The Use of Solvent in Oil Painting

The correct (and safe) use of solvent sometimes confuses artists who are new to the medium of oil. I certainly didn't know too well what I was doing when I started.

This post is to help those (principally my students) navigate the use of this stuff.

The historical solvent used for oil painting is traditionally turpentine which is distilled from the resin of pine trees. (Probably your favorite painter from the 19th or early 20th century used it.) However, it has some significant health issues. People can develop an allergy to it, and it can generally bother the eyes and respiratory system. It also has a pretty strong smell.

Nowadays we have products like Turpenoid and Gamsol which can take on the same functions in the world of oil painting, specifically thinning paint for an initial application, and cleaning brushes. They are both principally distilled from petroleum and have far less of an odor than true turpentine. Some people seem to think Gamsol has a bit less of a smell to it than Turpenoid. There are other products out there as well, but I will only speak to ones I have used.

I personally use Turpenoid. (for now, anyway)

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Uses:   Cleaning of brushes

The common cleaning method for brushes used with oil paint is this:

1. Wipe most of the excess paint off on a rag or paper towel

2. Clean the brush in solvent and them wipe on rag/towel

3. Clean with soap and water, rinse, and form bristles back into original shape

This shows how using a jar with a raised screen (on the right) keeps you from shoving your brush back into the pigment that collects at the bottom (as on the left)

Here are some of the common types of brush cleaning jars (photographed at Michaels):

Recycling & Disposal

I practically never throw out/dispose of solvent.

My method is this: When my brush washing jar gets too much buildup at the bottom and is just too polluted with pigment, I shake it up (with the lid well-screwed on, obviously) and pour that filthy stuff out into a 2nd jar. I will then wipe out the brush washing jar and put some clean solvent in.

I let the 2nd jar (call this one "dirty solvent") sit undisturbed until all the pigment has settled at the bottom (maybe a week). Then I pour off the (relatively) clean solvent into a 3rd jar (call this one "recycled solvent"). The recycled solvent can then be used again. It may not be quite as clear as fresh solvent, but it is close enough for my purposes.

The dirty solvent jar becomes a holding area to let the pigment settle. At some point, the 2nd/dirty solvent jar will get too full of pigment gunk from many uses. I then (after pouring off any usable solvent) let it sit without a lid in my garage until it has all dried out and the pigment solidifies. Then I throw it out and start a new one.

To be clear: it's a very bad idea to dump solvent of any kind (Turpenoid, Gamsol, etc.) down the drain. If you need to get rid of some, contact a recycling center near you. There are places that will take that kind of thing.

Thinning paint for initial "washy" application

Many painters like to put an initial washy layer down, using solvent to thin the paint. (This can kind of look like watercolor.)

This is fine, providing you only use solvent at this stage.

It's bad practice to continue thinning paint with solvent as you work, building layers. If you need to add something to your paint in the later/upper layers, use a medium of some kind.

Health Issues

Even though modern solvents such as Turpenoid and Gamsol are healthier to be around (breathing-wise) than Turpentine, they still need to be used in a well-ventilated space.

If your studio is on the small, or poorly-ventilated side, there are things you can do. Opening a window helps, along with generally trying to get some air moving through your work area. I often put the lid back on my solvent jar when I am not regularly needing access to it.

There are also alternatives to using solvent.

Some artists use linseed or other oils for cleaning, citrus-based products, or Lavender Spike Oil. I've been considering something like these, but have not tried them yet.

Mediums & Oil Painting

On using Medium in Oil Painting

The way I see it, there are three principle reasons to add medium to your paint while working:

• Increase Transparency

• Alter the Viscosity

• Alter the Drying Time

I'll talk about these in a moment, but first of all remember:

    • You don't have to use medium at all. If you do, be thoughtful about it.

    • Observe the Fat over Lean rule:

Fat over lean means to use less medium at the start (ideally none, just thinning with solvent if needed) and use more medium (if desired) as you work on top to the finish. The issue is with varying drying times and potential cracking over the long-term if done the wrong way around.

Think of medium/linseed oil as fat, and straight paint [with or without solvent] as lean.

I am going to try and restrict my comments here mostly to mediums I have personally worked with. There is a lot out there.

Increasing Transparency

If you want to get into laying a transparent "veil" of color over an area of dried paint, you will probably want to add something to your paint. The opacity of paint varies by the pigment, but for glazing, an additive is usually needed.

Most kinds of medium will accomplish this. Linseed oil will do the job. An alkyd-based medium like Liquin or Galkyd will do so while also speeding up the drying time.

Altering Viscosity (Thinning or Thickening)

Thinning the paint for increased "flow" is a common reason to add medium. Rendering certain kinds of things works better when the paint flows more. Linseed oil will do this, as will some of the variants of products like Liquin or Galkyd.

Oil paint is pretty good at holding marks when you want to paint in an impasto manner. ("Impasto" just means a thick paint application.) But sometimes painters want even more body and for that purpose there are so-called impasto mediums. Rublev/Natural Pigments makes one, though I haven't tried it yet. Winsor and Newton makes a version of Liquin called "Liquin Impasto Medium" which I have not used myself.

Altering the Drying Time

Depending on the color/pigment, oil paint can take days, or even up to a week to dry. That can be frustrating. Alkyd-based mediums like Liquin or Galkyd will generally halve the time most colors require to dry. Other factors affect drying time too, like light exposure and air circulation. A painting in a sunny room with good air circulation will dry faster than one in a dark, unventilated space.