pre-neutralised vinegaroon

[Nny]

Hi everyone,

I am commencing a few initial experiments with vinegaroon, and I wondered if anyone had any experience with a few ideas

The darkening process of vinegaroon, as I understand it, is due to the reaction between iron (II and III) acetates and the tannic acid in vegtan leather.  the role of vinegar is simply to dissolve the iron into a solution of ferric and ferrous acetate salts.  If this is the case, it should be possible to pre-neutralize the vinegaroon using either baking soda or perhaps hydrogen peroxide (potential side formation of insoluble iron carbonate and iron hydroxide precipitates should be easily removed by filtering, and should not remove too much iron acetate before neutralizing the solution as long as most of the remaining acetic acid has already reacted with iron.  A pH meter or universal indicator paper could be used to gradually titrate the solution towards neutral before using to dye leather

This pre-neutralized vinegaroon should not overly acidify the already acidic leather, removing the need for a baking soda bath and avoiding the problems with potentially over alkalizing the leather.

There is perhaps an increased potential for the solution to go mouldy over time (although the high concentration of iron salts should probably prevent this) but if this were a problem small amounts of vinegaroon could be neutralised before use, leaving the bulk solution acidic for storage until needed.

As an initial experiment I pre-mixed a small amount of fresh vinegaroon (on the day I made it) with excess baking soda until the result was definitely alkaline (in fact the result was a paste with unreacted baking soda) and it still dyed the leather black.  I have no doubt I over alkalized the leather in the process, but the point was to confirm that the acidic conditions of the vinegaroon are not necessary for the reaction with the tannins.

I have a batch of vinegaroon maturing and have ordered a pH meter and some indicator paper, and plan to experiment properly in a few weeks, but am wondering if anyone has conducted similar experiments or can comment on my understanding of the chemistry.  Also, if anyone has an idea of a potential base to neutralize the solution which won't precipitate out some of the iron ions, I would be interested.

My hope is that pre-nautralised vinegaroon could be simply be rinsed off, leaving a dyed item that should not corrode metal hardware like snaps and rivets

[JD62]

Interesting I wonder if you could just use distilled water to rust and suspend the iron salts. It would take take longer but so what?

[Nny]

Hi JD,

I believe that vinegar (or some substitute, e.g. HCl) is probably necessary to acheive a black color; something that gives soluble iron compounds which can react with the tannins to give the black iron-tannin compounds. What is needed is soluble iron compounds.

https://chemistry.stackexchange.com/questions/5027/how-does-the-mordant-ferric-acetate-interact-with-tannins-when-ebonizing-wood

 

Rusting iron in distilled water would result primarily in a suspension of solid particles of insoluble iron (II) and iron (III) oxides and hydroxides.  Because these iron compounds are insoluble, they would not present free iron ions to react with the tannins.  Leather can be colored by dipping in rusty water, but the color is brown rather than black (probably a result of the small red/brown insoluble rust particles being absorbed (or adsorbed, it has been too long since my chem days) into the pores of the leather

for example see

http://www.willghormley-maker.com/MakingHOGRig.html

scroll down to the description of the rust tank to see the results of rusty water on leather, lovely but not black.

 

The question of substituting water for vinegar raises another interesting question.  Given soluble iron compounds are needed, there are several options that might work at least as well as vinegar.  Iron chlorides are soluble (as are other halides, but why experiment with flouride, bromide or iodide salts unnecessarily, given the ready availablility of HCl) sulfates (adding extra sulfur salts seems a bad idea) nitrates (might work, but ferric nitrate etches silver so I will give it a miss unless there is some reason not to use acetates). I suppose there may be advantages to using a strong acid (HCl or HNO3) rather than a weak acid like vinegar (acetic acid) - for example reaction time might be hours or days rather than weeks, but vinegar has worked for ages and the question of pre-neutralization is the same regardless of acid used, so I may save that for a later experiment unless someone has relevant experience on this issue which could guide further experimentation

 

[JD62]

You have a good point, I was just thinking of a wet iron clamp turning solid oak black,as any wood worker knows.

[tibee]

I know this is super old but any updates on the pre-neutralized vinegaroon experiment?  

[PhilC]

I'm unfamilar with vinegaroon, but i recently discovered this leather marbling technique that uses potassium carbonate and ferrous sulfate to make really beautiful  marbling patterns on calf leather https://www.hewit.com/skin_deep/?volume=15&article=1.  I am going to try it out soon.  The recipe dissolves ferrous sulphate in water, so it may be applicable to this discussion.