What’s the difference between drying and non-drying oil, and which one suits your project? Perhaps more urgently, if you’re out of one, can’t you just swap it for the other?
This can be a confusing subject, which makes this guide to DIY-friendly finishes all the more timely and essential.
The Basics of Drying vs Non-drying Oils
Drying oils and non-drying oils are two distinct categories of plant oils with notable differences in their composition and physical properties. First things first: There’s a very clear-cut difference between these two types:
- Drying oils contain a high proportion of oleic acid and linoleic acid. These unsaturated fatty acids readily undergo a chemical process called polymerization which causes drying oils to thicken and harden once they’re exposed to oxygen, creating a tough coating that protects surfaces but doesn’t leave much room for flexibility. They essentially transform from a liquid to a solid, providing a sturdy, durable finish to whatever surface you’re applying them to.
- Non-drying oils have a lower linoleic acid and free fatty acids content and remain liquid at room temperature. It won’t harden when exposed to air, stays very close to its liquid form, and will wash off with soap and water. For that reason, they will need to be reapplied and are really more of a treatment than a long-lasting finish.
There are also semi-drying oils that partially harden, but while a semi-drying oil may seem like a good compromise, don’t be fooled. Semi-drying oils give off an unpleasant smell that seems to linger, and they feel like they stay sticky long after you’ve wrapped up your project. That makes for a potentially messy finish and an unpleasant feel if you plan on touching the surface anytime soon. Imagine using corn, cottonseed, sesame or grapeseed oil as a woodworking finish and you’ll get an idea of how a semi-drying oil would perform.
Drying Oils: Examples and Use
Quite a few popular drying oils fall into this category, including:
- Linseed oil
- Stand oil (thickened version of linseed oil)
- Tung oil
- Poppyseed oil
- Perilla oil
- Walnut oil
These finishes are more likely to be refined, which involves removing impurities and other compounds that could cause discoloration such as yellowing.
Drying oils have a huge fatty acid content and need air to kick-start the oxidation process. Oxidation also produces heat; if you’re using this type of oil, you’ll need to be careful to store it properly and dispose of saturated materials promptly and safely to prevent spontaneous combustion.
Use drying oils to safeguard high-traffic, frequently used surfaces that you don’t want to feel sticky and won’t be able to re-treat with any regularity. Wood floors, decks, cabinets, countertops and some types of furniture may all benefit from a high-quality drying oil.
Non-drying Oils: Examples and Use
As for non-drying oils, these include:
- Almond oil
- Babassu oil
- Baobab oil
- Cocoa butter
- Coconut oil
- Macadamia oil
- Nahar seed oil
- Mineral oil
- Olive oil
- Peanut oil
Non-drying oils are often processed with the goal of becoming food safe. That’s ideal if you’re using them to work on kitchen counters or cutting boards and if you plan on cooking with them in between projects — after all, macadamia oil and peanut oil are downright tasty, though you might not say the same about mineral oil.
These natural oils are also safer in terms of fire risk. You can work with nondrying oils, leave the saturated rag on your workbench and not worry about spontaneous combustion turning your works in progress into a heaping pile of ash.
Non-drying oils are ideal for use in food, skincare products, sporting equipment or to condition pliable materials such as leather boots. Whereas drying oils would harden and lead to stiffness and cracking, non-drying oils keep leather buttery and supple.
Myths, Truths and Other Things You Should Know
You can use drying and non-drying oils interchangeably. (False)
Walnut and almond oil may look a lot alike in the bottle, but they’re chemically very different, which means how they react to chemical change is different too. You may be able to use them for the same purpose, but you can’t expect the same results.
One will dry faster than the other (one might not dry at all), last longer, smell better and react poorly or positively with food. Knowing the ins and outs before you choose your natural solution is vital if you care about your project’s outcome.
Linseed oil is a good go-to option. (Not necessarily)
Linseed oil has been around forever. Also known as flaxseed oil, which makes sense as it’s derived from flax, linseed comes in two forms. The first is pure, which is nondrying — it can literally take weeks to cure — and therefore impractical for many projects. That’s why someone invented a second form. Boiled linseed oil undergoes further processing, using metallic dryers to initiate oxidation and shorten the drying time.
There are a few problems with linseed oil that make it a good idea to look for an alternative.
- It’s a vegetable oil, which makes it an organic substance that’s ripe for mildew and other forms of rot.
- It won’t protect surfaces against UV light, setting you up for sun damage and weakened wood fibers susceptible to everything from fungus to insect infestations (obviously especially true if you’re using the substance for an outside application such as a patio or picnic table).
- If you don’t apply linseed oil just right — thin coats in conditions that are the right temperature — it may never dry.
- Once the solution is on and gummy, it’s very difficult to remove.
- Even boiled linseed oil that does dry isn’t hard enough to protect areas subject to heavy traffic or significant wear and tear.
It’s hard to find a finish that works and won’t hurt the environment. (Definitely not true!!)
All you want is a nontoxic oil that provides a beautiful protective finish without starting a fire or scarring your lungs in the process. Is that too much to ask? Not if you know where to look.
Real Milk Paint stocks several options, each one selected for its user-friendly, ecologically sound properties as well as its quality.
Pure Tung Oil
Pure tung oil gets right down into the wood grain and dries hard to give surfaces superior protection. It’s also safe for food prep surfaces and serving dishes — the FDA says so! — and contains no additives, heavy metals or distillates. It does take 7 to 10 days for a partial cure and up to a month to cure fully, but the results (and lack of side effects) are worth the wait.
Dark Tung Oil
Dark tung oil has all the same features as pure tung oil but with the addition of a natural resin. That resin gives the dark tung oil a deep, aged look, whereas pure tung is a light honey color.
Hemp Oil
Hemp oil is another drying oil, this time made from nutty-smelling hemp seeds. It dries beautifully to a matte finish, is food safe and lends surfaces a unique gold-green color. The intensity of the hue is dependent on seed sourcing and the solutions level of refinement.
Real Milk Paint also offers several other options that combine the best parts of individual oils to create blends tailored to more specific uses. For instance, our Outdoor Defense Oil is an outdoor wood treatment that brings together pure tung oil, pine oil and zinc and is brilliant on garden build-outs, sheds and even stone features as it protects against mold, mildew and UV rays.
Our Half and Half finish holds a blend of half pure tung oil with half Citrus Solvent to thin the product out for better penetration and absorption rates which thoroughly treat everything from raw wood to terra-cotta clay pots.
Ultimately, only you can decide which one suits the task at hand, but research and patience are key. What you don’t know could potentially hurt you, and it could most certainly derail your project. Results matter, and so does the oil you use. Select wisely and save yourself a messy, frustrating do-over.
