Darkening cast iron?

[Derek Cohen]

Can anyone recommend an easy way to darken new silvery cast iron (handles). Ideally, I'd like them very dark grey to charcoal or black.


Regards from Perth


Derek

[Derek Cohen]

Can anyone recommend an easy way to darken new silvery cast iron (handles). Ideally, I'd like them very dark grey to charcoal or black.


Regards from Perth


Derek

[Mike King]

Stove polish. Or cold blue?

[lowell holmes]

I wonder if the cast iron would darken if heated with a torch?

[Lasse Hilbrandt]

its just a thought. what about that "bluing" liquid thats used on weapons ? it does not turn blue, but black. I don´t know how it will react with cast iron, but on soft steel it turns black almost instant

[steven c newman]

Disston was very good at heating things up a bit, then coating with mineral Oil....to get the backs of the backsaws blued....

When I rehabbed that spokeshave I accidentally had tossed into the fire pit....I had it down to bare metal....I used Gun Blue Paste...instead of black paint.
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Just wipe on, allow to dry, wipe off the excess...
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It will also bring out any logos...

[Jay Larson]

Not sure about cast iron, but I do that with steel. Heat it up and then put BLO on it while still hot. Turns it a nice dark gray.

[Adam Herman]

if you want to keep it raw and keep it from rusting, I would suggest seasoning them with unrefined linseed oil, and if they are food grade, unrefined flax seed oil. clean with something strong to remove all residue, use a rag and rub on a light coat of oil, put in cold oven and set for 500 for an hour after it gets to temperature. after the hour, let it cool and repeat. I do 4 or 5 cycles on raw cast and when re seasoning my pans I do a couple coats after a vigorous scrubbing with chain-mail scrubbie and salt. it should turn out a beautiful matte black.

flax and linseed are the same thing. one is generally processed on food grade equipment and the other is not. very low smoke point so the oil will polymerize. refined oil has a much higher smoke point.

[Joe Bailey]

Interestingly, this is one of the undesirable side-effects of soaking in citric acid -- a technique many use for rust removal.
It imparts a dull-to-dark grey tone, depending on the soak time.
My understanding is that Evaporust* has the same side-effect.

Another option, if you can find it, is "Stove Polish" or "Stove Blacking"


*don't know if you have this at your location

[Bill Orbine]

Leave a leaky cup of coffee on it!

[Robert Hazelwood]

IF the part is fairly small then rust blueing works well and should be more durable than cold blue. You clean and degrease the part, apply the rust blueing solution, wait a few hours for it to rust, then boil it in water for 10 minutes or so to convert red rust to black. Then you wire brush it to remove anything loose, and repeat the process if you want it darker. 3 rounds usually is enough for what I do. I've done a lot of chisels and plane irons, but also a cast iron lever cap, which darkened nicely.

Another method that blacksmiths use is to heat the part in a forge or with a torch and apply oil. Basically like seasoning a cast iron skillet. Might not be the best feel for a handle though, could be a little sticky.

[J. Greg Jones]

Seasoning a cast iron skillet is what I would recommend, Google 'jeffrey rodgers culinary fanatic' to find the guy that does it best. Properly seasoned cast iron will resist rusting and will not be sticky.

[John Schtrumpf]

If you want to experiment, I have used this process twice. It is more or less based on a rust conversion and cast iron cookware preparation.

Oh, and a link to Jeff Rogers seasoning (a little different then what I do)
http://theculinaryfanatic.com/cast-iron-restoration-maintenance/jeff-rogers-cast-iron-seasoning-method/

Step 1: Clean

-Wash with soap and water to remove any residual oil and other contaminants.
-Rinse well with water.
-Dry in a 200ºF oven for 5 to 15 minutes.

Step 2: Etch

-Soak in distilled white vinegar for 1 to 4 hours.
-Rinse well with water.
-Dry in a 200ºF oven for 5 to 15 minutes.

Step 3: Patina (rust conversion)

-Heat some Tannin Tea* to boiling (microwave) and brush it on.
-Dry in a 200ºF oven for 5 to 15 minutes.
-Rinse well with water.
-Dry in a 200ºF oven for 5 to 15 minutes.

-Repeat around 3 times (when the patina looks good).

*Tannin Tea recipe:

Brew a strong cup of tea using 5 to 6 (real) tea bags.
Optionally add a teaspoon of instant coffee, if you have it.
Optionally add a teaspoon of wine tannin, if you have it.

Step 4: Season (coat)

-Wipe on vegetable oil (flaxseed and linseed oil works if you have it).
-Wipe off the oil with a dry cloth (this leaves a thin coating).
-Position your piece(s) in the oven so that if they drip, the blob formed on the piece will be in an unobtrusive area.
-Put aluminum foil on the bottom of the oven to catch any drips.
-Bake in 350ºF to 400ºF for 1 hour.
-Turn off the oven and let cool for 1+ hour.
-If the seasoning is sticky, bake again at 400ºF.

-Repeat 1 to 3 times (when it looks good).

Note: If you have a self-cleaning oven, you can use it to ash (remove) the seasoning.

[steven c newman]

"Wipe on, wipe off."
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What I use to bring out an etch.

[Vincent Tai]

https://mypeculiarnature.blogspot.com/2014/08/quick-rust-bluing-back-in-black.html
I came across this method a while back and have found it to create a durable black finish like that of of Japanese tool with its Kuro skin; forge finish. The blog is worth a read too, a favourite of mine.

This is similar to John's method.

I have experimented with it a lot a while ago and came up with some variations on the rust solution which fail my memory. I will try looking for any notes I've written. They were particularly quick acting, I dropped a kanna blade in and 30 seconds later there was bubbling rust and the solution was a rich rust colour in 2 minutes.

Here is an axe which I did this process on for a couple days. I found that a boiling pot of water was better than a steamer and the only option for something this sized. I let it boil for hours at a time.

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​here it is in its original sorry shape.

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A little less sorry looking now.

The axe only had some oil and rust removed before I started rusting it, I didn't care about sanding every pit and crevasse away. Or any sort of sanding. A bbq brush and some soap was basically the prep. Turned out okay.

This is harder to do on polished stuff, a natural rust is more suitable. like the ones that would form on a nice veritas or LN plane in a humid environment. Even and thin.

389422
bottom right is a kanna blade that I started the process on and at first it had a wonderful silky gray finish as shown but as I experimented with etching with a citric acid bath and then a way too strong rusting solution I made, it became very pitted and I had to regrind the ura.

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It took about 100 seconds for that to happen. Perhaps it's for the best If I don't find my recipe.

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A little heat and It really chewed through the metal. I think a natural rust from a humid environment with a light pickling from citric acid to start off with would be a good way for a polished cast iron handle.

I suppose this isn't an easy or fast method. Might not be suitable to your taste at all. I have seen your Kiyohisa (or are they Kiyotada) paring chisels and the Kuro finish on those haunt me, I think images of near perfect Kuro finished tools spark me to do really awful experiments on anything steel or iron.

http://benchcrafted.blogspot.com/2011/09/omega-3-fatty-acid-for-your-cast-iron.html

I just remembered about this blog post; this may not give the quite the colours you are looking for but isn't very hard to do and noticeable darkens things up.

have fun experimenting,

Vince

[Brian Holcombe]

I use something similar to what Steve uses; brass black. For some reason it works well on iron.

https://brianholcombewoodworker.com/wp-content/uploads/2018/06/img_0872-e1530068626162.jpg

[dennis davidson]

Second the linseed/flaxseed oil. Turns grey cast iron nice and black after heating in the oven.

[John E. Braun]

These guys make something that should help : https://jaxchemical.com/shop/jax-iron-steel-nickel-blackener/ I have not used the product for cast iron, but have used their bronze darkener to good effect for years.

John

[Kevin Perez]

Be careful using cold blue (gun blue). It can leave a smell on the metal that doesn’t go away. I used it on an old Opinel knife just for kicks, and while it looks great, it has a smell that gets on my hands when I touch it. The smell lasts for months and months (on the metal, not my hands...).

[Derek Cohen]

if you want to keep it raw and keep it from rusting, I would suggest seasoning them with unrefined linseed oil, and if they are food grade, unrefined flax seed oil. clean with something strong to remove all residue, use a rag and rub on a light coat of oil, put in cold oven and set for 500 for an hour after it gets to temperature. after the hour, let it cool and repeat. I do 4 or 5 cycles on raw cast and when re seasoning my pans I do a couple coats after a vigorous scrubbing with chain-mail scrubbie and salt. it should turn out a beautiful matte black.

flax and linseed are the same thing. one is generally processed on food grade equipment and the other is not. very low smoke point so the oil will polymerize. refined oil has a much higher smoke point.

Thanks Adam. I will look into this.

Regards from Perth

Derek

[Derek Cohen]

"Wipe on, wipe off."
389428
What I use to bring out an etch.

Steven , this brand is the only bluing chemical available in Australia. Does it turn the iron black or black with a blue sheen?

Regards from Perth

Derek

[steven c newman]

Black. Haven't noticed any blue tint.

[Derek Cohen]

Thanks Steven.

Regards from Perth

Derek

[Jeff Ranck]

Wow! Who knew that these were so many ways to darken cast iron.

[lowell holmes]

Propane torch might darken the Cast Iron.

[Derek Cohen]

Here's where I am at this stage:

I have cast iron knobs for the chest I am building. The are silver-light grey in colour. I would like them to be charcoal-to-black.

The issue with cold bluing formulations is that they create a finish that wears with handling. Drawer knobs get handled frequently (although these should not get daily use).

Hot formulations are more durable than cold formulations. I have a good friend who is clued up on the chemistry of these products. I mentioned that I had ordered a stove polish. This is rubbed on and then the iron/stove is heated. Lots of smoke issue, and then the finish gets rubbed back. He said that this is equivalent to the hot formulation, and should be durable.

This is the product I have ordered ...

https://www.rubbedin.com.au/Product/26/Fuel-Stove-Range/Cast-Iron-Stove-Polish#horizontalTab1

I ordered one extra knob, and will experiment on that when the polish arrives.

Regards from Perth

Derek

[Derek Cohen]

Here's where I am at this stage:

I have cast iron knobs for the chest I am building. The are silver-light grey in colour. I would like them to be charcoal-to-black.

The issue with cold bluing formulations is that they create a finish that wears with handling. Drawer knobs get handled frequently (although these should not get daily use).

Hot formulations are more durable than cold formulations. I have a good friend who is clued up on the chemistry of these products. I mentioned that I had ordered a stove polish. This is rubbed on and then the iron/stove is heated. Lots of smoke issue, and then the finish gets rubbed back. He said that this is equivalent to the hot formulation, and should be durable.

This is the product I have ordered ...

https://www.rubbedin.com.au/Product/26/Fuel-Stove-Range/Cast-Iron-Stove-Polish#horizontalTab1

I ordered one extra knob, and will experiment on that when the polish arrives.

Regards from Perth

Derek

[lowell holmes]

Not sure about cast iron, but I do that with steel. Heat it up and then put BLO on it while still hot. Turns it a nice dark gray.

Did you ever look at the bottom of a cast iron skillet. They are certainly black.

[Bill Orbine]

I'll put aside my joking around and suggest that you Google "Black Magic Patina". You are looking for Sculpt Nouveau. This is a product I had forgotten till I saw my friend's blacken tin mantle shelf.

[matteo furbacchione]

I wonder if the cast iron would darken if heated with a torch?

Yup, but you need to add an oil based product (I.e.e wax) to the hot iron, and then it goes black. The wax/oil needs to be cooked into the iron so the metal needs to be fairly hot. Well past the point where wax boils but not red hot.