What’s in Paint?
Something within our human nature compels us to paint. Ever since our primitive ancestors decorated the walls of their caves more than 40,000 years ago, man has formulated different types of paint mixtures.
In all that time, the basic components have remained the same. Regardless of what type of paint it is, paintconsists of four major components: (a) the solvent; (b) the binder or resin; (c) pigments or dyes; and (d) additives.
The solvent, which is also referred to as the diluent, dissolves or dilutes the resin and modifies the viscosity, thereby adjusting the flow characteristics of the paint. The solvent is a volatile liquid, such as methanol, naphtha, toluene, acetone, ketone or water, which evaporates after the paint is applied, leaving just the dried paint film. In no way does the solvent become part of the finished paint film. Some will categorize paints as either solvent borne or waterborne, although water is a solvent.
The binder or resin is the glue that holds all of the remaining components together, after the paint dries. Without the binder, emulsified pigment would just dry on the substrate and return to dust and blow away. The typical types of binders that are used in modern-day waterborne paints, also referred to as emulsions, include latex and acrylic.
In bygone years, casein, lime and egg yolk, were also used as resins. Casein is a milk protein used in making milk paint. (See my story: Toning Gilded Surfaces with Milk Paint.) To make the base resin for egg tempera, you simply mix two parts egg yolk with one part dry white wine. After blending ground pigment with a little water, the egg tempera base is mixed in. Voila! You now have paint.
While most of the paints used for sign lettering are solvent based alkyd enamels, Ronan’s Aquacote is an “environmentally-friendly” waterborne alternative. Aquacote paints utilize an acrylic resin as its binder. The advantage of acrylic is its fast drying time. If you decide to work with these you will need brushes dedicated specifically for these paints.
When latex paint was developed in the 1940s, it actually had latex in it. Today there isn’t any latex in latex paint. Latex is one of those catch all terms that includes a wide range of resins, such as acrylic, vinyl acrylic, styrene acrylic, polyurethane, polyester and polyvinyl acetate.
The best “so-called” latex paints are 100% acrylic latex. The best paints will also be the most expensive. As with other waterborne paints, latex is less hazardous and more eco-friendly. It also dries fast. And once it dries, it is durable. One reason that the acrylic latex paints are durable is that they are very elastic. That way, as the substrate expands and contracts, so does the paint. Compared to oil based paints such as enamels, the surface finish of latex paints is not so smooth or glossy. The color of oil paints is arguably more vibrant, because the paint holds a heavier concentration of pigment.
Typical resins used in the manufacturing of solvent-based paints include natural ingredients such as linseed oil and walnut oil and synthetic ingredients, such as epoxies, polyurethanes and alkyd resins.
In the 1500s, oil paint replaced tempera and remained the popular choice among artists until today. Artists’ oil paints are not much more difficult to make than egg tempera. Until the twentieth century all artists ground their own pigments and made their own oil paints. After grinding pigments, linseed oil was blended in to form a paste. The ratio of pigment to oil ranges from 3:1 to 1:1. The more oil that you use, the longer that it takes for the paint to dry. If you need to adjust the viscosity of the mixture, you just add some solvent.
After painting, the solvent evaporates and the molecules of the binder or resin fuse together and harden. The process by which the binder cures differs from one type of binder to another. Some resins cure through oxidation. Others cure as a result of evaporation. Polyurethanes, on the other hand, use a catalyst to initiate polymerization.
The third major ingredient of paint is the pigment. Unlike a dye, which can dissolve in the solvent, pigments are granular solids, which do not dissolve. This is the component of paint that gives it its color and its opacity. Some of these pigments are natural ingredients, such as clays or semi-precious stones. Other pigments are synthetics.
The opacity of the pigment is important for a couple of reasons. First, the pigment blocks ultraviolet light from shining on the substrate, thereby preventing the UV rays from degrading the surface. Second, the opacity of the pigment is important, because it prevents a distracting background from showing through, detracting from the impression that the sign artist is trying to create.
The last group of paint components includes the additives. These ingredients include thickeners, flatteners, adhesion promoters, driers, anti-fungicides and flow agents.
Altering the Properties of Paint
Of course, on the job you can alter the performance properties of paints with your own additives. Some of the popular additives that sign painters use include:
Penetrol® Oil Paint Conditioner. Sometimes described as a paint thinner, Penetrol is better classified as an oil that conditions the paint and improves the flow characteristics of the coating. Chromatic Edge, which the 1 Shot Paint Company manufactures, is a similar product. When mixing up their paint, many pinstripers will add equal amounts of thinner and Penetrol. By adding a little Penetrol (up to 10%) to the paint and using using turpentine rather than mineral spirits as a thinner, many painters believe that the paint flows out more smoothly, and your brush has less drag when either palleting your brush or painting. Using a paint conditioner, such as Penetrol, also minimizes telltale brush marks, because the paint more readily levels out. Try adding Penetrol to the paint on those sweltering hot summer days, when the paint tacks up too fast. The Penetrol will act as a retarder and slow down the drying time as well as help the flow of the paint.
Note: Just like paint, Penetrol can develop a skin on the surface. For this reason, you may want to pour your Pentrol into an 8oz. plastic squeeze bottle and store it upside-down so that any skin that forms is on the bottom of the bottle.
Reducers. For thinning lettering enamels always use the reducer that the paint company recommends. 1-Shot Reducers are formulated specifically for their lettering enamels and will lower the viscosity of their paints and help the paint leveling. When working in colder temperatures, use a low temp reducer to accelerate the rate of evaporation. When temperatures are hot, the solvents in the paint evaporate quickly causing the paint to tack up. To slow down the rate of evaporation, use a high temp reducer. When working in normal conditions, use 1-shot’s standard reducer.)
Turpentine. Other than a paint manufacturer’s own reducers, the next best thing for thinning lettering enamel is turpentine. Be aware that compared to mineral spirits, turpentine is more toxic.
Mineral Spirits (or White Spirits). For thinning any alkyd paint, many pinstripers and sign painters use mineral spirits. Also use mineral spirits for rinsing your brushes between colors or for general clean up.
The performance properties of mineral spirits are similar to those of turpentine. Mineral spirits is used more and more today because, it is less toxic than turpentine. As a word of caution, mineral spirits are a blend of a variety of solvents, all of which are made by refining petroleum. This mixture of solvents varies greatly from one manufacturer to another. My point is that you never know what you are getting. What’s worse, is when you use mineral spirits to thin a lettering enamel, the results that you get can vary too. Although many painters use mineral spirits to thin their paint, turpentine or the paint manufacturer’s reducer is a better choice. Enamel reducers, which consist of (Toluene, Aliphatic Naptha, Acetone, Butoxyethanol, Methanol, Xylenes and Ethylbenzene), are formulated specifically for thinning enamels. These reducers can also be used to clean your spray gun.
Naptha. To speed up drying times, naptha is sometimes used because it evaporates very quickly.
Driers. The evaporative process causes an oil paint to dry. Curing, though, is a completely different process. Curing refers to the polymerization of the resin, which occurs as the paint oxidizes and simple molecules crosslink to form more complex molecular structures.
By attracting oxygen into paint, a cobalt drier accelerates drying times. When adding any drier to paint, use care. As little as a drop or two added to a medium is all you need. As a rule of thumb, limit the amount of drier to less than 5%. Adding too much drier can cause problems, such as wrinkling, yellowing and cracking. Cobalt driers can also alter the hue of paints, especially white.
Flattening Paste. Lettering enamels have a high gloss finish. Painters, who are trying to create an antique look, will occasionally add mix in 1 Shot/Chromatic clear flattening paste to their paint. The flattening paste will deaden the gloss level and achieve a flatter finish when painting with 1 Shot lettering enamels or bulletin colors. The gloss level will vary depending on how much is added to the paint. Do not add more than 50% of the flattener. Also be aware that as you increase the concentration of the paste, the paint will become less and less opaque.
Fisheye Eliminator. Adding a fisheye eliminator, such as Marson’s Smoothie, to your paint can help prevent fisheyes. An 8oz. bottle of Smoothie costs between $15 and $20. It is ironic, though, spraying a previously painted substrate that has some fisheye eliminator residue on it can also cause fisheyes. When painting a vehicle substrate, paint companies generally recommend against adding fisheye eliminator to base coats. If fisheyes appear in a painted surface, there’s not much that you can do other than sand the affected surface until the little craters disappear.
Solvent Safety. Many of the solvents used in painting are hazardous. Before using any chemicals, always read the labels and the manufacturer’s instructions before use. Properly dispose of any waste materials. Store all flammable materials in a safe manner. Handle all hazardous materials safely and wear appropriate safety gear when warranted.
When you are not using a can of solvent, put a lid on it to prevent the vapors escaping into the air of your shop. If you happen to knock a can of solvent over, clean up your spill immediately. Don’t eat, drink or smoke while you are working with chemicals. And wash your hands with soap and water (instead of using solvents to clean your hands) after painting or working with solvents, before you eat.
If you are spray painting or airbrushing, always wear a respirator. If you are working with urethanes, you need to wear a hood and use a fresh air respirator. Even if you wear a respirator, work in a well-ventilated area. Paint fumes are hazardous to your health. Solvent fumes are also flammable. Make sure that when spraying solvent-based paints that no smoking is allowed or no open flames are present.
When you are painting, always wear latex gloves. If you get paint on your hands, you don’t need to clean up by washing in lacquer thinner or other solvents. Art Schilling told me an interesting little tidbit of safety information. Blood vessels are located very close to the cuticles of your fingers. When you dip your hands in solvent, it enters your blood stream and in fewer than 30 seconds, the solvent reaches your liver.
Instead of washing up with mineral spirits or lacquer thinner, wash up with soap and water. If that doesn’t clean off the paint, rub some baby oil on your hands to help in cleaning up.