Would Like to Learn about the coatings etc

[MrWhoopee]

We recognize a mad mixture of all these oxides, including magnetite as mill scale. A fresh mill scale is hard, and protective, and if sealed, can be attractive, but if left to itself, it will rust through and fall off. The stuff is quite useful, until you want to weld on it or machine it.

The hearth under my wood burning stove is 1/4 HR plate with a beautiful hard black mill scale. It has never been treated in any way.

 

[graham-xrf]

The hearth under my wood burning stove is 1/4 HR plate with a beautiful hard black mill scale. It has never been treated in any way.

Hmm - clearly the oxide is protective. I also have a woodburner. They get hot, but are generally indoors. Maybe its the dryness, along with the heat conditioning that keeps them looking OK for decades.

I know that rolled steel, bar and plates as used in oil rig construction, and shipbuilding works, were traditionally left outside to "weather", basically until the mill scale started to fall off. I think heating a steel item a certain amount, though not so hot as to have it become a hardening process when oil quenched, can leave it with a blue or dark colour coating which can be buffed up and oil sealed

Pretty much most parts we make will look nice and shiny at first, but a few weeks or months later, they will be all brown and less functional, especially if some bits are close fitting. I think most need a finish of either painting, plating, bluing or other oxide sealing, or they need to be kept cleaned and oiled, maybe like one might treat a good hunting rifle.

 

[Mill Lee farm]

I have experimented with 'browning' the cast iron rim-lock door latch hardware on my bathroom door of my 1768 farmhouse. I cleaned and degreased real well and wire brushed most of the rust off trying to leave light surface rust. Some areas were sanded because the rust was thicker and unsightly.

I brushed them with the salt/hydrogen peroxide mixture mentioned earlier to promote flash rusting. You want to try to get a light even rust coating on the entire part. probably best to leave the part for an hour or more but I was impatient.

Dropped it in a boiling pot for some amount of time (10-15 min I think? I don't remember exactly) which chemically converts the rust to a grey black.

Pull it out and dry it, then recoat with peroxide solution and repeat. The idea is that you catch any of the surface missed in the earlier steps and build up the converted surface.

I think I repeated the process like 5-6 times?

After the final boiling, dry the part very well and drop it in old used motor oil to soak overnight. This drives the water out and allows the oil to penetrate and soak into the new coating. The result was basically gun black and very nice looking!

The oil wiped off very well, did not leave an *oily* feel to the part. Maybe slightly, but a lot less than you would think. It also didn't have a strong smell (I was afraid it would smell like used motor oil).

The finished latch has been on the inside of the bathroom door (damp shower etc) for two years now and still looks good. No rusting so far. It will everntually need some light re-oiling but so far I love the look and rust resistance!
Beside the asthetics, the mechanism continues to work smoothly which was what started the project. Paint is great but has no lubricating properties (actually sticky!) and the wear areas remove the paint leaving rust behind and rough action.... Then your shooting oil in it which DOES smell and leave an oily touch.... But this is a machining forum, not an old house forum lol.

Now.... This probably wouldn't be my choice for precision parts as it would amost have to change your finished dimensions, but a great idea for other things like clamping blocks etc. Also pretty darn cheap! You don't need the peroxide really. That's just to speed up the process. I believe gunsmiths set up steam boxes and leave the gunbarrels etc in the boxes to get a natural fine/light rust that is as even as possible.

Lots of youtube videos out there.

I would like to experiment with chemical bluing as well.

 

[Mill Lee farm]

Just some photos:

Before




After browning all the parts including mounting screws & springs



I regret not taking the remaining paint off the faceplate. You can definitely see the painted & non-painted areas

 

[Mill Lee farm]

Oh…. And here is a video I just uploaded showing the mechanism working.

I can’t be the only one fascinated by how they produced old cast iron rim-locks. Nothing was machined or sanded after production short of the actual latch bevel and deadbolt portions that protruded from the interior. They even had all the sprue leftovers where they were cut off the main casting sprue. Didn’t try to clean them up.
Great engineering to cast the whole thing and have it function rough cast!

now I’ll stop hijacking the thread. Apologies!