drink and eat.
Did you know that commercial soda water contains about a 1/4 teaspoon of this per litre. It makes it extra fizzy - try it (with some care) in your soda maker, unfortunately doesn't do much for your salt intake.

If you want to use something slightly more aggressive than sodium carbonate (foot baths salts) available at most supermarkets for about $5 for a half kg bag can be substituted.
A concentrated version is a moderately safe paint stripper for softer paints.
It's also safely disposed of down the plug hole.

The process sounds fine, any residual acetone will blend in with the wax..

Remember once you have done this the metal is now bare/raw cast iron (CI) and depending on the CI it may start to rust immediately so either have an air tight container with a pack of water absorbing crystals in it, or have the wax in hand to paint on.

If it develops a rusty patina, the best thing to do is not to remove it but convert it by boiling it for 10 minutes in distilled water - this will turn any rust black and you won't see it under the wax.

Thanks Bob.

Cheers

Derek