Using Mediums With Oil Paints

You always hear about adding mediums to your oil paint, but what the heck does that mean? We’ll go through it in this lesson so you won’t be intimidated by that giant wall of mediums next time you go to the art store.

Here are the topics we’ll be discussing:

Rule #1: Fat Over Lean

Rule #2: Thick Over Thin

Uses For Mediums

How Do I Start?

Exercise 1: Experiment With Different Techniques

Mediums can be used for a wide variety of purposes, and one of the main reasons to use it is to give your paint a little bit of gloss. Mediums also help your paint flow better and can be essential in blending and adding depth.

Before getting into a discussion of “fat” and “lean”, let’s look at some rules when painting with oils:

Rule #1: Fat Over Lean

When oil painting in layers, each successive layer must be more flexible than the one underneath. This rule is maintained by adding more medium to each successive layer.

Explanation: Fat is the amount of oil you add to your paint and lean is the amount of thinner, solvent, or turpentine you add. The more oil in the medium, the fatter it is. Think about eating dinner—salad first, then the good (i.e. fatty) dessert at the end. The salad—the starter—is lean, meaning your paint will first have more thinner or solvent in it. The fat, which we use in the upper layers, has more oil. By the way, you won’t just use these mediums straight out of the container—you’ll mix them to come up with your own combination that works for you. We discuss this below. For more about painting in layers, see our Glazing in Oils lesson too.

Rule #2: Thick Over Thin

Explanation: Thick layers of oil color are best applied over thin under layers. Thin layers on impasto paintings are likely to crack.



Solvents are used to thin your paint and clean your brushes.

This will be your leanest medium you use. Mix a little of your turpentine or Gamsol into your paint to thin it out for the first layer. This will help it dry quickly so you can start painting straight away, instead of waiting for it to dry before you move on.

If you look online or read books about oil painting techniques, a lot will give you recipes for mediums that use turpentine. Turpentine used to be used because it was the only option, but in the 20th century, odorless mineral spirits (OMS) were invented, providing a safer alternative to traditional turpentine. Gamblin makes a product called Gamsol which is one of the best OMS on the market. It’s made with the knowledge hat it will come in contact with your body, so most of the bad stuff has been removed. It doesn’t smell and it has a high enough flash point that it can be shipped via airplane as a non-hazardous material.  It’s better for you in the long run. It’s more expensive than, say, paint thinner from the hardware store, but your health and safety is worth it. Trust me.

Pro Tip: If you try to pour Gamsol into your solvent container the way that seems most logical (with the spout side down) it will spill everywhere. Pour it like this:

Screen Shot 2016-07-18 at 9.59.40 AM

  …and it won’t spill.



Mediums are fatty additives you add to your paint.  There are thousands of different kinds you could use, but we suggest just using a simple alkyd medium. Gamblin makes Galkyd and Winsor & Newton makes Liquin—both are very easy to use and there’s no need to worry about cracking. Traditional mediums are sometimes made from toxic materials—they can crack, turn dark or yellow with age, and on top of all that, you have to remember precisely how much solvent or oil was in the last layer you painted so that you don’t add a lean layer on top of a fat layer. It’s a lot to think about, which is why we are streamlining the process and only using one alkyd medium.

For more in-depth information on mediums, see the appendices to this lesson in the Student Resource Center. Appendix A talks about solvents, Appendix B has info on oils, alkyds, and other additives, and Appendix C goes over some varnishes. If you’re interested in mediums beyond what I discuss there, then do your own research. Honestly, I think it’s part of the fun. The more you learn, the more options you have. It’s like Degas said, “Painting is easy when you don’t know how, but very difficult when you do.”

Uses For Mediums

Not only do mediums improve the flow of paints, they can help you achieve the look you want for your painting. Here are a few common techniques:


Glazing: Glazing is the build up of layers of transparent or semi transparent color over dry underlayers. It is a lengthy technique where the effects in oil are unmatched when compared to other media. There are a lot of different mediums you can use in glazing.


Scumbling: Loosely brush a thin film of opaque or semi-opaque color over your underpainting. This may actually show through in places and can retain an important influence on the surface appearance of the painting.


Impasto: This is the technique of applying paint thickly, so that the brush strokes are plainly visible and create a textured effect.


Stipple: A bristle brush and thick viscous color can create a “stipple” texture. 


S’graffito: “S’graffito,” the technique of scratching into a wet oil film, can be done with the pointed end of a brush, painting knife or any scraping device. It is effective in defining outlines or details for expressive effects.

How Do I Start?

Begin with your underpainting. Underpainting can be done in monochrome using any just about color, or it can be done in full color if using fast drying colors. Because it is the first layer, it should be your thinnest layer of paint. Mix your paint down with solvent until it is very runny and resembles watercolor.  After your underpainting is completed, you can begin adding alkyd medium to your paint.

Remember, you only need a small amount of medium. You want your paint to glide smoothly on the canvas. If it is too thick and difficult to move, add a little medium. If it’s too runny or clear (not enough pigment), you’re using too much medium—add more paint.

They attach to your palette with a little built-on clip. Both have lids so I can save my medium until my next painting session.

palette cups on palette

You’ll put your alkyd medium in one palette cup and clip the cups onto the side of your palette. When you start painting, pick up a little medium on your brush and add it to the paint or paint mixture you’re going to use. A good rule of thumb is to use less than 25% of medium to the amount of paint. You need very little medium.

Exercise One: Experiment With Different Techniques

Get a blank canvas or piece of board at least 6” x 6” and start playing with your solvent and medium. Try some of the techniques listed above—which combination works best when you try to scumble your paint? Or scratch some s’graffito into it?

One Response
  1. March 19, 2018

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