The vast majority of experiments in this area were made with additives — chemicals of various types that, when added to linseed oil, would cause the binder to set more rapidly. And the vast majority of those experiments ended up disastrously, creating an unstable paint film that had a tendency to crack, flake, peel, or just plain fall off the canvas. Needless to say, this was not particularly popular with art patrons of any time period! Some of the more successful attempts can still be found at art stores and purchased today: Cobalt Driers, Copal Mediums and Japan Driers to name a few, but even the most successful driers are still dangerous to the painting and must be used with care and precision to prevent unfortunate results and should not be used on professional work without a considerable amount of trial-and-error practice.
Fast forward to the 20th century, and the miracle of modern science which may have finally solved this sticky (literally) problem: Alkyd Resin! Alkyds are usually found in an additive —like Winsor Newton's Liquin or Gamblin's Galkyd brands — that is mixed directly with oil paints and are a chemical combination of polyester alcohol and fatty acids (hence the name: alcohol-acid, alkyd). Alkyd resins dry quickly, usually in 12-24 hours, and form a tough, flexible film that is completely transparent, which is very, very useful in oil painting for a number of reasons.So, first and perhaps most important, Alkyd helps oil paint to dry more quickly. Depending on the ratio of Alkyd to linseed oil (or poppyseed, walnut, etc.) and the strength of the pigment, an Alkyd/oil paint mixture can be made that will be opaque and dry within 1 day, which is a considerable jump on the usual drying time of 7-10 days for linseed oil. If the ratio of Alkyd is increased, then the resulting mixture becomes more and more transparent and will dry more quickly, which is great for glazing techniques.
The good news is that the glaze layers will oxidize separately, retaining the depth of color that is typical of the traditional oil painting technique. The downside is that too much Alkyd resin will create a look that is kind of like plastic (one of the main components is polyester after all), so keep those layers thin if you don't want your oil painting to start looking like an acrylic painting! Last, but not least, the Alkyd will form a film that is very flexible — much more so than standard linseed oil — so whenever you are painting with Alkyds, you can ignore the "fat over lean" rules. The Alkyd will be flexible enough to expand or contract as paint layers underneath are drying.
Overall, the invention and implementation of Alkyd resins has greatly improved the range of techniques available to the modern oil painter. While some traditionalists will eschew the use of this kind of additive because it has a modern look, it certainly remains the simplest and safest way to speed up the drying time of oil paint.
Some caveats and warnings will be useful here, however: Alkyd resins have only been in existence for several decades, so no one really knows if they will hold up in the long term. One of the great things about using purely traditional techniques in oil painting is that we know paintings done with those techniques have lasted for 500 years or more in the right conditions. With Alkyds (or acrylic paints for that matter) we have no idea if they will have that kind of longevity, although laboratory testing seems to indicate that they will.
The other, more important, consideration is physical safety: Alkyd resins are toxic, both from airborne fumes and absorption through the skin. Companies such as Gamblin have tried to make them as safe as possible, but the fact remains that you should take the same precautions with Alkyds that you would with turpentine. Work in a ventilated space, preferably with a fan or HVAC system that is moving air in and out of the room so fumes will not be able to build up.
If you are a messy painter, it would be advisable to wear gloves and otherwise cover yourself to prevent getting too much resin on your skin. If you do get it on you, no need to freak out, just wash it off thoroughly with soap and water. Given the proper safety protocols, you will find Alkyd resins a joy to work with and you will be the envy of oil painters through the ages!
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