B&W Reversal Bleach — Hydrogen Peroxide/EDTA/Citric Acid

relistan said:

I have pure EDTA here and that's what Kentanghk and I did all the testing with. The amounts for the sodium salts were contributed here by @Anon Ymous . According to this link: https://longkey.com/blog/edta-2na-vs-edta-4na-key-differences/ it looks like the 4na salt has a lot higher pH and that probably should require a fair bit more citric acid to offset it. If it turns out you need a lot more, I'd be happy to update the blog post for this case! I think you're going to need to be able to measure the pH yourself (as you said). If the strips don't work out, the fairly cheap pH meters from Amazon have worked fine for me. If you overshoot the pH and get it a lot too low, you get little to no bleaching as well. It's important to be about right. Hopefully you can measure it with the new strips. Please let us know what you end up with. Good luck

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Raghu Kuvempunagar said:

Check your Peroxide. It needs to be fresh to be effective as a bleach at as low a concentration as 3%. It deteriorates in storage over time.

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artyfarty said:

Thanks, i'll try testing it. Since it was propely packed etc i wasn't expecting any damage. BTW i can buy 30%, 40% or even 50% peroxide here, if it makes things simpler (it certainly would be cheaper

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relistan said:

This bleach is a very effective bleach at 3% peroxide at room temperature. So you won’t need higher concentrations. That was one of the criteria we set. But, if you are doing further experimentation on your own it could be helpful. However, peroxide is quite a strong oxidizer and even less than 3% would probably work if you have the time and inclination to further refine it. When we got to where it worked well repeatably, we stopped.

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artyfarty said:

I checked out precautions for higher peroxide concentrations and it looks like a huge NOPE for me (thanks for the warning), so i'll stick with this recipe until it works.. I'll try one more time with ph strips and edta-4na and better sodium bicarbonate, if it doesn't work out i'll try with pure EDTA, it seems i found one.

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artyfarty said:

Hey again.

Today i tried again with pure sodium bicarbonate and PH strips. I was using automatic stirring in this and previous attempts. I added peroxide, EDTA-4Na, stirred for a minute, added sodium bicarbonate, observed bubbling, stirred for about 5 mins and proceeded with the citric acid.

I started with 5g of citric acid (rightmost strip) that yielded 6+ph. Then i added 6 more up to recommended 11g of citric acid and got a strip very close to ph 5.
Then I iteratively added 2g, stirred, measured and tested effectiveness. I slowly reached ph 4 at total of 19g, but it still didn't work. Then i stopped.

I can see three possible answers:
* EDTA-4Na option has some unforseen complications and doesn't work that easily
* My peroxide is crappy. I don't have easy way to test it and finding peroxide test strips isn't that easy
* I'm mixing and stirring in fundamentally wrong way somehow, because i'm definetly not a chemist

Next i'll wait for pure EDTA to arrive and try with it. If it fails too, i'm blaming peroxide. Probably i'll order from another supplier, or just buy one from pharmacy...

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relistan said:

Does your automatic stirrer heat the peroxide? It may be breaking it down. One simple test for peroxide is to find some zinc and add it to a small amount. Note that this is destructive. A _galvanized_ nail or similar should work. Be sure it’s zinc. If you don’t get bubbling on the surface of the zinc within a short time, the peroxide is probably bad. That won’t tell you very well how strong it is, but it will tell you If it’s pretty exhausted.

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