Thinning oil paint is an inevitable part of using it. You’ll almost always need to, to make it manageable, achieve particular effects, and most importantly, avoid breaking the rules of oil painting.
Therefore, many newbie oil paint artists often ask, what can I mix with oil paints to make it thinner? You can mix solvents, oils, or mediums with oil paints to make it thinner. Each method has its own pros and cons to consider.
Your choice of thinner will rely on various factors, which we shall cover in this post. Keep reading to learn more about how to thin oil paints and the best thinners to use.
Why Thin Oil Paint?
Oil paint is thinned to improve its flow or viscosity. Different techniques such as layering, glazing, impasto, and Plein painting require the oil paint to have a certain level of viscosity which is arrived at by thinning.
From a professional perspective, thinning is not debatable if you go by the rules of oil painting. And these rules determine the type of thinner to use at various stages of painting.
When layering, for example, fat over lean is the standard recommendation. This essentially means lean layers sit at the bottom and fat layers at the top.
Thin layers are made by mixing the oil paints with solvents hence are solvent dense. Fat layers mean the oil paint is oil dense either by being mixed with fewer solvents or with oil thinners.
Another rule is thick over thin, which again suggests that the bottom layers be thinner than top layers to prevent sinking in and cracking during drying.
For a more visual explanation about the fat over lean rule, here’s a great video from Windsor & Newton on YouTube.
It is not the painting techniques and rules alone that determine the thinner you should go for. Toxicity levels, environmental impact, and even your budget can also influence the type of thinner you choose.
The Best Thinners For Oil Paints
Let’s go over the different types of thinners available for oil paints.
There is a range of products you can use to thin oil paints. These can be broadly categorized into three types; solvents, oils, and mediums.
The different thinners under each category have varying effects on the oil paints. This is regarding the consistency, drying time, and appearance of the finish.
Therefore, you have to choose your oil paint thinner carefully to get the desired and long-lasting results. Let’s explore them one by one.
Solvents
Solvents are the most recognized oil paint thinners under the sun, and every oil paint artist is familiar with them. They are chemical-based, characterized by a runny consistency and strong chemical odor due to the presence of VOCs.
The greatest advantage of solvents is that they work rapidly and mix exceptionally well with oil paints. They are also very effective as thinners; hence you must use them a little at a time.
Depending on the amount you use, your oil paints can be anything from the consistency of cake batter to as thin as milk. The more you mix into the paint, the lighter it becomes.
Solvent thinners also alter the appearance of the finish of oil paints. Oil paints usually have a glossy sheen when dry, but solvent thinners transform the finish into matte.
You may consider solvents as thinners if you don’t have too much to spend since they are very cost-effective. They are the cheapest oil paint thinners you can find.
It is the nature of solvents to evaporate pretty fast. Therefore, the paint dries through evaporation, which is a quicker process. Adding solvent thinners into oil paint significantly improves their drying rate from slow to moderate.
Solvents are suitable for layering. You can incorporate it in your bottom layers as per the slow drying over fast drying and thick over lean rules.
They are, however, not a good choice of oil paint thinners for glazing techniques. Glazing requires more oil in the paints, and adding solvents to your oil paint cuts back more oil.
The biggest downside of solvents is perhaps their toxicity. Solvents dissipate into the air in the form of toxic fumes.
The smell is so strong it is not even tolerable by sensitive people. These fumes are dangerous to human health if inhaled and are generally not good for the environment.
If you still choose to use these solvents, you must work in the open air space or where the ventilation is very good.
Under the solvents category are the following thinners:
Turpentine
Turpentine is the one thinner that the majority of people are familiar with, even those without vast art knowledge. It is almost like general knowledge.
Well, turpentine is the oldest thinner to exist, which explains its popularity. It is a product of pine tree resin extracts and evaporates quickly with intense fumes.
Turpentine thinned oil paints will dry at moderate speed and produce a matte finish. It is ubiquitous, cheap, and the most preferred oil thinner despite its carcinogenic profile.
Mineral Spirits
Mineral spirits function similarly to turpentine, except that they don’t evaporate as fast when exposed to air. The thinner is derived from petroleum distillates which are chemical by-products of petroleum.
Mineral spirits have equally intense fumes, but you can find something a bit softer if you go for artist-grade versions rather than those in hardwares.
Like turpentine, mineral spirits have a low viscosity and improve the drying speed of oil paints to moderate. They also result in a matte finish.
Gamsol is a fantastic example of an artist-grade mineral spirit used by oil painters. Most of the harmful aromatic hydrocarbons in ordinary mineral spirits have been removed, making it a “healthier” choice.
Oil Of Spike Lavender
Oil of spike lavender is the only plant-based organic solvent hence non-toxic. It has a welcoming smell too, thus a pleasure to use. You don’t have to worry about toxic inhalations.
It dries much more slowly though, compared to the other mentioned solvents. The end result is a satin finish with a bit of sheen compared to matte finishes of solvent thinned oil paint.
This solvent is highly effective and thus highly priced too and hard to find. However, you need to use just a tiny amount as it is a more powerful thinner than turpentine.
How To Thin Oil Paint Using Solvents
Solvents evaporate quickly and get contaminated very easily too. Therefore you must use a little at a time.
For fine artwork:
- Wear appropriate safety gear such as gloves and respirator and ensure you are in a well ventilated space.
- Squeeze some paint onto your palette.
- Pour a small amount of solvent into a container preferably with a tight lid.
- Dip a clean paint brush in it. You can immerse it halfway through the bristles, less than half, or completely depending on the consistency you want.
- Using the wet brush mix the paint on your palette.
- Use a clean brush every time you dip for more solvents. Otherwise, have a separate solvent bath to clean your brushes.
Alternatively:
- Put a dollop of paint on your palette, then using a dropper, suck up and release a few drops of solvent on the paint.
- Mix with a brush or palette knife. Add more drops of solvent to adjust accordingly.
For large batches:
- Transfer a good amount of paint from the can into another container.
- Pour the solvent directly into the oil paint and stir. It should be half the amount of paint (2:1).
- Adjust if necessary by pouring in more solvent in small amounts to thin it down further.
Types Of Oil Thinners
Adding oils to your oil paints is another way to dilute them. The explanation is straightforward since oil paints have oil as part of their constitution.
But unlike solvents which are low viscosity thinners, oil thinners are medium viscosity. Furthermore, they are slow-drying. Oils dry by curing, unlike solvents that dry through evaporation. Curing is a time-intensive process hence the slow drying time.
On the bright side, many artists who prefer a less harsh and eco-friendly thinner use oils. They are pure and do not give off choking smells or toxic fumes.
If you were to go with the slow drying over fast drying and fat over lean rules, you’d use oils to thin your top paint layers. You can also thin the bottom layers with oil if you do not prefer using solvents. But then mix twice as much thinner for the subsequent coatings.
Oil thinners are amazing for glazing techniques and leave the surface glossed up. But before reaching out for your olive oil or other vegetable oils in your cabinet, note that not any kind of oil works when it comes to thinning oil paints.
Vegetable oils are non-drying oils. Mixed into oil paint, it will never dry. Only drying oils are used to thin oil paint, and still not all. Here are a few select oils.
Linseed Oil
Linseed oil is part of the ingredients of many oil paints, making it the most compatible oil thinner. It is also widely used in oil painting for other functions.
The centuries-old plant-based oil is extracted from flax seeds and is loved most for its stability. Its drying time is rated as moderate to slow. It creates a dry superficial layer first, even though the bottom of the paint is still wet.
Where linseed oil loses points is that it yellows badly with time. Therefore, if it is used to thin light colors such as white, cream, or other lighter shades, they will show signs of yellowing in the future.
Fortunately, this does not happen immediately and can take a couple of years to notice.
Walnut Oil
In a contest, walnut oil will take second place as the people’s favorite oil thinner after linseed oil. The plant-based oil is extracted from walnuts and was discovered ages ago.
It is much slower drying than linseed oil, yet manufacturers prefer it in paint production. This is because oil paint made or thinned with walnut oil does not yellow or crack.
It makes really long-lasting paint coats when used to thin oil paints and, in addition, enhances the vividness of colors.
Safflower Oil
Another type of oil that you can use to thin oil paint is safflower oil. This is the slowest drying among all oil thinners.
What happens with safflower oil is that it dries evenly as opposed to other oils that form a dry top layer first. The paint remains sticky throughout the drying period, which is not a very desirable trait considering dust and accidental smudging.
It has other good qualities, though. For example, it doesn’t yellow as badly as linseed oil, and it is relatively stable.
Poppy Oil
Poppy oil can be used as a thinner but with some reservations. To begin with, this oil is not very stable, so you wouldn’t want to use it in your entire painting.
If it is the only oil you have, it can be beneficial as a thinner for the initial layers. The drying time is prolonged as well.
Stand Oil
Last but definitely not least is stand oil. Stand oil is polymerized linseed oil. In other words, it is linseed oil that has been heated in the absence of oxygen.
This process rids the oil of impurities that cause oxidation and thus yellowing in ordinary linseed oil. It also thickens the oil making it highly dense than any other oil thinner here. Stand oil dries much faster than linseed oil though the rate is still considered moderate to slow.
The oil is one of the purest, and higher forms of linseed oil yet remains unpopular compared to regular linseed oil as a thinner. It is expensive too.
How To Thin Oil Paint Using Oil
Thinning oil paints with oil is more or less the same as with solvents. You can blend the oil and paint in the palette using a brush or pour it directly into the paint.
You must maintain the same standards of purity. You can avoid cross-contamination by using a little oil at a time, changing it when it appears dirty.
Because oil doesn’t evaporate, you can take your time and do not need a lid for the container holding the oil. You don’t need safety gear as well.
Oil Paint Thinning Mediums
The third class of what you can use to thin oil paints is mediums. If you’ve been painting long enough, you know that this name is given to manufactured liquid products meant to be added into paint to make it work better.
Medium thinners are certainly better than solvents and oil thinners in some aspects. They are high-viscosity yet the fastest drying thinners compared to oils and solvents.
Mediums are synthesized from a blend of solvents and products of distilled petroleum.
Unfortunately, this makeup is chemical-based, and they emit fumes with some degree of toxicity. The smell is, however, more tolerable than turpentine.
Oil paint thinning mediums are loved for their effectiveness and consistency. Also, they enhance brilliance and gloss.
There are many art supplies brands, each trying to outdo another by making their own versions of thinning mediums. We can’t exhaust all of them in one post. So we handpicked a few remarkable medium thinners for oil paints.
Galkyd
See recommended product on Amazon.
Galkyd is a medium for thinning oil paints made by Gambling. If you’ve used other Gambling products before, then you are aware of their quality standards and effectiveness.
It is a highly viscous thinner with excellent blend-ability. It improves consistency, dries fast, and maintains the high shine of oil paints.
Other versions of it are designed to be slow drying and have a low gloss finish, namely Slow Dry and Lite.
Liquin
See recommended product on Amazon.
Liquin has also received massive recognition and admiration from artists of all skill levels. It is also a petroleum distillate formulation by Winsor and Newton and works in the same manner as Galkyd.
How To Thin Oil Paint Using Mediums
To thin oil paints with a medium, follow the manufacturer’s instructions for usage. The steps are, however, just about the same as other thinners.
There you have it, the different ways to thin oil paints. Hopefully, you can explore a few of these to find what works for you.
To give you a head-start, here is a summary of the oil paint thinners. If you want a highly effective option with a thin consistency, and a low price, go with solvents. If you prioritize health and safety and a slow drying process, go with oils.
To find both effectiveness and fast drying properties, go with mediums. Happy painting!
Up Next: The Best Varnish For Oil Painting