Discussion of pigments and the hiding powers of a fresh coat of paint from a Washington, DC area contractor
Standing facing a deep evergreen-colored dining room with a gallon of interior flat paint tinted a nice, neutral cream, you expect to face some challenges regarding coverage. Meaning, you expect that your first coat of warm cream might have some strange greenish undertones showing through the new topcoat. What you might not expect is that the same issues also come up in the opposite scenario: when you have white trim, say, and you want to paint it a deep navy blue. Whenever you paint over a color that has a drastically different value than your chosen shade, you will run into problems with coverage.
What is the meaning of the word value, in the paint lexicon? Well, value is one of three characteristics used to classify color, and it refers to how light or dark a given shade is. If you could imagine taking three teaspoons of blue paint, and mixing thirty drops of white into one, thirty drops of black into the second, and thirty drops of gray into the third, then you can picture three shades of blue with three different values: one dark, one light, and one neutral. The other two characteristics of color are the hue, which describes the actual color on the basic wheel (i.e., red, orange, yellow, green, etc.), and the saturation, which describes how much the shade has been dulled by a hue-neutral color (like black, white, or gray). The hue of a color is obviously of utmost importance in the color’s final impression, and the saturation, which is a measure of how bright or dull a color is, also plays a very strong role in the aesthetic effect. When it comes to coverage in a paint system, however, the difference between the values of the existing paint and the new topcoat is the factor that most greatly effects how much the undercoat will show through.
The reason that value plays such a strong role in coverage is that the value of a color is the measure of how much light that color reflects, and how much it absorbs. If an undercoat has a lighter value than the new paint, any gap in the fresh paint will reflect a significant bit more light, and stand out from the overcoat – and vice versa for an undercoat with a much darker value than the new paint.
The keys to adequate coverage, therefore, are:
1) Pick a primer that is the same value as your new shade of paint. If you are painting a pastel over a dark color, prime it with white; but if you are painting a dark color over a light one, you need to find a primer that comes in a shade of gray that is the same value as the new color.
2) Buy high-quality paint. Paint has four components: the binder, the pigments, the solvents, and the additives. The solvents are usually clear fluids, the additives invisible chemicals, and the binder a clear, sticky, film-forming substance that provides the physical framework for the new coating. But it is the pigments that give the paint its color – and its opacity. While there has always been a wide array of options for black-hiding (i.e., creating an opaque coating out of dark colors), it has only been in the past 100 years that paint technology has progressed to allow for safe, effective white hiding, which is the use of light-colored pigments to create reflective opacity. The advent of titanium dioxide, an oxidized metal that has become both cheap and effective at creating strongly opaque pastels, created a class of paints that made white hiding truly be an option. Cheaper paints will not have much true titanium dioxide in them, though; they will be full of cheaper, less effective substitutes called “filler pigments”. Filler pigments add to the bulk, but not the opacity, of the film coating, and therefore lead to lower quality paint.
3) Prepare your surface adequately and use proper equipment. If your primer values match, and your paint is high quality, but you are still seeing through your new coating, you might be failing somewhere in the execution. Make sure that your brushes and rollers are high quality and well-matched to the job, and also make sure that your surface has been adequately cleaned, sanded, and scraped prior to application- especially if it is gloss or semi-gloss!