Iron sulphate to colour leather black

[ScottEnglish]

Thanks for your comment dikman. Maybe baking soda would've worked. No, I didn't check the pH of the solution tsunkasapa. In future if I want to colour leather black I'll use vinegaroon!

[Matt S]

 

On 9/30/2023 at 10:56 PM, dikman said:

Maybe should have washed it off with a baking soda solution to neutralize it?

 

On 10/1/2023 at 2:21 AM, tsunkasapa said:

Has anyone bothered to check the Ph of the solution? Here is a quote from Wikipedia;

Iron(II) sulfate is sold as ferrous sulfate, a soil amendment^[20] for lowering the pH of a high alkaline soil so that plants can access the soil's nutrients.

This would lead one to assume that it is an acidic compound, hence needing to be neutralized.

 

On 10/1/2023 at 7:52 AM, ScottEnglish said:

Thanks for your comment dikman. Maybe baking soda would've worked. No, I didn't check the pH of the solution tsunkasapa. In future if I want to colour leather black I'll use vinegaroon!

Apologies for not responding individually -- short of time and sleep and I figure a brusque response is better than none! 

Veg tanned leather is acidic (i.e. it has a pH of 0-7). From memory it needs to have a pH of around 3-4. Changing it very much in either direction can cause premature degradation. If you don't know what the pH of your treated leather currently is, or what pH you want it to be, dumping it in baking soda is like driving a car blindfolded!

I have stuff I blacked with iron sulphate that's years old. Some cracked, some didn't. The stuff that cracked is when I followed the herd advice of "neutralising" in baking soda. The stuff that didn't I just washed it in a couple changes of water, let it dry and applied an appropriate dressing to replace the lost fats and oils.

Unless you're using a tiny amount of baking soda (which is alkaline, with a pH around 8) you're going to bring the pH way too high. Whether you neutralise it to pH7 or completely overshoot and make it alkaline is irrelevant -- if you bring the pH above 4ish you're shortening the life of the leather.

10% iron sulphate in water has a pH of slightly less than 4. That's bang in line with what I'd expect a piece of veg tanned leather to be. If anything I'd say that veg tanned leather treated with iron sulphate might have raised its pH (seeing as some of the tannic acid is "used up" reacting with the iron to make black iron lake) and needs slight acidifying rather than having something like baking soda applied!
 

On 9/30/2023 at 6:45 PM, ScottEnglish said:

The only explanations I can think of are that the solution of iron sulphate powder and water, despite rinsing and soaking the leather in water after colouring it black, was too acidic and some remained in the leather causing it to rot, or that there was a reaction between the remains of the Fiebing's Pro Dye and the solution of iron sulphate powder and water.

I've made several pairs of simple boots before using the same type of leather, natural vegetable-tanned, and never had this problem.

Sorry to hear about your boots Scott. You say you took a pair of dyed boots and struck them with iron sulphate. How else were they treated? Alcohol based dyes can strip a lot of the oils that even "natural" leather has had added. Water based dyes and treatments can affect leather in a similar way. Did you treat them with fat, oil, wax or grease at any point? Veg tanned shoe uppers is unusual these days as other tanning methods tend to produce leathers that are less affected by their environment. Were your black boots worn in the same way as your other boots -- not worn more often or got wet or left in the sun more than the others?

[Littlef]

On 9/30/2023 at 7:21 PM, tsunkasapa said:

Has anyone bothered to check the Ph of the solution? Here is a quote from Wikipedia;

Iron(II) sulfate is sold as ferrous sulfate, a soil amendment^[20] for lowering the pH of a high alkaline soil so that plants can access the soil's nutrients.

This would lead one to assume that it is an acidic compound, hence needing to be neutralized.

Just doing a quick google search I found a ph of 3-4.  of course concentration changes will make that vary, but its definitely acidic.  

[SUP]

Not quite sure why Iron sulphate in water is used. Plain white vinegar with any old iron added gives a gorgeous black color. It takes a few days, no more than 3-4 days, but the results are always wonderful. My first batch I used old, rusted iron nails and that worked fine. Now I use steel wool and that works well too.

I have been using vinageroon for a while now and after a dip in vingaroon I just rinse my leather in running water and let it dry. That is really sufficient I find. It does not stink either - a very mild smell that disappears in a couple of days.

I am always concerned about the pH going too high if I dip in a baking soda solution, no matter how dilute. Vinegar is anyway 5% acetic acid in water, so it just gets rinsed off with a quick wash and  since water has a more or less neutral pH, it balances out the pH perfectly well. A little vinegar remaining would, in fact, maintain the ideal pH of between 4 and 5.

The vinegar is also too dilute to damage the threads used, if rinsed off immediately after a dip.

Some things really are simple, surprisingly so. But that is nice! 

 

 

 

 

[ScottEnglish]

Hi Matt S. Thanks for your informative post. My black boots were treat in exactly the same way as the three other pairs of vegetable-tanned leather boots I made. Only the leather on the black boots is rotting. I've learnt from other members that historically iron sulphate has been used to colour leather black. So we know it works. However, for whatever reason, my own experience has been negative.

Thanks for your comment Littlef.

I'll try vinegaroon in future if I want to colour vegetable-tanned leather black SUP.