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Saturday, July 9, 2016

The Facts about Drying Oils for Painting

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                                               By Jim Hingst @hingst_jim

Differences Among Types of Oils Used in Fine Arts Painting

Artists use different types of drying oils for painting. These oils could be rated based upon appearance, yellowing over time, wetting properties, drying time, cost, etc.

Linseed oil is classified as a drying oil. Other drying oils used in fine art painting include walnut oil, poppy oil, sunflower oil and safflower oil. Oil paints do not dry by evaporation. Instead these paints cure as the oil in the paint oxidizes. How fast paint actually dries depends on a few variables. These include the type of linseed oil used, the thickness of the paint and the pigments in the paint mixture.

           Refined Walnut Oil




Linseed oil, which comes in many forms, is the most widely used oil in fine arts oil painting. It exhibits many fine features. Its downside is that it has a yellowish or brownish color, which can darken with time.

For this reason, many artists will use other alternative oils, such as poppy oil, when painting with bright colors or white. To compensate for this shortcoming, manufactures may refine or bleach the oil. Processing, however, will alter the physical and performance properties of linseed oil.

When oils are mixed with paint, they modify the performance of the paint. These oils can alter how a paint flows. They can modify its gloss level. And they can make a paint more transparent or opaque.

Linseed oil, which is pressed from flax seeds, comes in various varieties. It can be cold pressed, boiled and refined. How the oil is processed determines the properties of the product.

The old masters are generally believed to use cold pressed oil. This belief is challenged by some scientists today. One reason that there is disagreement among professionals in the field is that artists have traditionally kept their paint formulas a secret. That’s understandable. No modern day paint manufacturers would reveal their secrets.

Cold pressed oil that was used hundreds of years ago was not subjected to steam or solvents to extract the oil. The flax seeds were milled similarly to the way grains were milled. It is natural state, cold press oil is yellowish in color. The color can vary for a number of reasons. Impurities can vary from one processor. For this reason, cold pressed oil is sometimes aged to allow the impurities to settle.

Cold pressed linseed oil dries more slowly that other forms of linseed oil. Some artists find this slow drying characteristic an advantage, because it allows the paint to level out, which eliminates brush marks.


Heating Cold Pressed Oil


Rembrandt, for example, is believed to have heated cold pressed linseed oil to a temperature of 390°F (200°C). Heating the oil promotes a chemical process called oxidative polymerization.

Here’s what happens. Linseed oil on its own will oxidize. Heating just speeds up the chemical process. In this oxidative polymerization process, an oxygen attaches itself to the small monomer molecule. The oxygen atoms have an affinity for one another and join together to form long polymer chains.

This process is of monomers joining together to form long molecular chains is called polymerization. After polymerization occurs, these large molecules will crosslink. 

Crosslinking is the process in which polymer chains chemically bond together. The crosslinking makes the linseed oil very stable, very hard and less likely to yellow over time.

The practical result from heating  for the painter is that the oil becomes thicker and cures faster. Used for paint formulas, the oil was not thick enough to create impasto effects. Rembrandt also mixed in additives into his paint, such as chalk and ground sand. The pigments that he use were also not milled so finely as those used in today’s paints. Artists of that period also added metal oxides, such as lead oxide, to their paint formulations to speed drying.

The type of heated linseed oil that Rembrandt used is not the same as the boiled linseed oil that you would buy at the big box stores. In manufacturing boiled linseed oil, it is heated and mixed with chemical driers. While using boiled linseed in a medium could accelerate drying time and produce a glossy finish, the shortcoming is its yellow appearance and its tendency to darken over time. For this reason, only use boiled linseed oil, if you use it at all, for underpainting.

Boiled linseed oils does have its uses. The old time sign painters would also use it to preserve wooden tool handles and ladders. I have used it for this purpose, too. It works great. For this application, mix 50% turpentine with 50% boiled linseed oil.

Another way that the old masters processed raw linseed oil is to expose it to sunlight for several months. This accomplishes two things. UV light will bleaches the yellow oil. The second effect is that the oil oxidizes which thickens the oil.

Stand Oil

Stand oil is linseed oil that has been polymerized by heating. 

For making an artist’s medium, use stand oil. Stand oil is linseed oil that has been subjected to high heat in the absence of oxygen for a couple of days. Because the oil has not oxidized, it cures very slowly.



Compared to other forms of linseed oil, the slightly colored stand oil is very thick. For this reason, it must be thinned with turpentine or mineral spirits, when you use it to make a medium. Yellowing of stand oil over time is minimal. Be aware, though, all types of linseed oil will yellow to some degree. With stand oil, the yellowing is slight, which is why it is so popular among artists for glazing mediums.


Other Drying Oils


Many artists prefer also using walnut oil for making mediums. It is a good clear drying oil that dries faster than other oils.

Compared with linseed oil, walnut oil is clearer, but it does have a slight yellow cast. It also yellows less than linseed oil with age. Walnut oil is a thin oil. Added to paint, its relatively low viscosity allows the paint to flow more readily and to dry within five days.

Poppy oil is very popular among artists today. It is a clear oil that does not yellow as much as linseed oil. The disadvantage of poppy oil is that it dries more slowly than linseed oil. More importantly, it is not as durable. As a word of caution, if you use poppy oil in a painting, do not use a linseed oil glaze over it. The linseed oil will dry faster than poppy oil. The result will likely be cracking.

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About Jim Hingst: After fourteen years as Business Development Manager at RTape, Jim Hingst retired. He was involved in many facets of the company’s business, including marketing, sales, product development and technical service.

Hingst began his career 42 years ago in the graphic arts field creating and producing advertising and promotional materials for a large test equipment manufacturer.  Working for offset printers, large format screen printers, vinyl film manufacturers, and application tape companies, his experience included estimating, production planning, purchasing and production art, as well as sales and marketing. In his capacity as a salesman, Hingst was recognized with numerous sales achievement awards.

Drawing on his experience in production and as graphics installation subcontractor, Hingst provided the industry with practical advice, publishing more than 150 articles for  publications, such as  Signs Canada, SignCraft,  Signs of the Times, Screen Printing, Sign and Digital Graphics and  Sign Builder Illustrated. He also posted more than 400 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published.  Vinyl Sign Techniques is available at sign supply distributors and at Amazon. 

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