Mineral oil bad for leather? Or good? Or neutral?

[SUP]

In continuation of the attempt to remove the rancid smell  from the leather bag, I tried the baking soda but not for too long as I was worried it would irreversibly damage the leather. I then applied pure D-limonene on it, in one section, left it on for a minute, then cleaned it out. I cleaned it out with my all purpose cleaner of which D-Limonene is an ingredient. Once wiped, I let it dry. This was about a week ago. I cleaned a second section 4 days ago. Both sections are still free of the rancid smell, so I live in hope.

I will report here on how effective D-Limonene is in removing rancid smells from leather and the condition of the leather at the end of it.

This is  sidetracking a little from the original aim of this thread but since rancidity was a concern when starting it, I though this is the correct place to record this as well.

In an aside, there is talk of mineral oil being occlusive. So is petroleum jelly (more so, in fact) and waxes and butters that people swear by, as well as other oils. The occlusive nature is what preserves the leather and keeps it soft and supple. Else it would dehydrate pretty fast.

All those companies online which cleverly knock down everything but what is in their own products are a bane. People parrot what is said without realizing this and a myth is born and myths are far more persistent than truth.

Another is that mineral oil 'chases' out other oils from leather fibres. Since Mineral oil mixes well with other oils, I wonder how that is possible.  

[fredk]

What was the cause of the rancid smell?   Can we replicate the conditions?

The only time I ever encountered a rancid smell was when one of my historical presentation group (HPG) brought me a belt pouch which he had smeared chicken fat over. 'Cos thats what they would have used in medieval times' quote he. Nothing I could do at the time could save that pouch. It was not only rancid but the thread was rotting away. As it was cheap pouch we binned (trashed) it and I made him a new one FOC and told him to keep way from chicken fat

I think it was Winston Churchill who said 'A lie gets halfway around the world before the truth has a chance to get its pants on'. Even more so with internet and social media and 'influencers' 

 

[SUP]

28 minutes ago, fredk said:

A lie gets halfway around the world before the truth has a chance to get its pants on'. Even more so with internet and social media and 'influencers

Unfortunately!

About what caused the rancidity, I have no idea. She said she used some oils, one of which was olive oil. I think she feels awkward to tell me more.  It could be animal fat for all I know. 

I wonder whether,  if we take a piece of leather and douse it repeatedly in a mix of oils, we might get there. But none of the oils we have used have gone rancid. So I really wonder which ones would get that result.

It is possible that it is the excess of oils rather than a particular oil that caused the problem. In our experiment, we did not over-oil. We oiled the leathers judiciously. So the oils are well absorbed and not overly exposed to air and light for rancidity to result. But if there is too much of it, then it will stay on the surface and top layers and get exposed and go rancid and smell, I suppose. Also, this seems to be oil tanned leather - so already oil-stuffed. Adding more oil on top of that probably made it worse. 

Maye a piece of oil tanned leather soaked in oil and left out in light and air might get the same smelly  result.

I have plenty of oil tanned leather. I will try that once it stops raining. I an wondering which oil or oils to use. 

[fredk]

We are checking the oils for racidity et cetera; but they are all coated and left in the air/weather. My friend's pouch was kept in a closed box with his kit. Although it was brought out at weekends it was mostly stuffed in a box

I'm going to try chicken fat on leather and keep it sealed up in a plastic box. The box will be opened occasionally to sort-of replicate the conditions his pouch was kept in. 

If I can get enough small plastic boxes, and somewhere to put them (!) I'll do the same for some of the other oils/fats

I shall presume the chicken fat came from a cooked chook.  mmmmm. time for roast chicken, yummmy

[SUP]

Oh! I did not think of that! The bag was kept carefully stored inside as well. But from what I read everywhere, exposure to air and oxidation causes rancidity. The periodic opening of the container probably provided additional air and oxygen. I wonder if oxidation happens because of exposure but the results of oxidation remain close to the leather in the enclosed environment and get absorbed into it. Leather is notorious for absorbing smells. Ergo the unpleasant smell of 'old lady bags'. A  bit mean, that. All leather bags get that smell regardless of the age of the owner or the sex.

About animal fats, I know lanolin and tallow do not go rancid, at least not easily. Neither do neetsfoot oil and mink oil. So raw chicken fat? is that how you will use it? Rendered and then applied? After separating from the roast chicken-to-be?

Small individual  boxes is a good idea. Should get some from Temu or Amazon Vine if I am lucky. The controls will be similar pieces kept out in the open.

I am thinking of trying it on both veg-tanned leather as well as veg tanned oil tanned leather this time. Need to check if any of my stock belongs to the latter category.

I will try to note where I got the leather from as well, especially the oil tanned leather. I bet the oils and fats used differ everywhere.  

 

Edited March 16 by SUP

[YanaG]

On 3/6/2025 at 4:57 PM, SUP said:

Oh. I didn't know that. And your leathers are fine, are they not? With the mineral oil based treatments? 

It's a bit a recent situation. Before 2022 a lot more was available, now some things are either very expensive or just not sold anymore. I've only been working with leather for a year, still figuring out leather treatments process for myself.

[SUP]

I have been looking up the ingredients and SDS of many leather products and a major proportion have mineral oil or some other petroleum derived products and no harm done. The products advertise the presence of beeswax and other oils and butters which are usually in smaller proportions, banking on the fact that most people do not even know to look at SDS sheets or even read ingredient lists! 

What have you experimented with up to now, if I might ask?

[YanaG]

I've tried quite a few thing out of curiosity. For the most part I think I use mink fat. I used to work with cheap leather(our leather market is not like yours, lol) a lot in the beginning, fat does a great job of 'filling' it. There are oils sold as neatsfoot, but you get these in unlabeled jars so it's impossible to say what's the oil really. Some sellers will tell you it's a 'compound', some won't. I bought a few from different sellers, they work, you know, oil is oil.  You can get Fiebing's products(pretty expensive if you need a significant amount), there're european brands like Kenda Farben that are widely available. They have different kinds of creams and finishes, tried some of these. I'm using CDM compound and oil right now.

[SUP]

Neetsfoot oil compound has, I believe, mineral oil or something similar added to it.

I guess you will get different brands in Europe and not the same ones here. No reason why they should not work though. Oils and waxes and the petroleum products added to them are the same the world over! There will surely be good ones amongst them. I like the way you are going about it, trying different ones. It's the best way, isn't it?

CDM compound is Neetsfoot oil compound, isn't it? 

CDM oil seems to be something similar. Do you know what the difference is?

 

[YanaG]

Yeah, exactly, pretty much everything marketed here as 'neatsfoot' has different ratios of mineral oil added. 

There's a difference in target market, I imagine. You guys have a lot of people making tack and saddles, here, not so much. And most of those who do use chrome or combi tanned leather with top finishes. Generally leathercraft here is mostly all kinds accessories, so a lot of european products are marketed specifically for shoes, purses and so on and not something I'd use on tack. 

CDM compound and oil are fairly similar, Leather Oil is heavier in terms of conditioning and viscosity. 

A lot of things to try, definitely. 😃