Medium is a vehicle that's used to thin the paint and change the drying process. Different types of mediums impart different qualities, some dry paint quicker some make it stay wet longer.
All paint has some form of medium in it already. Oil binds paint pigment together, as the pigment is just a dry powder. It's simply color and then paint manufacturers add oil to it. Most paints these days are made with either safflower oil or linseed oil. I prefer linseed oil as a medium.
So with that in mind, let’s discuss several different types of mediums and why a painter might choose to use them.
Generally speaking, paint is in it's finest condition the way it comes out of the tube. Quality paint manufacturers like Old Holland don't make a product designed to degrade with more medium. If more oil was required for the paint, they would put more oil in the paint.
So the higher the grade paint the less oil you will have in it. If you open up a tube of paint and oil spills out of it, chances are you dealing with a lower grade material. So you can you can assess the quality of paint based on the amount of oil that's in the paint because paint pigments are a lot more expensive than oil binders.
When I paint, I add extra linseed oil to the paint to thin it. This also slows down the drying process a little, but the big thing is the thinning of the paint.
The general rule of thumb when you add medium to a painting is you don't want to thin the paint unless it's your intent. You don't want to add medium to a point where the paint is no longer opaque or solid. Rather, you want a stable paint film that you can easily move about on your canvas.
This means that you never want more than 50% of your mixture to be oil. Ideally, you will have much less than half, just a little bit of oil, because the paint as it comes out of the tube is in its most pristine condition.
You should use a medium only if necessary. If you are using quality paints medium is not necessary most of the time. But if you require paint to dry quickly, slowly, or be a bit thinner, medium is a good choice.
In general, people want their paint to dry faster and for that, we use an alkyd. Alkyd is a chemical that has some solvent in it. One recognizable solvent is turpentine, which breaks down binders in the paint, drying them at a faster rate.
Alkyd will dry a painting overnight unless the paint is very thick. Generally, it will dry paintings within 24 hours that you can work layer on top of layer for several days in a row. This is beneficial for quick turnarounds in paintings and techniques like speed painting where it is necessary to paint in thin layers.
Here at Evolve, we always mix alkyd into linseed oil. And the reason is that alkyd by itself will start to dry up the paint very quickly. So if you sit down to work in a three-hour window, the paint will begin to stiffen up. While there are times this may be desirable, often mixing linseed oil into alkyd produces the most workable paint drying time.
Linseed oil is a standard and traditional medium used to make most paints. It will simply thin the paint and make it stay wet a little bit longer.
When mixed with paint it slows down the drying process so that over a long day of working your paint will remain pliable and not begin to dry or become sticky. However, it will often take longer than 24 hours to dry if used alone.
And so, I mix linseed oil into alkyd, generally in four-part linseed oil to one part alkyd ratio. And what that does is give me a medium that stays workable for several hours, but will still dry overnight. After four or so hours the paint will begin to stiffen slightly, but it is still very workable and pliable and will be dry for work the next day.
On the other end of the spectrum, if you want the paint to stay wet longer, you would use clove oil. Clove oil is not technically an artist material, it’s actually an essential oil and is available at certain markets or pharmacies. Clove oil is usually used for two things: cooking and toothaches.
However, if you take clove oil and add it to your paint it will keep your painting wet for days. Only a few drops are necessary, and you do not need to add any other medium to your paint.
When using linseed oil, it will keep the paint wet for several hours, but clove oil can extend the paint drying for four or more days with only a few drops. Again it is important to only use a small amount, and when mixed with certain colors like cadmium red, the paint will stay wet for much, much longer. These are important things to keep in mind before you use clove oil.
All in all, clove oil can be a very helpful tool for artists, particularly when working on large pieces or artists who may need to extend their palette to stay wet for several days.
Different mediums are used for different purposes. This is crucial when deciding the medium you wish to add to your paint. If your intent is to extend drying time, then consider linseed oil or clove oil. But if you wish to have your paint dry very quickly a combination of linseed oil and alkyd or pure alkyd will be helpful.
Your intent is always important to consider as you choose a medium, and keep in mind that paint in its purest form, out of the tube, is often all you need.
Note: It is important to note that alkyd and especially clove oil are not safe for animals. It is important to keep these mediums away from your pets and use in a well-ventilated room. As always, try to keep your pets out of any artist materials.
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