Sand Blasted Radiator – Can I Reproduce the Original (unpainted) Chocolate-brown Patina?

KevinK

All of my 13 radiators have been painted. All are, to varying degrees, experiencing paint chipping. (Brand: American radiator; installed: 1927.)

In their original as-installed state, the radiators were unpainted. Instead of paint, they had a beautiful dark chocolate-brown patina. The surface had a medium/fine sandpaper-like texture. I really like the original color and texture.

I recently had one sandblasted. What an improvement! What I am left with, after the sandblasting, is:
1. Color: gun-metal gray;
2. Texture: the original sandpaper-like texture.

My original post-sandblasting plan had been to spray paint the radiator (primer coat, followed by gloss white coat). However, as the radiator sat for several weeks, I noticed that it spontaneously started oxidizing to a rusty-brown (i.e., red-brown) color. On a test area, I accelerated the process by wiping it with a damp sponge. Result: enhanced oxidation; same red-brown color.

So, now I am left with the texture that I want, but, color-wise, I get a red-brown color, versus the chocolate-brown that I want. Also, I am concerned that the oxidized iron (i.e., rust) will rub off.

My questions are:
1. Does anyone know how the original chocolate-brown patina was achieved?
2. And, more importantly: does anyone know if/how I can reproduce this same patina “at home”? (Instead of spray painting.)
3. If I leave the radiator to oxidize naturally (or accelerate the process with moist sponge) will the resulting rusty patina rub off (e.g., on clothing)?

A thought: I wonder whether, as part of the manufacturing process, a wash (or some type of coating) was applied. Such wash/coating would presumably achieve two purposes: i. produce the chocolate-brown color; and, ii. seal the surface, and thereby prevent oxidation and “rust rub-off.”

Thanks.

Fred

You can accelerate the patina by washing it with a water/vinegar solution. It will rub off because it is just rust/oxidation of the cast iron. If you can find a high temp clear coat or polyurethane, once you get it close to the color you want, seal it. I suspect that reddish brown will become a chocolate color when the clear coat is put on it. Try a little test with a piece of cast iron.

Mark N

Are you sure the rads weren't originally bronze and they aged to that color? When I removed my rads to have them sand blasted and powdered coated, the backs of some of them still had the original bronze finish and it was a dark brown color.

KevinK

Response to Mark N: Yeah, I'm sure. My neighbor's radiators (same vintage) were never painted. They look exactly the same as the exposed surfaces of mine.

SWEI

You might experiment with some gilders paste.

hot_rod

here is some paint info for radiators and pipes

http://www.oldhouseweb.com/how-to-advice/no-acrylic-latex-paint-for-radiator-pipes.shtml

Maybe the clear coats would also be acceptable from SW?

LarryK

There are chemicals you can treat the iron with to give it a dark brown patina. Try the Birchwood Casey company. I think they sell small quantities to gunsmiths. They also have some topcoats that might be more suitable than lacquer. Call them and speak to an application engineer to discuss your situation.

KevinK

LarryK said:

There are chemicals ...

To LarryK: Thanks Larry. I will follow up on your suggestion. I also plan to do a web search when I have a chance.

JerseyJon

There's a British company that makes and restores beautiful natural metal radiators. They use linseed oil, which is a drying oil that will create a protective layer to halt oxidation. I just took a radiator down to metal and plan to oil it. I can post pictures when I get it done. When you buy a cast iron pan chances are that nice black sheen is from a flax oil seasoning. So-called boiled linseed oil is basically flax oil with chemical additives to make it dry faster.

KevinK

JerseyJon said:

There's a British company ... They use linseed oil, ... I just took a radiator down to metal and plan to oil it. I can post pictures when I get it done.
...

To JerseyJon: If you have a site with "how-to" info, and you have the time, please post.

I did a quick check on the Birchwood Casey co. that LarryK reco'd. Unfortunately, the treatment that that co. provides requires heating the metal to 275 deg F! If I find out anything more, I will post.

LarryK

They have a bunch of cold patinas, too. The company I work for uses them daily. I just looked and I see the industrial finishing side of the company is called Birchwood Technologies. Try this for one product https://www.birchwoodtechnologies.com/Presto-Black/index.html. Then look around they also have brown, I think. The linseed oil might be a good way to seal it, if you like the smell. I probably would.

We take the chemical full strength and rub it in with Scotchbrite pads applying more chemical as you need it to make it even, then rinse with lots of cold water. A baking soda solution rinse is good insurance against future rusting, then more cold water. Dry it with rags then seal it. That's what I would try to start.

The oil by itself might darken over time, but you could accelerate the process by adding a tint. In fact that sounds like the easiest way to get what you want.

KevinK

Thanks for the add'l info, Larry. I'll pursue your link. This is a back-burner project, so it may take me some time, but I will post as I find useful info.

JerseyJon

Keven, this is similar to the site I was thinking of. They polish the metal until it looks almost burnished. projectbook.co.uk/article_122.html
(I haven't taken mine down this far. Mine have a little more texture and patina.) The finish is just a thin coat of oil or probably two or three thin coats. They say WD40 or linseed.
My plan, based in part on this blog (fullchisel.com/blog/?p=1157) is to use linseed oil cut 1:1 with low odor mineral oil. Wipe on a thin coat. Let it air for 10 mins. Wipe off any excess and let it oxidize for 24 hours. I'll give it a light rub with fine steel wool and repeat for at least two or three coats. I'll buff the final coat.

LarryK

I work for a company that makes metalwork for high-end interior architecture. I've never actually re-finished a radiator up to now because most rich people like to cover up their radiators. I never thought about any of this until I bought a house with a one pipe system a few months ago, but I do have some professional working knowledge of metal finishing.

When a foundry sand casts something like an iron radiator they can take more or less care with the surface texture by dusting the pattern with layers of very fine sand before they ram up the mold or else not and just ram it up with sand from the molding floor. Look at this site: http://www.peguerin.com/ . Almost everything they do is sand cast and you will see how detailed it can be. So if you have a fancy old radiator that was cast with a high degree of detail and a smooth surface and then polished please don't sandblast it!

Most radiators you see will have a more or less rough texture from the coarse sand used. I think you can blast away on these! The surface can come out pretty rough so a final blast with glass bead can knock down the sharp peaks. There is a variety of media that can be used so discuss the options with your sandblaster.

One side of the radiator probably faces the wall so you can use that side to try different finishes before committing to the whole thing. You could try hand sanding. Work your way from a course grit to finer. A freecoat type paper should work well. But I think it could be a lot of work. Nickel plating would look very nice on an old radiator, I think. If you're made of money, bring your radiator to us, but don't worry if you're not. I can't afford to hire myself to do this stuff. www.kernrock.com.

SWEI

Walnut hull blasting, anyone?

Pure tung oil polymerizes more easily than linseed. Mix in a bit of pure carnuba wax and you get a really nice finish.

KevinK

LarryK said:

I work for a company that makes metalwork for high-end interior architecture. I've never actually re-finished ...

To LarryK: Update: Thanks for your input. I've had to focus on other matters for a while. As soon as I have had a chance to follow up on your, and the other, suggestions, I will post a follow-up.
~KevinK

KevinK

JerseyJon said:

Keven, this is similar to the site I was thinking of. They polish ...

To JerseyJon: Update: Thanks for your input. I've had to focus on other matters for a while. As soon as I have had a chance to follow up on your, and the other, suggestions, I will post a follow-up.
~KevinK