To Epoxy, or Not to Epoxy?

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Hey Randy,

I don’t know what “Cutting board oil” is made from, but for my cutting boards and knife handles, and also with my cork coasters, I have long had good experience with letting them soak with a drying oil and then dry, it makes it more durable and more resistant to water. I use Linseed oil and Walnut oil, and there are a few more drying oils. Linseed oil makes it darker and highlights the texture, which can look good on some woods, walnut oil doesn’t make it darker. Drying oils are available as pure oils or as drying oils which have siccatives added to it to accelerate polymerisation. With pure oil, polymerization happens, but very slowly. With drying oil variant, polymerization is happening relatively quickly.

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If you asked me this question, I would say food-grade mineral oil. It is what I have always understood to be recommended and did not think there was much dispute. After letting a few coats soak in, I finish with a coat or two of butcher block conditioner which contains more food-grade mineral oil as well as natural waxes.

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Thank you for the info! I used Howard’s Cutting Board Oil (butcher block oil), which worked well for now. I’ll look more into drying oils. I do have some boiled linseed oil, but I have yet to use it, basically because I was looking for something faster.

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I didn’t realize that epoxy continues to shrink over time. Good to know!

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Hey Matticustard,

thanks for your explanation!

The advantage of drying oils is that they polymerize, i.e. they cease to be fluid. I don’t think mineral oils do that, which I presume is why you also have to apply wax. Drying oils are oils that dry by themselves through autooxidation. The drying agents are just added to accelerate drying.

Drying oils are well-known through history as the main ingredient of oil paint (usually linseed oil, but poppyseed oil is also used). If the oil used in oil paintings would not dry, it would not be a special pleasure for the owners or museum visitors :slight_smile:

I tend to avoid mineral oils but where I use them is to protect my cast-iron planes and the machine tool tables (e.g. with Silbergleit) or to remove grease and oils (with white spirit) since here it is important that they are acid-free. However with my Japanese kitchen knifes which are made of carbon steel, I followed the instructions and have always used use pure camellia oil.

:books: Tip: :closed_book: Flexner, Bob: Understanding Wood Finishing. How to Select and Apply the Right Finish. Completely Revised and Updated Edition, 320 pages, Fox Chapel Publishing, 2010 East Petersburg PA, ISBN 978-1-56523-548-9

Edit: Seems to exist a new 3rd Edition

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This is absolutely correct. Mineral oil is a finish that requires some continual upkeep. But on the positive side, it is ready to use immediately and contains no solvents.

I’m aware that some drying oils may be able to be found in a pure state (without solvents or dryers), but don’t they take an extensive amount of time to dry? As long as they are food safe during that time and after, or you are willing to wait, then I can see why they may also make a good choice. Thank you for the information.

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I personally think using epoxy for a cutting board is a bad idea, unless the board is intended for display purposes only. Epoxy is plastic. Plastic scratches, dents and (IMO) they overall look horrible if used to actually cut things. Even the dull-ish untensils of a charcuterie board will damage epoxy inlays. Because of this, I have moved into creating inlays using wood and not epoxy (example photo: Inlay carve times? - #20 by Stefano)

Regarding the discussion of finishes, my 1.75 cents would be that for cutting or charcuterie boards, I only use mineral oil and/or beeswax. The issue with other oils or finishes is they are usually organic based and can spoil or go rancid. Also, any premade “conditioners”, “butcher block oil”, or “board butters” are nothing more than mineral oil heated to a point (crock pot) where beeswax will melt and combine. The mineral oil soaks into the wood while the beeswax provides a protective/hard coating on top. This is incredibly easy to make (and/or sell) yourself.

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Hey Forrest,

Spoiling and going rancid of a dryed drying oil? Can you cite one case where this has happened? Rancidification happens to fats and oils through oxidation, and to fats containing water through hydrolysis. But with a drying oil, the complete autooxidation is not only intended, but after drying should be nearly complete. There is no more danger of degradation through oxidation, since oxidation is already achieved.

I have never heard of this nor did I, in my 45 years of experience with using drying oils, encounter the typical odor of rancidification, neither with oil painting nor with wood finishing. Linseed oil after drying is transformed into Linoxin. The chemical reaction of polymerization cross-links the triglycerides (fat esters) together to form linoxin, which is excellent for preserving wood used outdoors, i.e. where it can get wet. Historic components, such as windows, which have been painted with linseed oil paint and maintained, can therefore be found in good condition until today. When I encountered rancidification, it was on food, which means, oils and fats that were in raw or fluid state, i.e. not polymerized.

Regarding the state of the drying oils before their use, I always have walnut oil for use in food in my refrigerator, and when it gets old regarding “best before date”, as vitamins and proteins degrade with age, I use them only for wood finishing then. Even years after expiration of best before date, I never had one that had signs of rancidification. I store them in the lowest point of the refrigerator which has nearly 0 °C.

Also it should be noted that similar to rancidification, oxidative degradation also occurs in other hydrocarbons (as found in mineral oils), such as lubricating oils, fuels, and mechanical cutting fluids.

This inlay looks really perfect. Hats off. Do you have experience with the durability of such inlays specifically when used as a cutting board? Such an inlay looks so elaborate, I would not dare to cut my vegetables on it :slight_smile:.

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Great information in this thread! I’d never heard the term “drying oils” before, though I knew what they were. Is it realistic to use a slow-drying oil finish (raw linseed oil as the easy example) for food-grade wood products we are selling, knowing the finish won’t be fully cured for several months? Or is it ‘dry enough’ after a few days to package up and ship to its final destination so the customer can immediately start prepping food?

Wood butter seems like the “easy button” route, while also allowing for another product to sell to customers for future maintenance.

I’ve offered nothing valuable to this conversation, but I appreciate the good information!

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Hey Matticustard,

yes, if you use pure oils it can take a long time, but there may be a reason to use the pure oil, namely if you want it to penetrate far into the wood before it hardens. This used to be done with wooden planes or planing workbench tops so they would never warp again. Young cabinetmakers were taught to Iay their new planes into a bath of linseed oil for a week or until it sinks[1,2]. But for this you had to take weeks, when you could not yet use the equipment.

There are two ways to use the drying oils with wood: Either I want the wood pieces to be completely impregnated with the polymerizing oil, in which case I use pure, unheated drying oil. I always collect the wooden things, such as cutting boards and cooking spoons, before I make such an action, so that it is worthwhile.

I once treated a very old spruce table top, about 1½ " thick, by applying pure linseed oil over and over until it came out on the underside. Then I let it dry for two months. This is an extreme example, but the finish is incredible, it looks like plastic, and the wood texture comes out very nicely. It’s very hard and I can put a wet bottle down without a coaster and the water just beads up.

Or I want a quick water-repellent coating: Then I use something called “Leinölfirnis” here. You get it from woodworker suppliers as well as from artist suppliers. This is heated (prepolymerized) linseed oil with siccatives added. The heating procedure makes it thicker, which means it doesn’t soak into the wood as well. Because of the siccatives, it begins to dry in a few minutes of contact with air, and after I have applied it so many times that the wood no longer absorbs anything, at the latest after half an hour, I have to wipe off the excess, otherwise it would become sticky and whitish and hinder polymerization. After complete drying (12-24 hours), this can then be repeated a few times, but only achieves a penetration depth of one to a few millimeters. Although it gives a good water repellent coating, it then remains possible that the wood inside still warps or soaks up water when left in the water. To make it penetrate deeper, you can heat it slightly beforehand to lower viscosity, or you can mix it 1:1 with natural turpentine oil or orange oil. They do not take part in polymerization, they evaporate completely.

Regarding food safety, if I look at the datasheets of e.g. linseed oil based Livos ARDVOS Holzoel Nr. 266, such products are approved for contact with food.

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No, and granted I do not have that many years of experience in this arena, but I have always used mineral oil for many years with my cutting boards, well before I started making them.

Here’s a link to a pretty decent explanation of different oils, including a modified coconut oil, and their pros/cons. What Type of Oils are Safe to Use on Your Cutting Board - CuttingBoard.com

Basically, my takeaway from this is, yes it’s possible to use a few different types of oil finishes for cutting boards, but I don’t see the need to take any risk and just stick with the inexpensive mineral oil option.

A quick segway, regarding my cast iron pots and pans, I use an organic oil like grapeseed when seasoning the cast iron, but I heat it to well over the oil’s smoke point (e.g. 500°F or more) which, in my limited knowledge, causes the oil to polymerize and bond to the metal and will remove the components of the oil (e.g. fats) that cause it to go rancid. My litmus test when seasoning cast iron is, when it stops smoking, everything that could cause rancidity has been burned off.

I don’t have any long term, real world, examples of the inlay’s durability, but my initial tests with a chef knife showed no more damage to the inlay compared to the surrounding wood. Just to note, in the example I showed, the charcuterie board is made from red oak and the inlay is .25" thick walnut. And I did another one with red oak and African black wood inlay which actually dulled my endmill after cutting it. So, I have fairly high confidence that walnut is going to hold up better than epoxy when using a sharp knife. Besides, “when” the board does get scratched or damaged from use, a light hand sanding and reapplication of mineral oil is all that “should” be needed. I just don’t see that type of restoring or “maintaining” of a board with epoxy as being reliable if at all possible.

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Hey Forrest,

I’ve looked at the site, but find little solid and no valuable source information, more of a collection of hearsay. What I find questionable is that it is said that boiled linseed oil (which in reality is never boiled, of course) contains substances that are “treated with chemicals that make it toxic for humans”, and therefore are out of the question for use in cutting boards. In fact, the siccatives added in extremely low quantities to heated linseed oil are metals such as manganese, cobalt, zirconium, calcium and zinc. Of course, I would not drink a glassful of such oil. However, it is very questionable whether any of this is given off by drying oils that have dried (polymerized). Due to the polymerization of the drying oils, they are no longer soluble, neither in oil nor in water (unlike non-drying or mineral oils). For example, the above-mentioned Ardvos Wood Oil No. 266 contains manganese, zirconium and calcium as siccatives, but is explicitly approved for contact with food and for use in cutting boards.

In addition, the page you linked says: “Unfortunately, all fats exposed to air eventually go rancid”.

All fats? In reality, however, in the case of drying oils (which do not actually dry, but polymerize), the very oxidation, i.e., contact with air, that would otherwise cause spoilage is used to polymerize these molecules so that they are no longer available for the oxidation processes that cause spoilage.

This is also what I find deficient about the above page: it does not point out the difference between polymerizing and non-polymerizing oils. However, the transformation of liquid oil into a polymer by auto-oxidation is the crucial property for the longevity and for the non-occurrence of rancidity, which the non-polymerizing vegetable oils and the mineral oils lack: they always remain liquid, and the glycerides, which are not linked, are open to oxidation, i.e. to degradation or building chemical compounds that smell bad. That’s why I’m not surprised that they report foul odors with coconut oil.

Of course, with all oils, you can try to remove as many degradation-prone components as possible by refining and distilling, in order to try to prevent spoiling and rancing, but they won’t become a polymerizing oil by doing so.

I, being a curious person, long ago just dumped some linseed oil into a saucer and left it on the windowsill for many months. The linseed oil slowly turned into an elastic mass that at no time showed any bad smell or other negative change. Not even after years (I think I still should have that saucer of linseed oil somewhere). The only thing that has accumulated is dust :slight_smile:

By the way, linseed oil is not only the main component of oil paint, but also of traditional putty and of linoleum.

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There is a lot of interesting scientific information being brought up . However, I wonder if there are some less scientific factors that also deserve consideration — e.g., the sniff test.

Mineral oil has the benefit of being colorless and odorless. It won’t impart any of its own essences onto your food.

Linseed oil may be odorless when fully dry, but I’m not personally willing to wait weeks or months for that to happen. And while I realize it may be a personal preference, I do not find the odor particularly desirable.

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Hey Matticustard,

I’m sitting in a room with many homemade bookshelves treated with quick-drying linseed oil varnish. They smell of nothing.

It is applied within minutes, approx. for about half an hour when it begins to harden, and is dry after 12 hours and can then be overcoated with a second coat.

For the interior of cabinets and drawers, I would not recommend linseed oil, since there is insufficient oxygen and light supply, but shellac instead (alcohol-based).

I mainly use the pure, slow-hardening linseed oil when I want to make something water-resistant down to its depths, i.e. when I want it to be completely soaked with it, e.g. cutting boards in the kitchen, or workbench tabletops that I don’t want to warp in the future. For furniture, I rather use quick-drying linseed oil when I like the darkened color of the texture, but more often shellac because it dries extremely quickly and does not darken the color of the wood.

The kitchen accessories I treated smell of nothing too. It’s really just when applying that it smells of linseed oil.

My opinion about linseed oil and other finishing materials comes from many years and various use. I would say that you can not judge it only from theory, you should own and use a few items that you have treated with it to judge it. Also the book mentioned above contains a lot of information.

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Hi,

Being a novice in this field I won t advise about the spécifications and benefits of it, simply to feedback that I used fractionnated coconut oil for my cutting boards, and I m quite happy with it.

My préférence is based on the point its organic and not from oil, It s not smelling, stable and dry fast.

I ll compare once with linseed oil, I ve heard it s a good option as well.

Cheers
Stefano

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Well, I really had to slow down and reread a ton. I do believe I should have some sort of certificate after processing all of this :grinning:. You are all awesome, and I appreciate all this info!

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Hey, @LostInTheGarage , one thing that I’m surprised no one brought up while discussing epoxy on a cutting board is that the whole point of a WOODEN cutting board is that it not only is easier on your knives but also is much better at defeating bacteria than plastic ( or epoxy). This is because most cuts in wood ‘heal’ or close up whereas plastic slices and leaves narrow valleys, a perfect home for bacteria. As far as goes finishes, I used to fret about food safe products until I realised that once dry, almost any finish is inert, food safe and and fit for purpose.

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Hey Charles,

more than that, wood seems to have antiseptic properties.

Aviat et al.: Microbial Safety of Wood in Contact with Food: A Review
Comprehensive Reviews in Food Science and Food Safety
Volume 15, Issue 3 First published: 26 February 2016
https://doi.org/10.1111/1541-4337.12199

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I agree 100% with Matt and would never use epoxy on a cutting board, and he is also right about problems with wood, aging etc., however:

IMG_2329
IMG_23291920×1056 255 KB

on (rare) occasions CNC efforts, wood and epoxy look pretty good.

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That looks really cool!