Blacking hot steel in oil

This crude method seems to give a convincing finish - a lot better than unfinished steel, at any rate. I was wondering if members have tried this cheap and cheerful method and how it stands up against rusting.

My results would be no good for a gun barrel but It's only for a tool, to be used indoors and mainly in the kitchen.

Sounds like case hardening to me

You dont heat it up hot enough to harden it. Just until it turns black. It works ok. You can get some rust over time. Helps if you spray it with WD40 after blackening. And it will wear off over time if constantly handled. Used engine oil works well.

You may think it ‘crude’ but if it works, it is simple, rather than crude.

Several threads previously, if you search for blacking or blackening - and possibly other key words.

I worked many years ago for a company making scientific instruments,the BA steel screws were polished and then sent for nickel plating, if for any reason the supply of screws for a batch of work run out ,there was quite a long lead time to get nickel plating done ,so the use of oil blacked screws was acceptable ,the usual practice was to polish and oil black the screws ,usually about a 10 to 20 items .the method was to place the screws in a tin lid about 2 inch dia,squirt a small amount of oil to just about cover the screws ,place tin lid on a stand over a Bunsen burner,heat them up until the oil caught fire and let the oil burn itself out. screws sizes were usually ,4 ,6,and 8 BA and blended in quite well with the black microscope bodies .

I typically find 3 to 5 years rust protection outside, maybe better in sheltered areas, and essentially indefinitely in the workshop. But it does wear off with handling.

Way I do it the surface does stay very slightly oily for a fair while. Not overtly so, more '"didn't think that was oily!" when you put it down and find the tiniest trace on your hands. Which may not be good in the kitchen.

Maybe spraying with WD40, as Hopper does, and carefully wiping off will leave a clean surface. Or perhaps try IsoPropanol alcohol.

That said I'm seriously slap dash about the whole process. Heat the bit up to blue(ish) and dunk it in the pint (ish) of oil I've had under the bench for so long I've forgotten what it is. Probably Castrol Magna BD 50 or Hyspin AWS 32 but it might be Shell Rotella. Maybe 15 years and counting methinks!

Gave up on old engine oil a long time ago as the results were too variable in colour and durability. Which I put down to all the additives and buts that make it multigrade. I recall getting all bad tempered when 5 parts came out about 8 different colours and grabbing the nearest bottle of straight oil for a do-over. 45 years or so back when I first started this old engine oil worked OK.

Clive

Used engine oil is nasty stuff and best avoided. I tend to use supermarket rapeseed oil which works very well.

Doug

I think that's a good point. The item I have made is an octagonal steel plate with a handle to let me heat up my aluminium espresso coffee maker on an induction hob. It works pretty well and the handle will allow it to be lifted off without scratching / breaking the hob.

I think the way we are told to 'season' a new steel wok is much the same thing. You get it hot and slosh cooking oil round it until it smokes. You get various colours and the wok looks 'used'. It makes a pretty good non-stick surface but you have to leave a film of oil on it ig you want to avoid a film of rust after week on the shelf. The figure of "years" , above, is encouraging tho'.

This plate will need to be heated for a while before I can avoid complaints about the hot oil smell (super sensitive noses on the distaff side). I don't want it to affect the glorious smell of the coffee either. Perhaps another cycle using rapeseed oil is called for.

Great to read all the personal input on the thread. Just what I needed. Cheers.