Advanced Paint Technologies for the Artist
What most painters don't know about paints
Most artists have a knowledge of the different types of polymers that are commonly used in artist paints: drying oils, acrylics, alkyds, beeswax (encaustic), egg (egg tempera), milk (casein), and others. But there are less-known factors, nearly as consequential, which also greatly effect the strength, durability, and general characteristics of paints. Although artists don't learn about these factors in art school, a basic knowledge about them can be helpful.
Only slightly secondary to a paint's polymer type in determining its properties is its method of curing. Curing, or "drying", is the process by which a coating changes from a liquid to a solid. In the liquid state, a coating consists of relatively small sections of polymer molecules. Polymer molecules are large, repeating chain-like structures. It is only during the curing process that these small molecules bind together to form the large macro-molecules that the paint film will be made of. In effect, the last stage of manufacturing paint does not take place until it cures. The liquid material that comes out of a can or tube is only a precursor material to the finished paint.
How this curing process takes place – how the small segments of the polymer join together into larger chains – determines a great deal about the properties of the dry paint film. In general, polymers whose macro-molecules are larger and more strongly bound together form stronger and more durable paints. The curing processes of paints are characterized as "low energy" or "high energy", with higher energy cures resulting in stronger bonds. High energy curing – characterized by powerful and active molecular bonding – results in more and stronger intra-molecular bonds as well as in longer molecules. High energy curing also helps the paint to bond more agressively with the underlying surface, again creating more and stronger bonds between the two.
Most artist materials rely on low-energy curing. For example, oil paints cure by a process of slow oxidation, a low-energy cure, in which the short polymer molecules in linseed oil combine with oxygen to form a new material, linoxin, which makes up the solid material of dry oil-paint. Most artist paints dry by evaporation. The solvent (water, mineral spirits, etc.) in the wet paint keeps the small sections of polymer molecules apart. Only when the solvent evaporates are the molecules free to bond together to form the finished polymer. Polymers whose small segments are very powerfully attracted to each other require stronger (and usually faster-evaporating) solvents to keep them in a liquid state; they generally form larger and more strongly bonded polymers when they cure. Laquers, for example, cure with a higher energy than mineral spirit based enamels.
It used to be common for coatings in industrial situations requiring strong paint films to rely on powerful solvents to achieve strong high-energy cured polymers. In the last several decades however, revolutionary changes have occurred in the coatings industry. New technologies, often spurred on by environmental regulations for eliminating solvents, have resulted in amazing new types of high-energy coatings. Like earlier baked-on industrial coatings – which add heat energy to the curing process in order to form very strong paint films – these new processes bring additional energy into the curing process to gain strength. UV cured paints and electron-beam (EB) cured paints, for example, focus direct energy sources on the paints to cure them. Two-part, and catalyst-cured paints – epoxies are a well known example – mix together separate components to make strong chemical reactions which powerfully bond the polymers.
Many, if not most, manufactured objects today are never coated with wet paint at all. Powder-coating technologies instead utilize static-electricity to adhere dry powdered resins and pigments to the objects being coated. They are then baked at high temperatures to melt and fuse the coating materials onto the objects.
These technologies allow paints to be made of resins which once required very strong solvents, or which could not previously be made into paints at all. Urethanes, polyesters, epoxies, and other new materials are now among the strongest and most durable paints available.
When Ralph Mayer wrote The Artist's Handbook – still often considered the standard text on art supplies – many of these paint types were not yet even invented. Today, these new coatings and technologies are accepted standards wherever strong and durable industrial coatings are needed. But don't expect to see them turning up in art materials any time soon, except in special cases. Besides the fact that artists and art supply manufacturers are traditionally slow adapters of new materials, most of these paints require factory environments and equipment for their use. Still, certain specific art applications lend themselves beautifully to these technologies.
One such instance is in advanced primers for wooden art panels. Hudson Highland's PRIMEWOOD™ panels use a catalyzed and heat cured urethane primer. Urethane coatings are prized for their strength, durability, and longevity. They also form the tightest vapor barriers of any durable coatings. They possess a degree of natural resilience which makes them highly resistant to cracking. And by using a high-energy curing formulation, these properties are amplified. The high-energy cure also allows them to bond to the surface of the wood panels with incredible strength. For all these reasons, no other primers – not acrylic gesso, oil primers, alkyds, or traditional gesso for panels – even come close to the advantages offered by PRIMEWOOD™.