Thread: How to blacken steel

https://makeitfrommetal.com/how-to-b...eswax-at-home/

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I've tried this method (in the kitchen oven) and it does indeed work and looks real nice, but it did generate some smoke so if you have an outside BBQ oven suggest using that instead of an oven. Also you can general fit larger pieces in a BBQ oven.

As someone who runs dust/particle detectors inside a house 24/7 teven though it may not look that bad he huge volumes of sub micron particles generated by heating wax and linseed oil to 425F (220ºC) in a domestic oven is pretty scary. If you do this make sure you have really good ventilation, not just a standard stove top range which are pretty useless at ventilating the amount of fine (invisible) particles produced. The stuff will fill your house and takes hours to dissipate. Mind you the same applies to any general high heat oven cooking or using gas appliances that are not well ventilated.

It won't look black or perhaps as smooth but plain linseed oil will provide plenty of protection. Start by leaving the object in the sun on a hot (30ºC+) day for a couple of hours and then paint on the linseed, if it's too thick add a (little) bit of turps. Leave it to dry under a hot sun. It may take as long as a week to develop a fully hard surface. On rusted objects the rust can be passivated with something like tannic acid (Fertan) or other passivator. I like using tannic acid because it passivates to black.

Here's a before and after of a BS vice I scored from the men's shed.
Under the blue paint was deep layers of rust, mostly removed with a wire wheel on an angle grinder and the remainder passivated with tannic acid, then coated in linseed oil and left in the sun,
FinalBSvice.jpg

Here is a spoon I forged last Saturday and gave it some beeswax from our hive (I did not refine the wax in any way so it had a fair few impurities from the hive in it). Seems to give it a nice finish. I rubbed the beeswax on the hot steel - it was too hot to hold but tried to apply at the point where it had cooled enough not to smoke when you apply the wax. Buffed it off with a rag while still hot.

4C5AE917-2BF3-488D-8000-758FDEC56EBD.jpg

Originally Posted by Danger Mouse

Here is a spoon I forged last Saturday and gave it some beeswax from our hive (I did not refine the wax in any way so it had a fair few impurities from the hive in it). Seems to give it a nice finish. I rubbed the beeswax on the hot steel - it was too hot to hold but tried to apply at the point where it had cooled enough not to smoke when you apply the wax. Buffed it off with a rag while still hot.

That looks pretty good to me and was one of the ways the instructor at the blacksmiths course I attended blackened got us to blacken the tools we made. The other method was dunking into a light mineral oil but mine came out pretty scaly although it was probably too hot before dunking.

Does this blackening method that heats the steel to 425f effect the properties of the steel.
For example, if I had a motorcycle axle made out of 4140 and used this method would I likely reduce the strength.
Or if I took a grade 5 bolt and used this method, would I be asking for trouble.

Now for the disclaimer, if someone tells me it will cause no issues and I try it, I acknowledge I am trying at my own risk and will not hold them in any way responsible. I don't like this new world where it is always someone else's fault.

Steve

Originally Posted by Reidy41

Does this blackening method that heats the steel to 425f effect the properties of the steel.

That's about 220C, I suspect you'd need to get to at least 2-3 times that temp before there was any possibility of damage.

Originally Posted by elanjacobs

That's about 220C, I suspect you'd need to get to at least 2-3 times that temp before there was any possibility of damage.

That would depend on the type of material, most high tensile steels start to reduce in hardness, and therefore Tensile Strength, at temperatures above 200 degrees C with hardness reducing further as the temperature increases. There could also be the possibility of Hydrogen Embrittlement with High Tensile Steels.

Originally Posted by Reidy41

For example, if I had a motorcycle axle made out of 4140 and used this method would I likely reduce the strength.

For that application, why risk it? Here's what you need: https://www.claytonfirearms.com.au/p..._category_id=0

Huh...would have thought 200C was nothing for steel

It depends on the size of the object but most fully hardened heat treatable steels will lose between 2 and 5 points of RC hardness at around 220ºC
BUT
I also doubt 220ºC will do much tempering in 20 minutes, my experience it it takes about an hour for knife size pieces at these temps.

Besides I don't see these methods as intended for protection of hardened steel.

Perhaps more importantly is how accurate are domestic ovens at ever reaching an actual temperature and holding it. My testing shows they're not that good. The ones I've tested were all over the place.

[EDIT] I just found my tempering guide and the general rule of thumb is a one hour tempering soak per inch of thickness, BUT with a minimum of two hours is recommended for any size piece.
Liquid quenched steels may be tempered in one pass, but air quenched require multiple tempering cycles, and cooled to about 100ºC between cycles.

Originally Posted by jack620

For that application, why risk it? Here's what you need: https://www.claytonfirearms.com.au/p..._category_id=0

Well, the purpose of the question was to see if I am risking anything. I happen to have a very large block of bees wax and a bottle of linseed oil. If I asked a general question, such as does this effect steel, I would probably get a general answer.

I am becoming more educated now and can make a decision based on some logic as to if I would use this method.
The other reason for considering using a product like this is that I am finding some of the older simpler ways worked well. They just get lost in time.

Steve

Can of black paint works every time

Take it to the electroplate place

Originally Posted by azzrock

Take it to the electroplate place

Lol yep, it's hard to beat a commercial black oxide finish

Originally Posted by Techo1

That would depend on the type of material, most high tensile steels start to reduce in hardness, and therefore Tensile Strength, at temperatures above 200 degrees C with hardness reducing further as the temperature increases. There could also be the possibility of Hydrogen Embrittlement with High Tensile Steels.

I was unaware that Hydrogen embrittlement was a possibility when heating iron or steel, in fact I thought that heating steel parts which had been electroplated for example would drive off any Hydrogen which had been absorbed into the crystal lattice structure of the steel part. Have I been mistake in my belief?