Inorganic Yellow Pigments
By and large, inorganic pigments are usually made from a metal oxide or a mixed metal oxide. This is because inorganic pigments are sought for their covering power and opacity. Also, a pigment generally needs to be insoluble and non-reactive to the medium it’s incorporated into, so soluble and slightly soluble metal salts are ruled out for the most part.
Many yellow inorganic pigments are highly toxic, and proper care and preparations should be taken. There are safer alternatives, but eye protection, gloves, and a dust mask should be at least the minimum when handling any dry pigment powder.
Yellow Oxide and Ochre Pigments
By far the earliest-used pigments were earth pigments. These pigments are generally crumbly clays colored by different forms of iron oxide. Early hunter-gatherers used them for cave painting to make graphic depictions of their daily lives. Through the ages, they were used to paint homes and public buildings while also included in the artist’s pallet.
These pigments are lightfast and usually enhance the strength of the paint film regardless of what medium is used. Also, these oxide and ochre pigments exhibit relatively low toxicity. Those properties and their low cost helped maintain their importance even through the Industrial Revolution and into the present age.
It should be noted that yellow ochres and iron oxide pigment might frequently have harmful impurities like manganese or crystalline silica. Therefore, a dust mask or respiratory protection is recommended.
French chemist Louis Vauquelin discovered the element chromium in 1797. Within 20 years, lead chromate was being used as a paint pigment called chrome yellow. Lead chromate occurs naturally as a mineral called crocoite, but the mineral has never been used to make pigment. Instead, water solutions of lead nitrate and potassium chromate were mixed to deposit the insoluble lead chromate.
Chrome yellow can darken on exposure to industrial atmospheric pollution when hydrogen sulfide is present. Hydrogen sulfide can react with the lead to form black lead sulfide.
Chrome yellow is a pigment compound consisting of the toxic heavy metal lead as well as the highly toxic and carcinogenic hexavalent chromium ion chromate. Chrome yellow was replaced by cadmium yellow and orange blend to mitigate the hazards. Ultimately, modern organic monazo pigments replaced even the cadmium pigments due to environmental and health concerns.
Chrome yellow is a bold, deep, orange yellow that is mostly imitated in modern art paints by less hazardous substitutes. The traditional lead chromate pigment can sometimes be found wherever art conservation supplies are sold.
Although cadmium yellow was known as pigment in the middle of the 19th century, it did not get much use in paints due to the scarcity of cadmium metal. It wasn’t until a more modern and efficient industry increased the production of cadmium in the early 20th century, reducing its costs. Cadmium yellow, followed shortly later by orange and red, showed up on artist palette. These were bold and bright colors that revolutionized the art world. They are opaque and stable indoors, but they do deteriorate outdoors by chalking and fading.
In recent decades, there have been concerns not only about the health hazards of cadmium pigments but also their environmental effects. Cadmium is a highly toxic heavy metal in soluble form. Although cadmium yellows are generally insoluble, they still pose a significant inhalation hazard and as problematic solid waste. In many industries, cadmium pigments have been replaced by less hazardous organic yellow pigments.
Artists still are easily able to purchase both cadmium dry pigments as well as ready made paints. Despite the lower toxicity of the replacement organic pigment, some artists insist on using cadmium pigments because not only because of their hues and chroma but also because they are more opaque. Manufacturers have also been coating cadmium pigments to make them less soluble so the toxic metal cannot be leached out as easily. So, as long as artist take proper safety precautions such as not sanding cadmium paint coatings or spraying cadmium paints, and wearing proper safety gear, these pigments can be enjoyed for their beneficial properties.
Bismuth Vanadate Yellow
Bismuth vanadate is another yellow pigment that has both high chroma and high hiding power. First synthesized in the 1920s for pharmaceutical use, it became widely available as a pigment worldwide in the mid-1980s. It is a mixed metal oxide that is less toxic than lead chromate and cadmium yellow. Also, the depth of the yellow color can be controlled somewhat by the conditions of its precipitation. It is made by reacting a solution of bismuth nitrate with a soluble vanadate.