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Hi all! I did an experiment yesterday by putting a pH indicating dye on a strip of maple. I let that dry, and then applied 5% sodium nitrite solution to it, and placed it in the light box. To my surprise, only after a few minutes of light exposure the dye changed from orange to a cool red, indicating the presence of a base. I had always thought that nitrite reaction produces nitric acid, so, I’m very confused as to why this test indicates as alkaline. Anyone have a possible explanation? Also, I’m wondering if this is a good approach to create a pH neutral treatment? I’m not a chemist, but I imagine one could find the proper salts to add, to make sure the dye does not change color through the process. 

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The effects you're seeing on the pH strip is only occurring on the pH strip, not the wood, because pH strips are an indication of hydrogen ions which can only be measured in a solution. My guess is that the UV spectra is having an effect on the chemical reaction that alters the color of the pH indicator.

Edited by Jim Bress
Spell check demon changed hydrogen to nitrogen
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6 minutes ago, Jim Bress said:

The effects you're seeing on the pH strip is only occurring on the pH strip, not the wood, because pH strips are an indication or nitrogen ions which can only be measured in a solution. My guess is that the UV spectra is having an effect on the chemical reaction that alters the color of the pH indicator.

@Jim Bress hi Jim! I think there must be a misunderstanding, I did not use a ph indicator strip. I dyed the wood Itself, with a ph reactive dye. And I have tested the dye with UV alone, and it is extremely lightfast. But yes, I suppose something else may be causing it to change color

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I spent 34 years as a chemist. If you haven't actually measured the pH, you can't make assumptions. Sodium Nitrite is an oxidizer, and it's very possible that you are oxidizing the dye to a different color rather than it acting as a pH indicator. It's also possible that as  the nitrite reacts, it might form Sodium Hydroxide as a byproduct.

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If you irradiate nitrite(aq) with UV light  ,you generate OH_ ions. If you irradiate nitrate (aq) you will produce nitrite  ions.  A lot depends on the wavelength of the UV.

To the OP, most indicator solutions produce a red colour due to H+ (acidic) presence not bases, bases are usually blue purple colours.

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1 hour ago, fiddlecollector said:

If you irradiate nitrite(aq) with UV light  ,you generate OH_ ions. If you irradiate nitrate (aq) you will produce nitrite  ions.  A lot depends on the wavelength of the UV.

To the OP, most indicator solutions produce a red colour due to H+ (acidic) presence not bases, bases are usually blue purple colours.

Thank you. Can you explain to a non-chemist how the UV interacting with nitrate or nitrite produces the colour in the wood?

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That may be correct. I remember I saw some studies done on rabbits that show that presence of NANO2 in blood and application of UV causes relaxation. Relaxation is typically result of presence of nitric oxide as product of NANO2.

But what does the rest do I have no idea.

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15 hours ago, Jeffrey Holmes said:

Pardon me for my questionable memory of my chemistry classes, but if I recall correctly NaNO2 is a weak base, and when exposed to UV, nitric oxide is released (which is a neutral). If I'm off, those with a more thorough knowledge on the subject please correct and enlighten me.

Yes your right a weak base and does produce nitric oxide .Nitric oxide is a free radical and rapidly reacts with any oxygen present . It will produce nitrous acid if water is present.

Back to the original question,  of why it colours wood.Oxidation is just one reason. Its too difficult to give a simple answer as there is probably hundreds of little reactions going on at the same time  . Its not like reacting one chemical with one other one. Its like adding one chemical  to a bucket load of mixed chemicals .

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4 hours ago, fiddlecollector said:

 

Back to the original question,  of why it colours wood.Oxidation is just one reason. Its too difficult to give a simple answer as there is probably hundreds of little reactions going on at the same time  . Its not like reacting one chemical with one other one. Its like adding one chemical  to a bucket load of mixed chemicals .

Thanks. I guess it can't be just oxidation. Expose a white violin to just UV in air, and it darkens to a pretty uniform color. Apply nitrite and the spruce and maple color differently. 

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On 12/20/2020 at 5:46 AM, fiddlecollector said:

If you irradiate nitrite(aq) with UV light  ,you generate OH_ ions. If you irradiate nitrate (aq) you will produce nitrite  ions.  A lot depends on the wavelength of the UV.

To the OP, most indicator solutions produce a red colour due to H+ (acidic) presence not bases, bases are usually blue purple colours.

Ah, that is interesting to read! I learned a bit more about why nitrates and nitrites are the ph, that they are, and I find it interesting that very few people mention using Sodium and Potassium nitrATE, even though they are neutral in solution. Also, I believe in Helen Michetschlager’s analysis of Koen Padding’s primers, there were many nitrATES, including ammonium nitrate, which would seemingly break down forming ammonia gas as a byproduct. That sounds better than leaving alkali salts behind in the wood....

I’ve noticed that oxidizers tend to tan more red in UVA, and more green in UVB and I’ve wondered if the greenish cast came from some sort of alkaline reaction, similar to the green undertone you get from ammonia fuming. Though I’ve also noticed that dampening the wood before ammonia fuming  tends to lead to a nicer, less green/ more gray look. So many variables! Enough to keep me interested for a long time haha

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  • 4 weeks later...
On 12/19/2020 at 7:04 PM, FiddleDoug said:

I spent 34 years as a chemist. If you haven't actually measured the pH, you can't make assumptions. Sodium Nitrite is an oxidizer, and it's very possible that you are oxidizing the dye to a different color rather than it acting as a pH indicator. It's also possible that as  the nitrite reacts, it might form Sodium Hydroxide as a byproduct.

This is my assumption too.

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On 12/20/2020 at 12:19 AM, Michael_Molnar said:

Purchase a pH meter if you are serious. Indicator papers were for your grandparents.

this would rquire to wash the wood and see a tiny change in pH of the wash solution. You can't use a pH meter on a surface.

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On 12/21/2020 at 5:45 PM, Marcus Bretto said:

Ah, that is interesting to read! I learned a bit more about why nitrates and nitrites are the ph, that they are, and I find it interesting that very few people mention using Sodium and Potassium nitrATE, even though they are neutral in solution. Also, I believe in Helen Michetschlager’s analysis of Koen Padding’s primers, there were many nitrATES, including ammonium nitrate, which would seemingly break down forming ammonia gas as a byproduct. That sounds better than leaving alkali salts behind in the wood....

I’ve noticed that oxidizers tend to tan more red in UVA, and more green in UVB and I’ve wondered if the greenish cast came from some sort of alkaline reaction, similar to the green undertone you get from ammonia fuming. Though I’ve also noticed that dampening the wood before ammonia fuming  tends to lead to a nicer, less green/ more gray look. So many variables! Enough to keep me interested for a long time haha

There's been several different formulations going around since the analysis of KP's primers, and I've tried 4 different recipes with various salts as well as nitrites and nitrates. I'm sure there are others that haven't passed my way, but I have to say I can't detect that any of the ones I've tried give very different results than a plain old nitrite solution. Maybe my color perception isn't as finely honed as some...

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3 hours ago, uguntde said:

this would rquire to wash the wood and see a tiny change in pH of the wash solution. You can't use a pH meter on a surface.

I did not realize you were trying to test a surface. The paper will tell you if there is an excess of acidic or basic surface chemicals. 

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