Author Topic: Phosphoric Acid - Rust Removing Technique  (Read 261 times)

Offline kleenax

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Phosphoric Acid - Rust Removing Technique
« on: March 17, 2018, 10:57:36 AM »
Just finished this part, so I thought I would share since we were talking of Oxalic Acid use last week.

This payphone daisy wheel had some rust on it, but still in pretty good shape, so I wanted to remove JUST the rust before I touched up the chipped white porcelain with a Sharpie Oil-based Paint Pen (see photo). Notice how much brighter the colors are on the daisy wheel too; the phosphoric treatment really makes the colors POP!

I use Phosphoric acid (bought @ Home Depot) "Prep n' Etch" in the paint section. I always use it straight out of the container; no dilution (don't know the % of acid it is tho). It's not a SUPER-strong acid solution, but rubber gloves, an apron, and safety glasses are recommended.

I have several inert plastic and/or glass containers that I use for immersion of my parts. You will have to experiment with the length of time that you soak your parts; just don't leave them in there for days-and-days; they will eventually dissolve! I have found this to be safe for use on Nickel and Chrome plated parts that have corrosion too; works GREAT!

This particular part soaked for about 4 hrs. while I was working on another phone. I periodically inspect the part to check on the progress of the removal of the rust stains. Sometimes, after only about an hour of soaking, you can then remove the part and brush the rusty area with a Q-tip and the rust will come right off! Other times (deeper rust), you will have to leave it in the solution longer.

After you are satisfied with the removal of corrosion, remove the part and gently brush it with a SOFT brush or q-tip to get down to the parent surface, and then rinse well in clear water. After rinsing and drying, I usually use some type of polish on plated parts to help prevent future corrosion and bring out the luster of the original finish.
« Last Edit: March 17, 2018, 11:06:00 AM by kleenax »
Ray Kotke
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Offline cihensley@aol.com

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Re: Phosphoric Acid - Rust Removing Technique
« Reply #1 on: March 17, 2018, 11:40:16 AM »
Thank you for the tip. Looks great.

Chuck

Offline AL_as_needed

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Re: Phosphoric Acid - Rust Removing Technique
« Reply #2 on: March 17, 2018, 04:15:14 PM »
I have had similar luck with acid (and base) rust removal on a variety of things from lanterns to tools. So long as the base metal is good quality and you treat it before it rusts over again, its a great way to speed things along. How do those paint pens hold up? Do they cover well?

For those looking for phosphoric acid at Home-Depot, it also goes by "wood bleach". Not to be confused with TPS however.
TWinbrook7

Offline WEBellSystemChristian

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Re: Phosphoric Acid - Rust Removing Technique
« Reply #3 on: March 17, 2018, 04:50:22 PM »
Wow, how odd. I was just practicing with Oxalic Acid on a phone part. I'm almost finished removing every trace of rust. Take a wild guess what phone part...

...a rusty WE Daisy dial plate! ;D

Mine is in much worse shape than yours was, but the results were still pretty decent. I'll post the before and after pictures once it's finished.
Christian Petterson

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Offline WEBellSystemChristian

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Re: Phosphoric Acid - Rust Removing Technique
« Reply #4 on: March 17, 2018, 06:23:26 PM »
Al, are you positive that Phosphoric Acid is wood bleach? I'm pretty sure it was Oxalic Acid. Maybe it's a mixture of both.
Christian Petterson

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Offline kleenax

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Re: Phosphoric Acid - Rust Removing Technique
« Reply #5 on: March 17, 2018, 07:18:25 PM »
How do those paint pens hold up? Do they cover well?

The oil-based Sharpies cover a LOT better than the water-based pens. On the chipped porcelain, I usually lay it perfectly flat and "pool" the paint in the chip a little to get better coverage. Takes a lot longer to dry, but it does look better.
Ray Kotke
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Offline WEBellSystemChristian

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Re: Phosphoric Acid - Rust Removing Technique
« Reply #6 on: March 17, 2018, 11:06:04 PM »
Here's my bezel after Oxalic Acid (if you don't mind, Ray):

The face wasn't bad as far as rust goes, but the edges were horrible. The edges leaked rust onto the face, and rust started forming on the back as well.

I used a small bucket of water with a couple clumps of Oxalic Acid. It sat overnight and for most of the day today, so it took awhile, but the results were great! I used Brasso with 0000 steel wool to knock down the remaining pitted steel, and polished/waxed the face and bare metal spots.
« Last Edit: March 17, 2018, 11:18:04 PM by WEBellSystemChristian »
Christian Petterson

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Offline kleenax

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Re: Phosphoric Acid - Rust Removing Technique
« Reply #7 on: March 18, 2018, 12:01:00 AM »
Here's my bezel after Oxalic Acid (if you don't mind, Ray):

The face wasn't bad as far as rust goes, but the edges were horrible. The edges leaked rust onto the face, and rust started forming on the back as well.

I used a small bucket of water with a couple clumps of Oxalic Acid. It sat overnight and for most of the day today, so it took awhile, but the results were great! I used Brasso with 0000 steel wool to knock down the remaining pitted steel, and polished/waxed the face and bare metal spots.
Worked very well! 
You know, I can't say that I have ever seen a daisy wheel with all of the RED numbers worn off like that! It's usually just the "1" that is totally worn off; I guess because ALL numbers pass it on their way to the finger-stop!
Ray Kotke
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Offline WEBellSystemChristian

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Re: Phosphoric Acid - Rust Removing Technique
« Reply #8 on: March 18, 2018, 12:32:38 AM »
Worked very well! 
You know, I can't say that I have ever seen a daisy wheel with all of the RED numbers worn off like that! It's usually just the "1" that is totally worn off; I guess because ALL numbers pass it on their way to the finger-stop!
This phone was in a flood--or at least under water--at some point, so rust and water damage seem to be a common theme here. The red letters must have been washed off while sitting in water, but you can still see the dull outline of where they were.

You can see part of "4" where a paint drip was before the acid dip. That paint protected the letter enough to leave behind a gray ghost.
« Last Edit: March 18, 2018, 12:36:21 AM by WEBellSystemChristian »
Christian Petterson

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Offline AL_as_needed

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Re: Phosphoric Acid - Rust Removing Technique
« Reply #9 on: March 18, 2018, 01:13:15 AM »
Al, are you positive that Phosphoric Acid is wood bleach? I'm pretty sure it was Oxalic Acid. Maybe it's a mixture of both.

It could be a mixture or a "safer" version, im sure any strong acid would have that affect on most wood. Phosphoric Acid is also great to clean or etch cement for painting.
 I think oxalic acid is also used in removing plamters worts.(?)  ;D

White vinigar works well with rust removal as well if your unable to use a well bented space.
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Offline kleenax

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Re: Phosphoric Acid - Rust Removing Technique
« Reply #10 on: March 18, 2018, 11:01:16 AM »
White vinigar works well with rust removal as well if your unable to use a well bented space.

I HATE the smell of vinegar, so I never EVER use it!
Ray Kotke
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Offline AL_as_needed

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Re: Phosphoric Acid - Rust Removing Technique
« Reply #11 on: March 18, 2018, 08:28:50 PM »
I HATE the smell of vinegar, so I never EVER use it!

Compared to some of the smells and small scale biological hazards I have inadvertently created in the name of my hobbies, vinegar at least wont burn out your lungs  :P But yes, its no dozen roses either...
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