Natural Leather Finishes

[Martyn]

3 hours ago, spectre6000 said:

(hint: I disagree with Martyn on chemical and historical grounds).

Hey, I'm quite happy to be wrong.

But I am trying to learn too, so some explanation of why I'm wrong would be nice.

Edited June 6, 2016 by Martyn

[spectre6000]

Sure. It's all laid out in the Chemistry thread, but here's the short take:

Historical: Linseed oil (aka flax oil) is what was used to make patent leather back before it was plastic garbage. Boiled (to accelerate breakdown of the triglyceride into the polymerizing free fatty acids) and combined with carbon black and Prussian blue (pigments), it was applied in many coats over many days, then polished to a high shine resulting in a "black, flexible, and durable leather with a high sheen". 

Chemical: Linoleic acid is just the name for a fatty acid (not an acid in the battery acid/Batman's Joker/Wicked Witch of the West sense, just that the pH is <7) with a specific number of carbon atoms (18 in this case) and two double bonds. These fatty acids are arranged on a glycerine backbone called a triglyceride (oil in this case). The two double bonds are places on the molecule that are susceptible to bonding preferably with oxygen. When they bond with oxygen, the molecule breaks apart into (a diglyceride and) a free fatty acid. This breaking/bonding with oxygen is what is commonly called 'going rancid', but 'rancid' in the common sense typically refers to a specific smell; that smell is a particular aromatic compound or group of compoinds. In the case of linseed/flax oil though, the byproduct of this reaction is a free fatty acid that dries and polymerizes into a plastic like substance that is flexible and durable (see historical reference).

Coincidentally, the primary fatty acid present in neat/neetsfoot oil is oleic acid, which has the same number of carbon bonds, but one fewer double bond. Since it only has one (and the location of it), it's less likely to decompose and the byproduct is different. I'm pretty sure it's an aromatic compound that actually smells 'rancid'. 

All (non-petroleum) oils are just naturally occurring combinations of triglycerides with varying numbers of carbon bonds and varying numbers of double bonds in various locations and orientations. They all break down, or go rancid (neat/neetsfoot oil is not magical in this way). The byproducts of decomposition can smell bad ('rancid'), smell good (leather, vanilla, spice, etc.), or not smell at all (polymer).

In my own experiments in treating vegetable tanned leathers with various oils and combinations of oils in various percentages, stages, etc. my findings from linseed/flax oil are summarized as follows:

- Initial smell is probably the best leather smell. It smells characteristically of leather, but sweet. Very pleasant. This is the only oil save walnut (a hint of earthy spiciness) that has any notes on smell. The smell dissipates after a day or two and is no longer distinguishable.

- Color is average.

- Flexibility is average.

- Dispersion is average. I applied the oil to one half of the sample  (demarcated with painters tape), and observed natural distribution over time.

- Sheen is average initially, but seems to be increasing with time. Same with walnut (similar fatty acid composition). Where the oil has been applied is slightly shinier than where it hasn't. This effect should increase over time and with additional applications. 

Methodology: I took several 3"X4" scraps of vegetable tanned leather and applied various oils as usual to one half of the sample. Add time and observe. See the chemistry thread for photos, and lots of extra detail.

Edited June 6, 2016 by spectre6000

[Martyn]

Thanks, that is very helpful.

Re linseed oil, did you use boiled or raw? I was reading about one chap who was trying to make oilcloth with raw linseed alone and he said it took a couple of months for the oil to oxidise/polymerise fully. What kind of time frame did your experiments cover?

Your photos dont show up for me in your chemistry thread BTW.

[spectre6000]

Raw. I'm not expressly after the polymer finish. I'm hoping to see it be one of those things that improves over time and with use and upkeep. See time stamps for approximate times. Aside from suggesting you use Chrome, I don't know what's up with the pictures. I posted them shortly after the forum switched to the new format, and made sure at the time they were displaying properly in Chrome, Firefox, and Safari (please never ever use IE -the internet). Now, however, I'm only seeing them in Chrome. It's been too long to go back and edit them, so I really don't know what to tell you... That's really annoying... I put a lot of work into that.

Outside of the raw oil testing, it's being used in conjunction with a blend of oils and waxes that I'm working with in an attempt to create an especially spectacular oil finishing system. Results so far have been better than anticipated. All that research and experimentation gave me a tremendous amount of insight into the roles the oils play in leather modification and preservation, and the effects they have on color, flexibility, smell, feel, etc. What's the most interesting is the analysis of the byproducts of oil decomposition in leather, and the associated effects on the same. Time is still a factor I have yet to be able to account for fully due to lack of said time machine, but based on historical uses and analysis I am more than confident in the long term viability. The question is simply one of how much better things will get!

[Martyn]

It's very interesting. I was hesitant to use untested formulas on my backpack as the stitching is 70 years old as well as the leather and canvas. I think you've inspired me to make a few of my own test swatches with different recipes. I'm surprised you haven't seen some loss of pliability with linseed though. It's hard to imagine something that oxidises into a plastic-like polymer doesn't change the feel of the leather.

I dont use IE, I used Netscape Navigator back in the day and firefox for the last x years. I also never put pictures into a forum database. I host them externally in photobucket for exactly this reason.

Edited June 6, 2016 by Martyn

[spectre6000]

I'm hosting these from Google Photos. I got really fed up with Photobucket a few years back right around the time Google came out with the photos service. I'm a software engineer by day, and Google's offerings are generally very highly regarded. So far, I've not been disappointed. 

One of the biggest takeaways from my research in the broadest sense was that there really isn't a bad oil. There are pros and cons to pretty much all of them, and neetsfoot oil is not special in any way save mythology and lore. Actually, I take that back. It smells like crap. It's pretty special in that regard... Olive oil is very close in terms of lipid composition, and it smells nice and I don't mind if I get it on (anything). 

Actually, one of the reasons I'm thinking neetsfoot oil might be so common is that when petroleum oils displaced it as machine lubricant, light colors were in vogue (B/W TV showed that cream color pretty well). These days, it seems the rich dark mahogany-esque colors are more desirable, and in that regard, neetsfoot is not very good at all. Rapeseed (canola) oil, and an oil wax blend have had the best results for darker colors so far. It's all in how they interact with light when combined with the leather fibers. 

[CraftyNick]

Hey everyone!  Sorry I've been a bit out-of-the-loop on this thread.  Some of it is a little over my head on the chemistry side of things   but the information and shared experience has been great.  It sounds like it is an acceptable practice to experiment with natural oils.  Linseed oil is a good one to work with.  Let me know if you come up with any other good thoughts!

[spectre6000]

Do your homework. Be aware that linseed oil is often BOILED linseed oil, and almost as often adulterated with crap you probably don't want in your leather. Boiled linseed oil is what was traditionally used for making patent leather, but make sure you're not getting boiled linseed oil and various flavors of dinosaur squeezings. Flaxseed oil is what I used. You should be able to find it at any quality grocery store in the specialty oils section (or strangely in the refrigerator of the "juju" section at Whole Foods).

[Martyn]

6 hours ago, spectre6000 said:

Flaxseed oil is what I used.

Food grade linseed oil will still polymerise, it's just going to take months rather than days or weeks. If you really want control over the mix, you can get all sorts of high grade linseed oild from Windsor & Newton...

You can get refined linseed oil, linseed stand oil, drying linseed oil, cold pressed linseed oil, thickened linseed oil etc...

You can also get various qualities of boiled linseed oil, some have additives to speed drying, some dont. Liberon BLO for example, has just had air passed through it to accelerate drying times. Others like the W&N thickened linseed oil have been super heated for the same purpose.

Edited June 14, 2016 by Martyn

[spectre6000]

That's some research! Polymerization isn't bad though. Nor is the amount of time it takes to polymerize. If you WANT the polymerization, and you want it quickly, there are ways to break the triglycerides down faster. The classic example is boiling, which uses energy from heat to break the molecules apart quickly. If you use the food grade stuff, you're relying almost exclusively on time.

For my purposes and intents, this latter scenario was desirable; my philosophical view of leather is that it's a natural material with excellent wear properties that gets better with time and use. The polymerized film at the surface (combine with waxes, etc.) will, in theory (in test), add to the beauty of an item over time. He mentioned in the video that it's an elastic consistency when it cures (this is the polymerized result), and on/in the surface of the leather this seems like a very positive result. It'll protect while adding shine, depth, and color (darkening somewhat). If you're going for a patent leather type finish though, this would definitely not be the way to go.