Green after acid bath

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Green after acid bath

#1

Post by Nobes1010 »

Put some dumpers in acid for what was probably too long and now they're tinted a light shade of green. Is this permanent? Hahaha.


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Re: Green after acid bath

#2

Post by willssoda »

What kind of water did you use?
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Re: Green after acid bath

#3

Post by DaveNH »

Yup, most likely too long soaking. There’s a little bit of trial and error with oxalic acid in terms of water amount & temp, amount of acid and length of soak. Keep soaking them…
Thanks. Dave
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Re: Green after acid bath

#4

Post by Nobes1010 »

willssoda wrote: Tue Aug 31, 2021 8:54 pm What kind of water did you use?
Hot tap water in an insulated cooler.
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Re: Green after acid bath

#5

Post by Nobes1010 »

DaveNH wrote: Wed Sep 01, 2021 8:44 am Yup, most likely too long soaking. There’s a little bit of trial and error with oxalic acid in terms of water amount & temp, amount of acid and length of soak. Keep soaking them…
Shoot. I took them out and rinsed and dried. Should I re-soak? It will reverse if I keep soaking? Again these are dumpers so not a huge deal. I'm kinda using it as a trial. I put in more than a tablespoon per can because they were quarts, too.
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Re: Green after acid bath

#6

Post by DaveNH »

Unfortunately you can’t reverse the “green tint”. The stats I need are:

1. How much water did you use
2. How many cans did you soak
3. How long approximately did you leave them in the acid
4. How much acid did you use

All these are related one way or another. Glad they are dumpers!
Thanks. Dave
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Re: Green after acid bath

#7

Post by Nobes1010 »

DaveNH wrote: Wed Sep 01, 2021 6:33 pm Unfortunately you can’t reverse the “green tint”. The stats I need are:

1. How much water did you use
2. How many cans did you soak
3. How long approximately did you leave them in the acid
4. How much acid did you use

All these are related one way or another. Glad they are dumpers!
1) Hard to say exactly. It was enough to fill and cover (with about 2 inches to spare) three quart cans
2)
3) Two days (I rinsed after one day and felt it wasn't enough so gave a second bath (fresh acid mix) for another day
4) 6 heaping tablespoons (each time)

Fair to say I overdid it on time and amount of acid, I'm guessing.
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Re: Green after acid bath

#8

Post by mtracy64 »

You'll get widely varying opinions on oxalic usage here. My own opinion is, the only thing I've ever done wrong is leaving cans in too long. I rarely leave anything in more than a few hours unless they're still mystery cans after a few hours. I clean better cans singly in peanut butter jars, using hot tap water and strong acid - I use a heaping tablespoon on a single can, and I have a strong preference for the pure white pharmaceutical grade rather than the brown-ish industrial grade. I like to pull cans out after just a few minutes, rinse under cold water and then brush lightly with a toothbrush while continuing to rinse under cold water, then put them back in. This removes some of the rust the acid has loosened and clears a path for the oxalic to work deeper, plus it limits how much the acid degrades due to dilution. My goal is to be done as quickly as possible, as the effectiveness of the acid lessens as the water cools.

Marc
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Re: Green after acid bath

#9

Post by Nobes1010 »

mtracy64 wrote: Sat Sep 04, 2021 12:15 pm You'll get widely varying opinions on oxalic usage here. My own opinion is, the only thing I've ever done wrong is leaving cans in too long. I rarely leave anything in more than a few hours unless they're still mystery cans after a few hours. I clean better cans singly in peanut butter jars, using hot tap water and strong acid - I use a heaping tablespoon on a single can, and I have a strong preference for the pure white pharmaceutical grade rather than the brown-ish industrial grade. I like to pull cans out after just a few minutes, rinse under cold water and then brush lightly with a toothbrush while continuing to rinse under cold water, then put them back in. This removes some of the rust the acid has loosened and clears a path for the oxalic to work deeper, plus it limits how much the acid degrades due to dilution. My goal is to be done as quickly as possible, as the effectiveness of the acid lessens as the water cools.

Marc
This is fantastic advice. Thank you
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Re: Green after acid bath

#10

Post by plogan42 »

The green you refer to is re-deposition of iron oxalate onto the surfaces of the can.

It is caused by the following:

a) water temperature changing during course of soak
b) too much dissolved iron oxalate in solution
c) soaking can(s) too long in saturated (read: 'Gatorade Green') acid solution)
d) all of the above.

This green haze on cans is typical, but can be minimized and mitigated, as follows:

1) Use room-temperature water for a soak.
2) Use smaller container (clear PET container w. lid is fine - tall Jack Link's meat stick containers are best - perfect for observation during soak).
3) Change out the solution with fresh stock every several hours, once you get to what I call 'Gatorade Green'-colored solution.
Your acid solution at that point is saturated, so it won't pull much more rust off without spreading the powdery green mildew all over your cans, or damaging the paint with over-soaking. So you get more rust dissolving fire-power with fresh solution. Remember, it's not the level of acid in the solution that matters, but the capacity of the solution to absorb iron oxalate. Clear, fresh solution will keep dissolving rust, even hard East Coast concreted rust. 'Gatorade Green' has lost it's rust-cleaning teeth, no matter how much more acid you dose it with. Don't do that. Re-fresh with new solution if you're planning to continue soaking a can, after the water turns green.
4) If you notice the green haze after you've cleaned a can sufficiently, give the can a quick dip in coca-cola (phosphoric acid), rinse, and scrub the seam, lids, rims with a brass wire brush. A little elbow grease while scrubbing will help remove the re-deposition of iron oxalate salts on your cans.
5) If you still don't like the results, tape up the can with paper after it's rinsed and dried, using some painter's masking tape (just don't pull off any paint...), and an aluminum sleeve cut from an empty. Then escalate to using Dremel sanding gear.

But fear not.......the green haze can be made to go away. It's only an iron salt after all, and if we can't lick that, what good are we ?

Good luck and keep cleaning em' !!!!
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Re: Green after acid bath

#11

Post by plogan42 »

Yeah, forgot to mention, hot oxalic solution holds X % dissolved iron oxalate.

As the solution cools, the amount of capacity the solution has to store dissolved iron oxalate, is reduced. So envision, X, less 20%.

So as the solution cools, it chemically forced iron oxalate out of solution, and because of the electrical charge of the can in solution, re-deposits this iron salt back on the can to all exposed (unpainted) surfaces.

It's another reason to avoid using hot oxalic solution, the primary reason is to save the paint. Always save the paint, otherwise what's the point of trying to clean a can.
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Re: Green after acid bath

#12

Post by plogan42 »

Another alternative to remove green staining:

Dab a wadded-up paper towel in a dish of bleach, and begin wiping the green staining (iron oxalate staining). Get the spot wet w. the a little bleach, and keep gently rubbing. You'll notice the bleach-wet paper towel turns orange-brown. It's breaking down the iron oxalate staining by turning the iron in it, back into soft rust. A quick (1 min.) re-dip in clean oxalic (or citric) solution afterward will dissolve any 'rust' that the bleach creates where the green staining is. Several rounds of this treatment will get rid of iron oxalate staining, but it can be a slow-process, so be patient. When done, soak can in clean water mixed with some baking soda (to neutral acid treatments). This should last for 5 minutes or so. Afterwards, then wash/rinse again with soap and water, and you should be done.

Changing the water often when soaking out the cans in the first place, will prevent dealing with the follow-up (green) staining. So that really is the solution to it.
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Re: Green after acid bath

#13

Post by iggyks »

The discussion of the oxalate reattaching made me wonder if anyone has tried electrolysis on cans. It's popular among metal detectorists for relics but of course that is on rusted bare metal.
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Re: Green after acid bath

#14

Post by willssoda »

Probably staining from acid but blue/green can also be copper which could be coming from your water source. I would recommend using purified water when soaking. Purer the water the better the results from the acid( less to compete with. More minerals in the water the more acid you'll need to get the same result. Aquaphina/ RO or distilled water would be best. You could try some citric acid or lemon juice to see if it will remove the green staining.
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Re: Green after acid bath

#15

Post by plogan42 »

No, it's not caused by copper in the water.

The yellow-green staining is iron oxalate, which results as a buildup on cans from oversoaking in saturated oxalic acid solution.

It can come off fairly easy with alternating treatments of cotton balls/tweezers/bleach. Dab the yellow spots with the wet cottonball, and rub it a little. It converts the iron oxalate to iron oxide (II), which easily comes off with cotton balls/tweezers/citric acid + water solution. You'll notice using the bleach-soaked cotton balls that plenty of orange colored rust is removed. This is the bleach oxidizing the iron oxalate into iron oxide. Alternate with citric acid-soaked cotton balls next.

A couple application back and forth using the bleach, then the citric solution, will rid your cans of the greenish, yellow haze that results from iron oxalate buildup on cans previously soaked too long in dirty oxalic acid solution.

Electrolysis will destroy the can. Don't do that. Very bad. Very bad.
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Re: Green after acid bath

#16

Post by Bob L »

Agree on the deposition of the oxalate onto the can. There is also another well-documented phenomenon that occurs. If you clean your cans in direct sunlight, whether in an open-top container or even in a clear-sided container, the green film will form aggressively, even with fresh acid solution. I don’t begin to understand the chemistry behind this or how sunlight drives it, but perhaps it also involves the deposition of the oxalate back onto the metal in some way. This effect has been confirmed by many guys over the years that clean a lot of cans. Always do the cleaning out of the direct sunlight or use an opaque container, sides and top.

I use an old cooler for can cleaning, because it helps keep the acid solution warm longer.
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Re: Green after acid bath

#17

Post by plogan42 »

Bob L.

Yes, sunlight is bad while soaking using oxalic.

Another factor is change in temperature of water.

Reason I don't use hot oxalic solution unless I'm in the woods and have an old pot on a camp fire to heat water to see what mystery cans I've bumbled upon.

Room temperature water for home cleaning is best as there is less temperature variation. Temp. variation of solution caused iron oxalate (Gatorate) to fall out of solution (precipitate) as it cools. Using room temp water helps prevents that over short intervals.

But to avoid the GREEN, swap out the water as soon as it turns into a Gatorade-looking solution. This will prevent iron oxalate buildup 99% of the time. One just burns up lots of acid that way, but it's worth it. Getting cheap bulk acid on Ebay makes the cost factor, an immaterial concern.

Sellers of 'wood bleach' on eBay are generally cheaper than sellers of chemical oxalic acid.

Good luck.
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