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

[SUP]

The 2nd part of the experiment:

This has leather pieces soaked in one of the following:

Lanolin

Tallow

Cod liver oil

Mixture of mineral oil and coconut oil

Smoothness: In this set, the pieces treated with the oils, whether cod liver oil or the MO-CO mix, for the most part, are smoother and softer than the ones treated with Lanolin or tallow, although only marginally so. But it is seen across all the locations.  However, in spite of being smoother, they feel a little more dry than the leather treated with  Lanolin or Tallow.

Shape: The lanolin treated leather maintained its shape the most across locations, closely followed by tallow. The leather treated with the oils showed a small amount of warping. This is a slight change, but it is present in the leather in all locations.

Stiffness: The leathers treated with tallow and lanolin showed a slightly greater degree of stiffness than the ones treated with oils. The cod liver oil produced slightly more stiffness than the MO+CO  which produced barely any stiffness at all.

Smell: None of the products used maintained their smell. The smell of lanolin, tallow, cod liver oil and coconut oil are completely absent in all the leather pieces, across the board.

 

The pieces kept outside showed significantly mor darkening, drying and stiffness than any other pieces.

The darkening was very similar across all treatments, being marginally more in the CO+MO treated piece. The dryness was similar across treatments as well, as was change in shape  but Lanolin did not cause any change in shape at this point. All the treatments produced slight stiffness except for the MO-CO mix. That piece of leather is still soft and pliable.

The smells of the Lanolin, Tallow, Cod liver oil and Coconut oil are completely absent in all the pieces.

 

The following information is mainly about the leather pieces kept in locations other than outside:

The leather pieces treated with Lanolin have maintained their flat shape across locations. They are less dry than the oil treated leathers although they do not feel as smooth. The difference is slight but present in all locations. They are also slightly more stiff than the oil treated leathers, although less than the Tallow treated ones.

Tallow has made the leather pieces stiffer than any of the other products. The pieces have darkened slightly as well and are the stiffest of all the pieces in the different locations. They have maintained their shape for the most part, except in the outdoors sample.

Cod liver oil has darkened all the pieces slightly and uniformly in all locations, significantly more in the outdoors sample. The pieces are all holding their shapes reasonably well although less than any of the pieces treated with Lanolin Tallow or the MO+CO mix. The pieces are also slightly dry and slightly stiff.

MO+CO: These pieces darkened slightly and show some extent of dryness, the extent depending on the location, but they remain soft and pliable and are holding their shapes reasonably well. The dryness and color change is comparable to cod liver oil but the latter pieces show a slight change in shape in all the locations that is much less in the CO+MO.

 

Mineral oil and Petroleum Jelly for water resistance - a short report this time.

My 2nd leather piece treated with petroleum Jelly (PJ)+Mineral oi (MO) seems to have disappeared as well.

All the pieces remained outside, in the heat initially, then rain and freezing temperatures.

They are all, pliable and reasonably soft. They are all also very dark, the MO and the MO+PJ treated ones more than the PJ treated ones.

I kept a drop of water on each of the pieces and waited.

The Control absorbed the water at once.

The MO treated one absorbed the water in about 2 minutes.

The leather piece treated with MO+PJ has the water droplet unabsorbed 10 minutes later, but the edges may be slightly fuzzy.

The water droplets on the leathers treated with only PJ seem to show the greatest water resistance- the water is completely unabsorbed, edges clear.

A half hour later, astonishingly, the water drops on the PJ treated ones are getting gradually absorbed and are flat now but the droplet on the PJ+MO one, is still virtually unabsorbed.

So clearly, PJ provides good water resistance on leather. When put together with MO, it might work better. However, since I have only one sample for this, I will need to test this on more samples.

But it is promising.

Edited January 31 by SUP
Missed adding 2nd photograph.

[fredk]

[fredk]

We have now done 16 months of testing. (October '23 to end of January '25)

All the pieces are much the same as on June 6th 2024, with only some slight changes on a few pieces

Set #1, the Car set

1. Baby Oil; Both sides are dark, slightly lighter on the reverse side, More flexible than Control 1 (C1), No smell,  No sign of rot or fungus

2. Cooking Oil (rape seed);   Both sides very dark, Slightly more flexible than C1, Stronger cooking oil smell, No sign of rot or fungus

3. Lard (pork fats);  Light but darker than C2, Flex is about the same as C1,  No smell, No sign of rot or fungus

4.  NFO Compound; Both sides very dark,  Flex is better than C1, No smell, No sign of rot or fungus

5. Olive Oil ( Pure Extra Virgin); Both sides very dark, Flex is only slightly better than C1, Smell of cooking oil is stronger, No sign of rot or fungus

6. '3 in 1' oil (benzine); Both sides very dark, slightly lighter on reverse side, Flex is much stiffer than C1, Slight noticeable smell of '3 in 1' oil, No sign of rot or fungus

7. Vaseline; Colour is almost back to the same as C1, Flex is stiffer, No smell, No sign of rot or fungus

 

Set #2 were hung outside on a wood frame. They got light and heavy rain with periods of sunshine,  warm overcast and wind, both light breezes and strong winds

The same oils were used in the same sequence . Control C1A was hung with the other pieces

All have been lost except;

4.  NFO Compound;  Both sides are medium dark, Flex is better than C1A, No smell, No sign of rot or fungus

In conclusion; So far there has been no rot, no fungus and most importantly NONE of the oils or fats, especially the cooking oils/fats, have gone rancid

When I have time, maybe next week, I'll start a new batch for hanging outside 

Edited February 12 by fredk

[SUP]

Nice! 

I have to make a couple of new ones too.

[YanaG]

Just wanted to say thank you for doing this experiment, information on the mineral oil is indeed very valuable!

[SUP]

1 hour ago, YanaG said:

Just wanted to say thank you for doing this experiment, information on the mineral oil is indeed very valuable!

I'm glad you found the information useful, @YanaG. Welcome into the forum.

[YanaG]

1 hour ago, SUP said:

I'm glad you found the information useful, @YanaG. Welcome into the forum.

Thank you) A lot, if not most of leather treatments sold in my country are mineral oil based, I doubt you could even get pure neatsfoot oil at all, so the topic is very helpful!

[SUP]

2 hours ago, YanaG said:

A lot, if not most of leather treatments sold in my country are mineral oil based,

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

[fredk]

On 2/12/2025 at 2:13 AM, fredk said:

. . .

Set #2 were hung outside on a wood frame. They got light and heavy rain with periods of sunshine,  warm overcast and wind, both light breezes and strong winds

The same oils were used in the same sequence . Control C1A was hung with the other pieces

All have been lost except;

4.  NFO Compound;  Both sides are medium dark, Flex is better than C1A, No smell, No sign of rot or fungus

. . .

I've found set #2. They were in a box inside the car

I'll get them sorted out, re-oiled and re-hung outside asap

I'm thinking of ending this on the 2 year anniversary. Other than darkening and some change in the leather temper nothing is happening. No rot, or nuffin. If it hasn't happened in 2 years I doubt it'll happen in 3, or 4 . . . . 

[SUP]

I'm glad you found  the set.

I've added my missing control piece.

At this point, after Sept 2025, I plan to report once a year or so. A couple of hours to report once a year I think I can do.

It appears, does it not, all in all, that leather in general is pretty forgiving of whichever oil we use, as long a we do use some oil to lubricate it? I like the mineral oil because there is absolutely no chance of rancidity no matter how much one uses.

I realized that is significant because someone I know 'stuffed' her veg tanned leather bag (t make it 'healthy', don't ask) with first olive oil, then I know-not-what because she brought it to me stinking of rancidity. Not neetsfoot or mink or coconut because the former two do not turn rancid and smelly and the latter, I recognize the smell of rancid coconut oil and this is not it. I cannot get it clean - I actually, in desperation, washed and scrubbed  it with soap and water and hung it to dry, twice, with not the slightest effect. The leather is not damaged in spite of that rough treatment. Just a little dry to the feel but the smell remains! Not cracked or warped either.  used cold water and hung it to dry int he cold. 

Planning to use Limonene on it this week end. It is ruined anyway, she cannot use it, might as well experiment.

Keeping my fingers crossed.

[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. 😃

[SUP]

Here too, there are plenty of us not making saddles and tacks. It is just that the people consistently active on this site are hardcore leatherworkers, who work with veg-tanned leathers and make saddlery, sheaths etc. or even bags, again with veg tanned leathers.  

I for one, don't make saddles or tack or anything even remotely horsey or weapon-y, since I neither ride not have weapons. So bags, shoes, caps, sheaths and sundry items it is, for me. If you find any excellent conditioners and cleaners for chrome and oil tanned leathers, please put it up here. I love to try new things.

[SUP]

Coming back to the rancidity question and the leather bag that I treated with D-Limonene.

The section that I treated first and the one that I treated 2 days later,  now 8 and 6 days ago, are still smelling of the D-Limonene and the rancid smell has not re-appeared. I live in hope. I have not cleaned the whole bag with D-Limonene as yet because I want to preserve that for comparison. The untreated part smells clearly rancid, and then the cleaned part is a relief to sniff at!

I live in hope that it has worked.

[dikman]

Just caught up on this thread again. As Sup has said, many of the commercial treatment products contain mineral oil for the bulk of the product and then add small amounts of beeswax or similar. The mineral oil is  relatively cheap for them to use and it obviously works but adding the wax thickens it up and sounds better in their advertising! 

As for using cooked chicken fat good luck with it!! I can tell you that the chicken fat from chicken cooked on my Weber definitely goes rancid and stinks to high heaven!

[SUP]

I've been checking the rancid smelling bag. The parts cleaned with D-Limonene are dry now and do not smell rancid. It appears that  D-Limonene really helps in removing the smell of rancidity. I am cleaning the rest of the bag today and once dry, conditioning it with a water based conditioner, probably the one by Chemical Guys. I like their conditioner. 

Not started the rancidity test yet. Probably this week-end or next week.

[SUP]

I conditioned the bag with the conditioner from Chemical guys. I used that because it is not oil based. So it does not add more oil to leather that has already been over-oiled. It is conditioned now and looks a little better and smells loads better.

I would not recommend D-Limonene for all leathers which smell rancid. This is pretty sturdy veg-tanned leather and while it did get some creases as it dried after the repeated washing and God knows what else was done earlier, the D-Limonene itself did not do much damage, as far as I can see. But it is still a solvent and other leathers might not respond as well. So I would decide on  case-by-case basis.

I have found a couple of small metal boxes in which to keep the over oiled leather pieces.