Alternative Pigments Are Becoming Available

Introduction
Environmental and health concerns have spurred increasingly stringent regulatory requirements for the use and disposal of Cadmium based pigments. As a result, many industries have decreased or entirely eliminated the utilization of these colorants. If these trends continue, formulating cadmium pigment into artist paints will become increasingly difficult, and ultimately, may be impossible due to lack of availability. However, the introduction of newer organic pigments has made finding suitable alternatives easier than ever. While not identical to cadmium based pigments, their properties are similar enough in some respects, and superior enough in others, to warrant consideration. Golden Artist Colors, Inc. has recently introduced three such colors; Hansa Yellow Opaque, Pyrrole Red Light, and Pyrrole Orange. Also in this group is Pyrrole Red, which was first made available by GOLDEN in 1990.

Cadmium pigments were discovered around 1820 and first commercialized for artists’ use by the mid 1840’s. Although Claude Monet used them extensively in the 1840’s and 50’s, the scarcity of the metal kept their use relatively limited in artists materials until the 1920’s. Their introduction provided unequaled hues in the yellow to deep red range, in terms of brightness and lightfastness.

Cadmiums offered new color intensity and opacity While cadmium pigments are considered extremely lightfast under conditions of indoor use and exposure, they fade a great deal when used outdoors in acrylic paints. For this reason, they should not be used in exterior mural painting. The difference between indoor and outdoor performance is thought to be due to the combination of environmental factors encountered outside; moisture, ultraviolet radiation and air. These cause bleaching induced by oxidation of the cadmium sulfide to cadmium sulfate. That is why the water permeable acrylic vehicle is prone to this effect, while cadmium pigments used in impermeable binders, such as rigid plastics, are not.

Industrial Use
Only 5-7% of total cadmium pigment production is used in the manufacture of artist materials. Since most is used elsewhere, clues to future availability may be found by looking at what is happening with the higher use industries.
Cadmium pigments excel in high heat applications, as encountered in the glass and injection plastics industries. Although the performance of cadmium pigments in the glass industry may be unequaled, their use is prohibited to a large extent due to the “Toxics in Packaging” laws of many states, which limit the intentional additions of heavy metals to packaging materials. Glass is manufactured primarily as a packaging material. These restrictions have also impacted plastic packaging, but not applications known as “engineered resins” which encompass such uses as injection molded handles and housings for lawn and power tools. These are high heat applications where the cadmium pigments continue to outperform organics due to their heat stability.

Another industry which has declined drastically in cadmium pigment use is automotive manufacturing. Whether it is a matter of color fashion, with earth tones favored over a bright red interior, or a response to increased regulation, industry sources report that cadmium pigment use has been all but eliminated.

Toxicity and Environmental Impact
Animal studies have shown that cadmium pigments are potential carcinogens when inhaled, which is why they carry the warning, “do not spray apply”. They are not believed to be toxic by ingestion if they are of low solubility as determined by laboratory testing. Over the years, pigment manufacturers have produced cadmium pigments of progressively lower solubility of both the cadmium and selenium in efforts to increase safety. The solubility tests are designed to mimic the pH, temperature and agitation that would be experienced in the stomach. However, detractors from this theory correctly point out that there are other mechanisms at work in the body and that these analyses should not be considered entirely conclusive. Therefore, while use of low solubility cadmium pigments diminishes their toxicity, there is still reason to treat paints made with cadmium pigments with extra care and to seek alternatives.

In the industrial setting of the paint manufacturer, where inhalation of dry pigment is much more likely, the Occupational Safety and Health Administration (OSHA) regulates all cadmium compounds and has set stringent workplace exposure limits and hygiene requirements. OSHA’s permissible exposure limit for cadmium exposure through inhalation is 5 micrograms per cubic meter of air breathed. In an 8 hour workshift, approximately 9 cubic meters of air are breathed. Workers exposed to cadmium approaching this level are required to have periodic testing to determine their blood levels of the element.

There are also concerns regarding the long term environmental impact of cadmium in landfills. These are largely the result of the use of soluble cadmium compounds in battery manufacture and the proliferation of spent batteries in the waste stream. However, for the purposes of reducing the potential for cadmium compounds leaching out of landfills, cadmium from all sources is of concern to the agencies regulating waste disposal. Any cadmium-containing waste that leaches levels of the metal greater than 1 mg/liter in the Environmental Protection Agency (EPA) Toxicity Characteristic Leaching Procedure test method is considered hazardous waste. This is a rigorous acid solubility test which some cadmium pigmented artists paints will not pass. In recent years, numerous states have passed additional regulations designed to reduce cadmium entering the waste stream from the packaging and printing industries, regardless of solubility.

Periodically, bills are introduced in state legislation that would prohibit uses of cadmium in consumer products. In Minnesota, a bill to this effect was passed for ink, paint and dye products, but did contain an exemption for art materials. Similarly, in Europe, art materials enjoy an exemption from prohibitions of cadmium use in consumer products.

The result of increased regulation and concern over toxicity is that cadmium pigment use in the United States has declined about 75%, from approximately 2375 tons in 1987 to 550 tons in 1995. Of this, an industry representative estimated that approximately 5% to 7% is used for artists paint. The number of manufacturers of these pigments has also decreased significantly. While industry representatives believe the trend may be leveling somewhat, one cannot help but wonder if regulatory pressure will ultimately prevent the use of cadmium in artists paints, or otherwise result in supply problems due to the downsizing of the industry.

There is another perspective to the issue of the relative safety of cadmium pigments compared to organics. Due to the OSHA regulations, industrial exposure to cadmium pigments is extremely low. Cadmium entering the wastestream is much more closely controlled. Meanwhile, organic pigment use is treated much more casually with less stringent worker protection in terms of personal protective equipment and industrial hygiene. Those who play devil’s advocate wonder if these new organic pigments, which have been evaluated for toxicity less thoroughly by virtue of their newness and lack of long term epidemiological data, will remain untarnished as they come under closer scrutiny in the years to come.

Golden Artist Colors, Inc. will continue to try to make the best choices based on current knowledge, such as selecting cadmium pigments of the lowest solubility and searching for what are believed will be safest alternatives. Even so, we urge users to control their exposure to any artist material. Treat every material as if it could be chronically toxic. In all cases avoid ingestion, excessive skin contact, and if spraying or sanding, use a NIOSH approved respirator. Maintain a moderate level of general dilution ventilation. These are considered good chemical hygiene practices. In following them, unknown potential toxicity matters less, because if materials don’t enter the body, they can not be harmful.

Alternatives to Cadmium Pigments
It is apparent that we should not count on cadmium pigments being available forever. Golden Artist Colors, Inc. has undertaken years of research in an effort to identify and market suitable alternative pigments. Important characteristics include hue or color position, chroma or color saturation, opacity, indoor lightfastness, and tinting strength. Alternatives should also present distinct advantages over cadmium pigments in the areas of potential toxicity, environmental impact and exterior lightfastness. This is quite a list of objectives, and presents a difficult task, particularly in the yellow range.

However, with the introduction of the Pyrrole family of pigments in 1988, there appear to be good offsets, in terms of these identified criteria, for the orange to medium red range. Additional products utilizing this chemistry, currently under development by the industry, will extend this range into the darker reds. The pyrrole family of pigments is currently represented on the GOLDEN palette by three colors, Pyrrole Orange, Pyrrole Red Light, and Pyrrole Red. These are strong tinting, high chroma colors with excellent lightfastness.

Identifying suitable alternatives for the cadmium yellows has been a somewhat more difficult task. The Bismuth Vanadate family offers many of the attributes being sought, but concerns over the toxicity of the constituent heavy metals (bismuth and vanadium), seem to indicate they may offer little benefit over cadmium pigments. Instead, we found that a member of the arylide family of pigments seems to offer the best choice for the artist eschewing cadmium pigment. This pigment, PY 74, is the colorant in GOLDEN Hansa Yellow Opaque. It is of a hue between Cadmium Yellow Light and Cadmium Yellow Medium. Its relatively high opacity and excellent interior lightfastness are characteristics not normally encountered in this class of pigment. Exteriorly, its lightfastness is far superior to cadmium yellow and should also exceed the performance of Hansa Yellow Medium (PY 73) and Hansa Yellow Light (PY 3), the other members of this pigment family offered by GOLDEN. There are currently no environmental or toxicity issues associated with PY 74. The tinting strength of Hansa Yellow Opaque is also significantly higher than what might be expected from an arylide and is closer to that characteristic of a cadmium pigment. The arylide yellows are entirely organic in composition, containing no metals. While one pigment doesn’t provide a range of choice equal to that available in the current range of cadmium yellows, it is a starting point. Using it as the primary component of a mixing color will extend its attributes to other hue positions.

Although the properties of these new organic pigments are in many ways similar to cadmium colors, they are not identical in every respect. The biggest variation is how the colors mix to create new colors. Organics typically produce cleaner, less muddy mixtures. Other colors, such as the iron oxides, can be added if muddier colors are needed.

Once established, a pigment is rarely deemed entirely superfluous. Cadmium pigments will always have devotees, regardless of any disadvantages. An example of this persistence is the continued demand for true Alizarin Crimson, a pigment that fades badly, long after the introduction of the highly stable quinacridone family, from which a nearly identical match may be made. Another example is the continued demand for lead white, despite its toxicity, concerns about environmental impact and suitability of Titanium and Zinc White blends.

Long term availability of cadmium pigments may be determined by regulatory pressure or by reduced demand resulting from the increased use of new pigments.

It may likely be both.