In the first half of the semester, students in CHEM 550L learned to synthetically produce copper phthalocyanine (phthalo blue), indigo, Tyrian purple, Maya blue, Prussian blue and cyanotypes, and YInMn blue.
This resource provides background on those pigments and dyes and their synthesis, alongside photographs of lab experiments.
All descriptions, notes, and diagrams of chemical reactions were provided by Dr. Jade Fostvedt, unless otherwise noted. The pigments and dyes on view were produced by students in CHEM 550L.
Researched and developed by Grace White, paper conservator at the Ackland Art Museum
Copper Phthalocyanine (Phthalo Blue)
The pigment copper phthalocyanine (also called phthalocyanine blue, phthalo blue, and Monastral Blue) was first synthesized in 1927 by accident. The reaction of copper(I) cyanide and o-dibromobenzene produced colorless phthalonitrile and an intensely blue side product later identified as phthalo blue. In 1937, DuPont started producing the pigment phthalo blue in America under the trade name Monastral Blue.
Phthalo Blue Lab Notes
The reaction below is called the phthalonitrile process. Students heated phthalonitrile with a copper chloride salt at a high temperature. They added copper(II) chloride to hold the phthalonitrile molecules in position so that they can react to form a ring. Water inhibits the reaction, so they used a water-free solvent.
Indigo
The word “indigo” comes from the Latin word indicum, meaning “Indian,” as the natural dye was first exported to Europe from India. Indigo dye can be obtained from several different plants, including indigofera tinctoria, often called “true indigo,” Japanese indigo, Chinese indigo, Natal indigo, Guatemalan indigo, woad, and the American native species indigofera caroliniana.
Large-scale indigo plantation farming was introduced to the American South in the 1700s. Enslaved laborers enabled indigo farming to dominate in North Carolina, South Carolina, and Georgia, with indigo accounting for more than onethird of the value of American exports. Synthetic indigo was first produced in 1882.
Indigo Lab Notes
Students synthesized indigo using the Baeyer-Drewson reaction, shown below. The reaction combines two equivalents of 2-nitrobenzaldehyde with two equivalents of acetone (as in nail polish remover) to form indigo. Students then used the indigo they synthesized to dye fabric using a vat dyeing procedure.
From Indigo to Tyrian Purple
Tyrian purple is a famous purple dye that is derived from marine snail shells. The Tyrian purple molecule has a very similar structure to indigo, with the addition of two bromine atoms. Students in CHEM 550L synthesized Tyrian purple using a similar method as employed for indigo. Comparison of the two dyes allowed students to investigate how adding different atoms to a structure changes the color.
From Indigo to Maya Blue
Maya blue is a pigment used by ancient Mayan artists; archeological investigations suggest that this pigment was used to paint murals, color objects, and as a body paint.
To make Maya blue, first the indigo molecule is isolated from a species of indigo native to Mexico and South America (Indigofera suffruticosa). Then, the indigo dye is mixed with a clay found in the Yucatán peninsula, called palygorskite. The clay has a unique porous structure that allows the indigo molecule to become trapped within the clay, preventing the dye from being washed away by water. Incorporation into the clay results in a pigment that has a lighter color than indigo on its own.
Atomic structure of palygorskite clay
Prussian Blue
Prussian blue was first synthesized (by accident!) in 1704 in Berlin, Germany. It has an intense dark blue color and is used extensively as a pigment in paints and inks.
Prussian blue is the pigment used in cyanotype printing, a photographic printing process discovered by Sir John Herschel in 1842. Architectural blueprints, for example, are cyanotypes.
Cyanotype Process
Ferric ammonium citrate + Potassium ferricyanide
Prussian Blue
Prussian Blue Lab Notes
In this lab, students first made cyanotypes. Students then synthesized a sample of Prussian blue by reacting ferric chloride, FeCl3, with potassium ferrocyanide, [K]4[Fe(CN)6], as depicted below.
YInMn Blue
YInMn Blue was discovered in 2009 at the University of Oregon. It is both stable and nontoxic, distinguishing it from other blue pigments. Since its discovery, YInMn blue has been used as both an industrial and artist pigment. It has been called a "perfect blue,” for the absence of red or green tones, its ability to reflect infrared light (heat), and its stability under ultraviolet light illumination.
YInMn Blue Lab Notes
In this lab, students synthesized various metal oxides of the formula YIn(1-x)MnxO3, where the product color depends on the ratio of indium and manganese oxides added. The reaction equation, as well as the crystal structure of YInMn Blue, are depicted below.
