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Friday, June 10, 2016

How Dyes and Pigments Differ

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By Jim Hingst 

 The chemicals that color our world, whether we are painting or digitally printing or decorating fabric, fall into two categories: dyes and pigments. Both types of colorants add color to materials ranging from wood, paper, textiles, glass, plastic, ceramic glazes and even concrete. Each type of colorant, however, is very different with respect to chemical composition, solubility, durability and color range.

In a nutshell, here are the key differences between dyes and pigments. Dyes are soluble; pigments are not. It’s the difference between a solution and a suspension (mixture).  What’s more, dyes have an affinity to the substrate that is being colored; pigments do not. Instead, pigments require a resin or binder in order for the paint or ink to adhere to the substrate. That’s it…almost! Of course, there are other differences.

Organic and Inorganic Chemical Composition

Regarding chemical composition, the first major difference is that dyes are usually organic compounds. What that means is that this material contains carbon. Many centuries ago pigments were primarily inorganic compounds, and did not contain carbon. Inorganic inks include cadmiums, metallic, oxides and opaque whites. Some pigments are comprised of heavy metals, which are toxic. Advances in paint and ink formulations have changed the chemistry of coatings. Today, pigments can be either inorganic or organic.

Solubility

Solubility is another distinguishing property. Dyes dissolve in a solution and become an integral part of that solution, which cannot be filtered out.  Some dyes dissolve in water, while others dissolve in alcohol or an oil based solvent.  The ingredients of the dye solution chemically combine. Pigments, on the other hand, do not dissolve in a solvent and are classified as insoluble.  Mixed with liquid ingredients, the solid particles never join chemically with these other substances.

Pigments are powdered colorants which in most cases are not soluble. When a pigment powder is combined with resin and solvent, the pigments remain as solid particles suspended in the liquid ingredients. Over time, the pigment particles can settle in a paint can or ink reservoir.

That’s why, if you are a painter, always stir your paint well before painting. All of the components must be dispersed uniformly in the mixture for optimal performance. Dispersion can affect how the paint wets out on the substrate and anchors to it. It can also affect the brilliance of the color and the durability of the coating.

Adhesion to the Substrate

Dyes bond or adhere to substrates in ways different from a pigment coating. Some dyes bond through a chemical reaction. Some dyes adhere to materials through absorption. Other dyes form an electrostatic bond. Pigments, on the other hand, require a resin or binder to adhere to the substrate.

Durability of Colorants

These larger molecules of solid powders help provide better durability than dyes, which are comprised of much smaller molecules. Used in paints and digital printing inks, pigments provide better UV resistance, better chemical resistance and are more stable when exposed to elevated temperatures than dyes are.

Synthetic Colorants

Our caveman ancestors produced dyes from plant materials, such as berries. Natural dyes were used for thousands of years, up until the time synthetic dyes were developed. With the creation of  synthesized dyes in the 1850s, natural dyes were nearly completely replaced by 1900. The synthesized products were not only less expensive to produce but the colors were also more durable and vibrant.

Most of the earliest pigments were ground up minerals. These were natural materials. However, pigments can be synthesized. In fact, one of the earliest artificial pigments was Egyptian Blue (CaCuSi4O10), formulated about 5000 years ago by baking copper containing minerals and sand. During the Industrial Revolution, the artist’s palette expanded with the addition of many new synthesized pigments.

Conclusion

Overall dyes have historically exhibited more vivid colors and are significantly less expensive than pigmented colorants. However, pigmented inks in the digital print world have improved to the point that they look just about as good as a dye ink. 

The primary advantage that pigments products have, are that they are more chemically resistant, more lightfast and provide greater longevity. In spite of their cost, pigment inks arguably deliver better performance in the signage and wide format graphics markets.

Here is a comparison of dyes and pigments: 

Dyes
Pigments
Soluble (inks are solutions)
Insoluble (paints and inks are suspensions or mixtures)
Small molecules
Large molecules
Significantly lower cost than pigments
More costly than dye-based inks
Poor UV resistance
Good UV resistance
Excellent color range; vibrant
Typically colors are duller as well as narrower color range
Environmentally friendly
Some pigments are comprised of heavy metals, which are toxic
Bonds to substrates using electrostatic charges
Requires a resin to bond to a substrate
Typically organic compounds
Inorganic and organic compounds
Limited heat resistance
Much higher heat resistance
Poor chemical resistance
Good chemical resistance
Limited durability; use for indoor applications
Good durability for use in both indoor and outdoor applications


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About Jim Hingst: After fourteen years as Business Development Manager at RTape, Jim Hingst retired. He was involved in many facets of the company’s business, including marketing, sales, product development and technical service.

Hingst began his career 42 years ago in the graphic arts field creating and producing advertising and promotional materials for a large test equipment manufacturer.  Working for offset printers, large format screen printers, vinyl film manufacturers, and application tape companies, his experience included estimating, production planning, purchasing and production art, as well as sales and marketing. In his capacity as a salesman, Hingst was recognized with numerous sales achievement awards.

Drawing on his experience in production and as graphics installation subcontractor, Hingst provided the industry with practical advice, publishing more than 150 articles for  publications, such as  Signs Canada, SignCraft,  Signs of the Times, Screen Printing, Sign and Digital Graphics and  Sign Builder Illustrated. He also posted more than 325 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published.  Vinyl Sign Techniques is available at sign supply distributors and at Amazon. 

Slides of Jim's Artwork

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