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Why Make Oil Paints Dry Faster?
Oil paints are a pleasure to work with. They are usually of a buttery consistency, but they could be slightly thinned so they can be spread more evenly. Oil paint dries slowly, allowing brush marks to self level. Also, a slow drying time allows for additional working between paint layers. Many oil painters paint wet over wet.
So why speed up the drying process of oil paints? There are a few main reasons.
- First is the "fat over lean" principle. Paintings are always multilayered to give depth. Applying the first layer thinned with solvents (lean) or alkyd medium allows this layer to dry quickly so an oil-rich paint layer (fat) can be easily applied.
- Second, faster drying may help if oil paints have been applied to non-porous surfaces like metal sculptures. Canvas and boards can absorb some of the paint, providing for better adhesion and drying. But on primed metal, all the paint rests on top of the applied surface. A faster dry time would allow multiple layers to be applied more quickly and the sculpture can be handled or worked on again sooner.
- Third, different pigments have considerably different effects on the drying of oil paints. For instance, cobalt blue and iron oxide pigments actually act as siccatives, speeding up the drying of oil paints considerably. Other pigments, such as cadmium red and carbon black, slow down the drying time of oil paints to the point where it can take several weeks!
- Lastly, there are different kinds of artist grade drying oils such as linseed, walnut, and safflower. The last two oils mentioned are more pale and much less prone to yellowing than linseed oil. These oils are best for white and yellow pigments. These oils, in being less reactive than linseed, take much longer to dry than linseed oil.
Now let's look at five additives that help oil paint dry faster.
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Pure Gum Spirits of Turpentine
Good old turpentine is a traditional solvent that has been used to thin oil paints and clean brushes for generations. It also helps dry paints faster. It does this because of the resinous nature of turpentine. Also, the physical aspects of thinning the oil paint cause it to spread out into thinner layers, which aids in drying. This is the lean part of the “fat over lean” principle so often mentioned in oil painting tutorials.
Damar Resin Medium
Damar is a hard pale yellow tree resin that is soluble in turpentine but not mineral spirit. This is when it's added to turpentine in the ratio of 100 grams resin to 200 ml turpentine. When used sparingly, a resin oil paint is created that dries to a harder film and increases gloss. Typically no more than 20% of total resin paint should consist of damar medium.
Heavy Metal Siccatives
Metallic siccatives are heavy metal salt compounds dissolved in petrol distillate solvent base. These are mostly supplied as cobalt and/or manganese naphthenates, but other metals like strontium can be used. Strontium siccatives are usually clear and useful for light colored oil paints.
Heavy metal siccatives work as metal catalyst that speed up the oxidation of the drying oil, hence causing the paint film to form faster.
Paraloid B67 Resin Solution
Paraloid B67 is an acrylic resin that is soluble in mineral spirits and VM&P naphth when at least 10% aromatic solvent such as xylene or toluene is added. It is fully compatible with drying oils and adds harder and glossier paint films. Usually, 25% of total medium volume is more than adequate.
It should be noted that Paraloid B67 solution is mostly solvent since resin content is usually less than 50% weight per volume. Therefore, this resin is not able to hold very much pigment on its own. If making oil paint by hand, it is recommended that the appropriate amount of oil for the particular pigment be measured out before intermixing any Paraloid B67.
An alkyd medium is an oil-based medium that dries much like traditional drying oils like walnut and linseed oils. Alkyds are petrochemical modified drying oils that are more reactive and hence faster drying. This offers a relatively solvent free experience for the oil painter who objects to using turpentine or turpentine based mediums. Furthermore, alkyd mediums are a type of drying oil that dries to a flexible finish like other oils. This means they are less prone to brittleness that some resin additives.