Chemical Blackening of KTM models

[up148]

I've never asked about this and if I was told I've forgotten, but how did KTM chemically blackened the brass chassis, pilots and other various parts on their otherwise unpainted brass models. Does anyone know how this is accomplished?

AND, more importantly, how can you removed it without sanding it off. I'll be making changes and soldering on some of the blackened parts and having them in natural brass would be preferred.

[sarge]

I would guess the process is similar to gun-blue (which actually can be done in anything from a brown through blue to black).

I've never found anything for it but abrasive, though I never cleaned a mech and frame off completely and left it that way. I'd clean the location, solder whatever as needed, then touch up with that Hobby Black stuff we used to be able to get at the hobby shop if it wasn't going to get painted. I suspect black "cold-blue" from the gun store would serve the same purpose.

[healey36]

I've often wondered how the "blackening" process was done as well. A lot of the late-prewar Lionel stuff featured blackened metal trim and tin wheels, but it almost looks like the metal was somehow stained rather than coated. I have one 259E with darkened rims on the drivers, but it looks like they were painted. I'm not sure if that was original, but I think not.

[up148]

I'm pretty sure it's like a stain on the brass, by actually changing the chemical composition of the brass surface. Kind of like anodizing aluminum in different colors or gun bluing as Brian stated. I watched the gun bluing process on a program recently and the barrel, trigger mechanism and other parts were put in a heated chemical bath. These were custom made guns in the UK and costs upwards of $100K each.........rich guy toys.

[Norton]

I have used Birchwood Casey Super Blue to blacken brass. Its nowhere as effective as doing ferrous metals but it will darken it. It takes successive soakings and then rub off the scale. I am guessing KTM used some sort of hot process.
I just checked Caswell plating and they show nothing for brass but do have a blackener for copper. Might be worth a call.

https://caswellplating.com/

If you are not aware of them know they have inexpensive brush plating kits for tin and nickel among other products useful for plating siderods and other brightwork. They also have more expensive kits for electroplating for show quality restorations.

Pete

[up148]

Thanks Pete, that is great information to know. I was more interesting in removing the blackening for soldering, but I think Brian's idea will work fine. But, knowing a kit is made to change the color is something I will check out.

[E7]

Go on Amazon and search for Brass blackening solution....they have it!

Rich

[robert.]

Try soaking in Parson Sudsy ammonia.

[robert.]

Sometimes i use baking soda and lemon. Make a past. Pile it on and scrub wife a brush. You can let it sit before scrubbi g it. Yes BS. And lemon will fizz some. It will stop.

[up148]

I found information online that concurs with you suggestion Robert. If you're brave enough you can use muriatic acid as well, but I'll try the less dangerous methods first.

I also found a product that is made specifically to blacken brass. Might try that if I decide to paint this model. The plans at this time are to strip it and then leave it natural brass to see what was done to it.

[Rufus T. Firefly]

I also found a product that is made specifically to blacken brass.

I'd just go with the the product specifically to blacken brass.

I don't understand the baking soda & lemon thing; acid and base mixed together should just neutralize each. Muriatic acid is just hydrochloric acid. I don't understand how that might be good to use on brass unless you completely neutralize it later. We used to use vinegar (acetic acid) for cleaning brass and prior to painting, but again, you have to neutralize the acid. Leaving the acid (or base) on the brass is only going to cause problems later regardless of painting.

[bob turner]

Once in a while I would get ambitious, and strip a frame for painting. I would merely clean it up with fine sandpaper, block the pedestals with U shaped cardboard, shoot it with Scalecoat out of the Paasche, and bake for an hour.

I never once had any flaking or other problems. Looks better than a blackened frame.

[up148]

Well, I know removal results in a few weeks of months, but right now too busy on outdoor projects before winter sets in.

Even if I blackened it I would paint over the blackening,.......if I go that route. Too many other moving targets on this project right now.

[sarge]

Once in a while I would get ambitious, and strip a frame for painting. I would merely clean it up with fine sandpaper, block the pedestals with U shaped cardboard, shoot it with Scalecoat out of the Paasche, and bake for an hour.

I never once had any flaking or other problems. Looks better than a blackened frame.

I have never bothered stripping one to paint it; paint sticks to it just fine as long as you've cleaned any oils off like any metal surface.

We certainly agree the frame has to be painted when painting the rest of the loco; looks awful otherwise.

[bob turner]

Yeah - Most of the time I do not strip them; I just get them running and hope the area behind the driver spokes gets sort of blackened. Lazy.