By Jim Hingst
Paints are comprised of two basic components: a binder (or resin)
and a colorant (either a dye or pigment). Paint can also include a solvent,
which alters its viscosity. The combination of the binder or resin with a
solvent is sometimes referred to as the vehicle. In addition, paints can
also include a variety of additives, which modify its chemical and performance
properties. In selecting paints and pigments, several properties should be
considered, which are listed below:
Lightfastness. The lightfastness of
a paint or pigment describes how well it withstands degradation from UV light.
Artist paints in tubes are rated on a scale. In the United States, that scale
ranges from one (I) to five (V), with I being the most lightfast. The Brits use
a different scale from one to eight, with eight being the most lightfast. What
did you expect from the British? They still drive on the wrong side of the
road.
Heat stability. In outdoor
applications, the durability of a pigment is not solely dependent upon its fade
resistance in sunlight. The durability of the color is also affected to a large
extent on how it withstands elevated temperatures.
Toxicity. Many of the
traditional pigments were highly toxic. While most of these pigments have been
replaced by safer and less expensive synthetic pigments, some of the original
pigments are still available for conservators and the purists. One of the best
sources for natural and historical pigments and paints is the company, Natural Pigments.
Opacity or Hiding Power. Hiding power or
opacity of a paint or pigment is its ability to hide the surface that you are
painting. Selection of a pigment can be based on either its hiding power or its
translucency.
Color Temperature. Different pigments of
the same hue can exhibit varying color temperatures. This is one reason there
are many different choices for the same color. Cooler variations of a
colors tend to the cooler color spectrum of blue and greens. Warmer colors range
exhibit a warmer cast from yellows to reds. Even the differences among blacks
and whites are not black and white. For example, Ivory Black utilizes a
carbon black pigment, which is a much cooler color than Mars Black, which is
comprised of an iron oxide pigment. Flake white, which has a yellowish cast, is
much warmer than the brighter titanium white or the cooler bluish zinc white.
Tinting Strength. Tinting strength
describes the ability of a pigment to change the hue of another color. In part,
tinting strength results from the concentration of the pigment in its vehicle.
What also affects tinting strength are the actual physical properties of the
pigment, such as its transparency as well as how a pigment absorbs certain
light wavelengths and reflects others. Particle size and dispersion also play a
role. The bottom line is that two different pigments for the same color may
exhibit dramatically different properties. You can visually compare the tinting
strength of two paints by mixing equal amounts of the color with equal amounts
of titanium white. This may not be very scientific compared to using lab
instrumentation, but it should do for the painter in the field.
Chemical Resistance. The color of a
pigment not only can fade, but its hue can also change. Exposure to acids and
alkali, heat and air pollutants can actually darken some pigments. Some
pigments darken as a result of oxidation or a reaction to other elements in the
atmosphere. When I was working for a vinyl film manufacturer, I investigated a
product failure in which a bright red film darkened to a burgundy hue. Any
number of factors could have affected this color change, including heat and
oxidation.
Using Linseed Oil to Make a Medium
Why Paint Wrinkles
How to Clean Brushes Used for Water-Based Paints
Proper Prep Prior to Repainting Walls
Coating Woodworking Projects with Epoxy Resin
The Practicality of Repainting an Old Acrylic Sign
Acrylic Mediums & Additives
Acrylic Glazes
Finishing Tips
Blending Colors
Making Oil Paint
Zinsser Bulls Eye 1-2-3 Primer
Mediums for Oil Painting
Faster, Easier Paint Clean Up
Penetrol Paint Conditioner
Shades of Black
Flesh Tone Paint Recipe
White Lead Oil Paint
Safely Working with Pigment Powders
When to Thin Paint with Naphtha
Damar Varnish Recipe
Fat Over Lean Rule
Applying a Wiping Varnish to Your Carving
Asphaltum
Essential Solvents for Sign Painters
Traditional Gesso Recipe for Encaustic Painters
Painting with Gouache
Epoxy Resins
Bondo Tips
Flattening Paste for Enamel Paint
Paint Chemistry Terminology
Scratching the Surface with Grey Scotch-Brite Scuff Pads
© 2016 Jim Hingst
