Mediums and Solvents
Mediums
Synthetic Mediums
Oil Painting mediums can be classified into two types: natural and synthetic. Synthetic mediums, such as Liquin and alkyds will always produce a synthetic, ‘plasticy’ look to your finished painting. They will speed drying time and add body to your paint, but their additives often have a strong odor. Liquin, for example, is made from Petroleum and smells similar to Kerosene. If you choose to use synthetic mediums, avoid mixing them with natural mediums—odd reactions can happen such as gooping, clumping, and crumbling.
Natural Mediums
Natural Mediums are safer, more intuitive to use, more traditional, and your finished work isn’t ‘plasticy’.
In order to understand how and when to use mediums, we have to understand the Fat-over-Lean principle. This allows you to make informed decisions.
Fat-over-Lean Principle
Oil paint doesn’t dry—this implies evaporation. Oil paint hardens. This occurs through a chemical reaction called polymerization, where oxygen molecules penetrate the oil matrix and bind Fatty-Acid chains together, solidifying the medium. It is the hardening of the oil through polymerization which ‘dries’ oil paint. So, a paint with more oil content in it hardens slower. Fat-over-Lean doesn’t refer to paint thickness. ‘Fat’ refers to oil content. ‘Lean’ refers to less oil content. For example, if you mix a solvent into an oil paint, you’ve made it leaner, and the oil content will harden quicker. The phrase ‘Fat-over-Lean’ means that layers of your oil painting don’t need to become thicker, but need to have more and more oil content, or become ‘fatter’. If you put a ‘lean’ layer over a ‘fat’ layer, the top layer hardens quicker than the underlying layer and when the oil in the underlying layer eventually solidifies, the top layer cracks. You’ll see these cracks in very old oil paintings, made in the first years of oil painting when this principle wasn’t understood.
What Oil Painting Mediums do:
Effect | Property | Effect |
|
|
|
Make it leaner
Make it ‘dry’ faster
Make it more fluid
Make it matte
| oil content (oils)
drying time (driers)
consistency (oil/impasto)
luster (varnish)
| Make it fatter
Make it ‘dry’ slower
Give it more body
Make it glossy
|
Driers
There are a variety of ‘driers’ sold in art supply stores, but they are usually very toxic. Avoid them. The most common is Cobalt Drier, which has pure cobalt in it. The best way to speed up ‘drying’ time, is to alter the oil content of your paint. Add a solvent to make it ‘leaner’ and that layer will harden quicker. This should only be done in early layers to follow the fat-over-lean rule. Middle and final layers of your painting should have more oil content, but these layers should also be taken slowly and with consideration. Oil painting requires timing and patience. I am choosing not to give information on driers, because I strongly believe they should be avoided. If you absolutely need a layer to dry a bit more quickly, add a thicker-bodied oil.
Thinners/Solvents
There are so many different solvents and thinners found in art supply and hardware stores. Many of these are harmful to you if they contact your skin, are ingested, or if the fumes are inhaled. Many thinners and solvents are labeled ‘odorless’, even in art supply stores in the oil painting section. These are not odorless! They have a very strong odor, and after a short use indoors you will feel the effects—headache, nausea, or worse. There are ‘natural’ solvents such as Turpentine (pine sap distillate) and Grumtine (citrus peel distillate). These smell great, but the fumes are very harmful. The most natural solvent is Lavender Spike Oil, steam-distilled from Lavender plants. If it is pure (no solvent additives) it is the least harmful of all solvents, but the lavender odor is extremely strong, so much so that it can cause headache and nausea. It is also expensive and hard to find.
The safest solvent is Gamsol by Gamblin. It is the only solvent I have found or researched that truly has no odor (unless smelled directly), and is made for products that come into contact with the skin such as cosmetics and hand cleaners. It is a petroleum distillate and is highly flammable, but the aromatic solvents have been refined out of it (less than 0.005% remains). Aromatic solvents are the most harmful types of solvents. Given its true odorless qualities, it is the most widely used solvent in classrooms today. It is the only synthetic medium I use. I have found that it can also be substituted in mediums—meaning you can mix it with oils to make them more ‘lean’ without any adverse effects. If you are familiar with the Russian Academic 'triple-mixture', I have tested it and it is a perfect substitute for turpentine in that medium.
How to use Mediums
Art supply stores have many ready-made mixtures, but the best medium is one you can modify as needed based on what layer of your painting you are working on. For that reason, I use what Russian painters call a ‘triple mixture.’ This is made with 1 part oil, 1 part solvent, and ¼ part Dammar Varnish. For this mixture, Turpentine is the best solvent to use, but because of its odor some people avoid it. I have found that Gamsol works well as a substitute. I can use this mixture and increasingly add oil as I paint to make each layer more ‘Fat’ than the last.
Referring to the chart above, you can see there are many additives we can use to adjust oil content, drying time, consistency, and luster of our paints. If you love the science and experimental part of oil painting, you can dabble for years. Many oil painters do and they love it. If you just want to paint, the best way to begin (and perhaps continue) is keeping things simple. Following the ‘Fat-over-Lean’ rule gives us the guidelines below:
1st Layer | Paint mixed with solvent | Leanest |
2nd Layer | Paint straight from the tube | Oil content in paint |
3rd Layer | Paint mixed with medium | Oil in paint and medium |
4th + Layers | Increasingly more oil with paint | More oil added each layer |
Final Layer | Varnish | Apply to fully hardened paint |