Chemical Black or Paint?

[greasemonkey]

Hi All
I am rapidly approaching the moment when I need to start painting the Dougal I am building but I am undecided as to whether or not paint the finer parts such as the brake gear or to chemically blacken them. Does any one have any experience of chemically blackening steel and its application in this environment?

thanks

Andy

[John Lee]

greasemonkey said:

Hi All
I am rapidly approaching the moment when I need to start painting the Dougal I am building but I am undecided as to whether or not paint the finer parts such as the brake gear or to chemically blacken them. Does any one have any experience of chemically blackening steel and its application in this environment?

thanks

Andy

I've tried the chemical blacking Andy, for the same reasons as you, to preserve detail.

It does not seem to do anything to prevent rust, damp still penetrates and rust breaks through.

A preventative is, of course, a bit of oil knocking about, as you would do with your unpainted motion, but you would not want oil near your brake gear I suppose, or at least on the brake blocks.

Regards,

John

[chris vine]

Hi Andy,

I found that the simple dipping type of chemical blacking is not very corrosion proof but clearly a bit of oil, (or the makers recommend a silicone spray) helps a lot.

I does depend on what type of blacking you use. Some of them are a nickel plating process which ends up black. Thses will be very corrosion resistant.

I found that a good paint, such as Trimite's semigloss black is good for chassis parts and brake bits. I does not go on too thickly if you are careful with it. For example if you spray machined cast iron parts you can usually see the machining marks through the paint.

Chris.

[SteveW]

Andy,

I've used the Plaskote, high temperature spray black with some success although I'm still painting so haven't got it hot yet.

I've also used smooth hammerite and found it to be TOTALLY crap for this sort of stuff. It creeps away from all edges and although non-tacky fairly quickly stays soft for days/weeks. The saddle tank sprayed months ago still fill the bedroom with a solvent smell but does look quite good. I was looking here for a hard paint that didn't circum to hot sparks like the previous finish of Halfords car finest.

The plaskote by contrast is a joy to use. It seem to go on to bare metal, re-coats with ease, goes on thinly sticks to the edges and should survive the heat.

However, I bow CV (above) for a definitive statement even if its a bit late in my own case.

[stantheman]

Hi all chemical black fans.

When working, the company found that 'proper' chemical blacking not only cost them good money, they also used to only get half the bits back from the blackers, due we thought to general mis-handling. So, one way around this was to give somebody the job of heating (carefully) with a flame the small parts to cherry red, then dunking them into a pot that contained, would you beleive, whale oil. Leaving them in until cold then wiping the excess off. They were black and they did survive for some time before losing that newly blacked look.
I should say that these parts were only made from general mild steel so there was no fear of them becoming hardened.

Not sure where you could get whale oil from these days though, just a thought.

Stantheman.

[gilesengineer]

Strangely, I have managed to use the Smoothrite spray very successfully, (although the first couple of coats do tend to creep away from edges slightly - I suspect this becomes more of a problem the smaller scale you go....). I use it (the black) for smoke boxes on a couple of loco's, and it tkes the heat perfectly with a good and very robust finish. I use the coloured sprays for tanks and platework with equal success - except the one ocasion I sprayed an un-lagged boiler (on a Maxi-track) in light blue, and it changed colour with the heat. (I then sprayed the boiler black....). On all other occasions I've found it highly satifactory, although it is frustrating not being able to over-paint for 6 weeks....
I've not enjoyed trying to use the brush-on stuff though....

[ron]

Hi
Stantheman's system for blacking metal works well with used engine oil as well [non synthetic] if you can't find a convenient whale, it makes a good decorative finish but is not very robust or corrosion resistant.
Frost restorations offer various metal finishing and blackening systems, might be worth browsing their catalogue or contacting them.
Ron

[greasemonkey]

Hi All
Thanks for the replys. Johns coments reflect what I heard about the chemicla finishing needing a sealant to preserve it and why some companys sell one, but I wonder how durable it will be on a live steam model!! Whale oil might be a problem, but your idea Ron rang bells. I made a set of firing irons about 15 years ago and treated them by heating to red and quenching in engine oil. The finish is pretty durable as I'm still using them now and there's no rust on them despite being used in many a down poor. Thanks for the reminder think I will try some experiments down that line, now all I need to do is find some mineral based engine oil!
thanks
Andy

Andy

[ron]

Andy, if you want to come and change the engine oil in my TR6 you can have plenty ;D and it's usually pretty black!

[Lurkio]

Hi all,

Following up on stantheman's post, I had need to provide a blackened finish to mild steel bits on a project in a factory. Heating and quenching (in whale oil as well which was I believe widely used then for heat treatment) provided a finish from pale straw through to black.
Subsequent reheating and quenching achieved better, blacker finishes!
It was fine for rust prevention in a factory environment, but I wouldn't expect it to have lasted for too long in a wet environment.
I remember a similar process when an apprentice, but I recall we used some form of dissolved 'salts', gradually heating the liquid containing the parts until the colour required was obtained (pale sraw through to deep blue). Some really nice finishes could be obtained. Once again, more decorative than rust inhibiting, but I wonder if anyone here knows more about these 'salts'?

Lurkio.

[steamjohn248]

Having admitted that we dont reckon to go in for Model Engineering, we simply build small working steam locomotives, on the last loco,we sprayed slightly thinned smooth Hammerite straight onto bare steel, de greased with Hammerite Thinners. I would'nt put one of our engines in an exhibition but it seems to stand up to its work ok It even seems to stay on the stainless steel tanks as long as you dont hit it with anything sharp and heavy.

[steamjohn248]

Oops, Suppose I'll be in for B********g for putting such big pictures on. Not only do we not do Model Engineering we're not very computor literate .

Ah Well

Steamjohn

[greasemonkey]

Hi Ron
Thanks for the offer but your a little far away from me in down here in windy hampshire! I will ask a local guy who,s got a Triumph Vitesse! At least it will still have a good pedigree.

Andy

[Noddy]

Oxide blueing is a pretty poor rust protection (its' protection is only as good as the oil or wax you coat it with), and depending on the grade of steel, doesn't always give a very good black either.

Traditionally it was achieved by inducing the part to rust, there are all sorts of witches brews containing chemicals that are likely to get you a visit from the anti terrorist cops or at least poison your cat or speed your divorce...

These were thinly applied to the de gresed metal to encourage formation of a fine rust. the part was then boiled in clean (de ionised or distilled if you have limescale probs) water, the loose brushed off with a wire brush or de greased wire wool and the process repeated until the desired colour was achieved. The ref is RH Angier, firearms bluing and browning.

There are also hot processes using a concentrated solution of sodium Hydroxide and Sodium Nitrate (again, you'll probably get a visit from the boys in blue if you try to buy the nitrate). I have heard suggestions of mixing sodium hydroxide and ammonium nitrate fertiliser to get the sodium nitrate, but the ammonia is displaced and will stink the building (parish) out.

Anyway, the shade of black or blue is sensitive to composition and concentration of solution, it boils at well over 100c and will burn if you get splashed, and the result is not a good rust protection.

The cold bluing kits seem to come in several types, those that precipetate selenium or copper (the copper ones then use ammonium or sodium sulphide to give a black finish) will encourage rusting in damp conditions.

The oxide cold bluing ones are simillar to the rust and hot bluing, not giving good protection.

Oil blacking (sump oil, vegetable oil etc) does seem to be durable (tried cleaning an oven lately?) and easily achievable (it was used on the actions of No4 lee Enfields).

Phosphating is another possibility, Angier contains the recipe from the original parkerizing patent. Phosphoric acid is the basis of most de rusting potions and is also used by dairy farmers to remove milk scale from their equipment. Various gun books repeat the old Parker formula of phosphoric acid and manganese carbonate ad nauseum.

Phosphate finishes, (iron, manganese and zinc in order of increasing thickness) are mechanically v strong (they are used before deep drawing of steel to retain lubricant) and coupled with heating the part to around 100c and dropping it into waxoyl, give pretty good rust protection.

I think there were some pretty good discussions of blacking archived under guns and under metalworking in Norman Yarvin's Yarchive (try a quick google). The Gunsmithing kinks books (camden sell them) give tips for brownells proprietry potions and some improvised ones.
good luck

[Noddy]

Just for completeness, the Horologists go in for temper bluing, with various cunning plans like heating small pieces in sand or under a glass to get even heating and even colour. as a protection against rust, it is probably worse than the rusting, boiling and brushing method, but it does look nice. the Horologists use a clear lacquer to prevent rust. I used to have an old BSA Martini Target rifle (£5 out of the scrap bin and £15 to get it threaded for a silencer) and the action on that had been temper ("charcoal") blued, but years of neglect had allowed the orange moths to attack it, so it looked a bit scabby when I got it.