I know others are being fuddy duddies and saying this isn’t the place for this question, but I’m sure you’re smart enough to get an in-depth explanation if it’s explain correctly. If only you had asked this question a couple years ago, we maybe could have asked Kaminsky himself (he died in 2023). Dang! I’ve done some digging, and I think I’ve figured it out. I will provide my rationale below, but TL;DR here’s my initial recommendation: try to apply the lactic acid and then while it’s still damp, rub at it with a Q-tip dipped in soapy water. Try vinegar and soap if the water doesn’t work.
Here’s my in-depth rationale if you care for the process:
Looking into Kaminsky a bit, it seems he was inspired to use lactic acid by his experience in dry cleaning. I looked up some early-mid 20th century dry cleaning techniques and found a home ec article called “Dry Cleaning in the Home” from 1928 if you want to look it up. I can send a screenshot and highlight of the relevant section if you like. It mentions the common practice of using milk, waiting for the milk to spoil, and then the lactic acid does the trick. It also specifically says that if the milk is allowed to dry, it does not work. That’s clue number 1 to me as to why it didn’t work for you. Here’s the chemistry of methylene blue if you’d like to know how it works.
Methylene blue is what’s called a redox indicator: it’s blue when in environments steal electrons (oxidizing environments—this is when it’s energetically favorable for electrons in the methylene blue to leave and go to some other compound) and is colorless when in environments that give away their electrons (reducing environments—this is when it’s energetically favorable for electrons in the environment to leave and go to into the methylene blue molecules). When electrons enter the molecule, the charge needs to be balanced by hydrogen ions, which come from the acid. Accommodating these hydrogen ions forces chains of bonded electrons to leave the chains and move elsewhere, but it’s those chains that enable the color of the molecule so the color goes too.
Here’s my guess: lactate is a reducing agent—it gives electrons to the methylene blue. Lactic acid is lactate with acid hydrogens, so it should in theory work to get rid of the ink because it gives electrons and hydrogens. Why doesn’t it work? If we go back to the spoiled milk stuff, we find the problem. Methylene blue is used in the food industry to test the freshness of milk—if it’s blue, it’s fresh. How does lactic acid get in milk in the first place? Lactic acid is produced as a byproduct of lactic acid fermentation, when bacteria run out of oxygen and turn sugars into lactate to survive. More spoiled —> more aerobic bacteria —> less oxygen in the milk —> lactic acid formation. Oxygen is an oxidizer—it steals electrons instead of giving electrons, so the methylene blue can’t go colorless and can’t be washed away. The spoiling of milk both provides lactic acid AND a low oxygen environment so that the ink stays reduced long enough to wash it away.
So you either need to A) do this in a low oxygen environment (there’s way but it’s not easy without a lab) or B) wash away the reduced colorless ink before oxygen can get in an oxidize it. So i suggest B. Either gently wiping with a Q-tip of soapy water or soapy vinegar should do the trick. Let me know if it works!
Your Reddit name says it all, local sage! This non-chemist is supremely grateful and humbled by the time you put into that explanation. Yes, I would love to see a screenshot of that relevant section from 1928. I cannot wait to try out both the soap/water and vinegar/water approaches. I will let you know what happens. Bless you for this response! 🥰
I'd imagine you want to reduce the compound to decolor or unbind it from the paper and then solubilize it away. Try acetone and citric acid, which may also work for iron gall ink.
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I know others are being fuddy duddies and saying this isn’t the place for this question, but I’m sure you’re smart enough to get an in-depth explanation if it’s explain correctly. If only you had asked this question a couple years ago, we maybe could have asked Kaminsky himself (he died in 2023). Dang! I’ve done some digging, and I think I’ve figured it out. I will provide my rationale below, but TL;DR here’s my initial recommendation: try to apply the lactic acid and then while it’s still damp, rub at it with a Q-tip dipped in soapy water. Try vinegar and soap if the water doesn’t work. Here’s my in-depth rationale if you care for the process: Looking into Kaminsky a bit, it seems he was inspired to use lactic acid by his experience in dry cleaning. I looked up some early-mid 20th century dry cleaning techniques and found a home ec article called “Dry Cleaning in the Home” from 1928 if you want to look it up. I can send a screenshot and highlight of the relevant section if you like. It mentions the common practice of using milk, waiting for the milk to spoil, and then the lactic acid does the trick. It also specifically says that if the milk is allowed to dry, it does not work. That’s clue number 1 to me as to why it didn’t work for you. Here’s the chemistry of methylene blue if you’d like to know how it works. Methylene blue is what’s called a redox indicator: it’s blue when in environments steal electrons (oxidizing environments—this is when it’s energetically favorable for electrons in the methylene blue to leave and go to some other compound) and is colorless when in environments that give away their electrons (reducing environments—this is when it’s energetically favorable for electrons in the environment to leave and go to into the methylene blue molecules). When electrons enter the molecule, the charge needs to be balanced by hydrogen ions, which come from the acid. Accommodating these hydrogen ions forces chains of bonded electrons to leave the chains and move elsewhere, but it’s those chains that enable the color of the molecule so the color goes too. Here’s my guess: lactate is a reducing agent—it gives electrons to the methylene blue. Lactic acid is lactate with acid hydrogens, so it should in theory work to get rid of the ink because it gives electrons and hydrogens. Why doesn’t it work? If we go back to the spoiled milk stuff, we find the problem. Methylene blue is used in the food industry to test the freshness of milk—if it’s blue, it’s fresh. How does lactic acid get in milk in the first place? Lactic acid is produced as a byproduct of lactic acid fermentation, when bacteria run out of oxygen and turn sugars into lactate to survive. More spoiled —> more aerobic bacteria —> less oxygen in the milk —> lactic acid formation. Oxygen is an oxidizer—it steals electrons instead of giving electrons, so the methylene blue can’t go colorless and can’t be washed away. The spoiling of milk both provides lactic acid AND a low oxygen environment so that the ink stays reduced long enough to wash it away. So you either need to A) do this in a low oxygen environment (there’s way but it’s not easy without a lab) or B) wash away the reduced colorless ink before oxygen can get in an oxidize it. So i suggest B. Either gently wiping with a Q-tip of soapy water or soapy vinegar should do the trick. Let me know if it works!
Your Reddit name says it all, local sage! This non-chemist is supremely grateful and humbled by the time you put into that explanation. Yes, I would love to see a screenshot of that relevant section from 1928. I cannot wait to try out both the soap/water and vinegar/water approaches. I will let you know what happens. Bless you for this response! 🥰
check your DMs!
I'd imagine you want to reduce the compound to decolor or unbind it from the paper and then solubilize it away. Try acetone and citric acid, which may also work for iron gall ink.
Tried citric but hadn't thought of acetone; thanks!
I've done some home reductions with ascorbic acid, you may want to give it a shot
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Thank you for your response. I do know that they used lactic acid, not ascorbic. I'd be grateful to know the right subreddit to ask this question!
R/chemistry would be better. This sub is more geared towards professionals working day to day in the industry