Azo colors

Description

A large group of synthetic dyestuffs containing one or more nitrogen double bond (azo) groups as its chromophore. Azo chromophores were first discovered in 1858 when Johann Peter Greiss discovered diazotization. The first azo dye, Aniline yellow was produced in 1861, followed by Bismarck brown in 1863. By the 1880s numerous other azo dyes, such as Congo red, para red and primulin red, were developed. Since that time, most modern dyestuffs have been derived from diazotized aromatic amines and hence are sometimes known as diazo dyes. The simplest azo dyes are yellow, but changing the number of chromophores or the backbone structure can produce red, violet, blue and even black dyes. Azo dyes are used as textile colorants, and well as in industrial paints, printing inks, varnishes, plastics, crayons and other products. In recent years, many high-performance azo pigments have been developed that meet the stringent lightfastness requirements required for artwork (Berrie and Lomax 1997). Modern regulations (such as REACH in the EU) have phased out dyes that release carcinogenic amines, replacing them with safer chemical structures.

Comparison of Key Historical Azo Dyes

Dye Name	Discovered	Key Property	Historical Significance	Common Use Today
Aniline Yellow	1861	High solubility but poor lightfastness.	The first commercialized azo dye.	Minor industrial marking.
Bismarck Brown	1863	One of the first widely used basic dyes.	Proven success in industrial-scale synthesis.	Biological staining, leather dyes, coloring fish bait.
Para Red	1880	"Ingrain" dye (formed inside the fiber)	First azo dye that didn't wash out of cotton	Limited (largely replaced)
Congo Red	1884	Direct dye (no mordant needed for cotton).	Revolutionized the textile industry for the masses.	pH indicator; amyloid fiber detection.
Tartrazine	1884	Vibrant yellow; high thermal stability.	Transitioned dyes from textiles to the food industry.	Food coloring (Yellow 5).
Prontosil	1932	Bio-activated (breaks down into sulfonamide).	First synthetic antibacterial/antibiotic drug.	Medical history (ancestor of sulfa drugs).

Use of Azo Dyes and Pigments in Artwork

Classification	First developed	Lightfastness	Heat stability	Other properties	Common uses	Azo Pigments used in traditional artists paints, primarily from Berrie and Lomax 1977.
Pyrazolones	1884	very good	to 150 C	High transparency and good heat resistance; sensitive to solvents and water.	Paints: architectural, artist Coloring: textiles, rubbers	CI 19140 (PY 100, AY 23, Tartrazine); CI 18965 (AY 17); CI 12705 (Reactive Yellow 145)
Naphthol Reds	1911	very good	to 160 C	Highly resistant to acids, alkalis, and soaps; good tinting strength and inexpensive; poor bleed resistance	Paints: architectural, automobile Coloring: plastics, paints, inks	PO38 (CI 12367); PR2 (CI 12310); PR3 (CI 12120, Toluidine Red) PR5 (CI 12409); PR7 (CI 12420); PR8 (CI 12335); PR9 (CI 12460); PR12 (CI 12385); PR14 (CI 12380); PR17 (CI 12390); PR18 (CI 12350); PR22 (CI 12315, Fast Red 1); PR23 (CI 12355); PR31 (CI 12360); PR112 (CI 12370); PR119 (CI 12469); PR146 (CI 12485); PR17O (CI 12475); PR187 (CI 12468); PR188 (CI 12467)
B-Naphthols	1895-1911	very good	to 150 C	Good chemical resistance but poor bleed resistance	Paints: architectural Coloring: plastics, rubbers, chalks, crayons, inks	PO2 (CI 12060); PRO5 (CI 12075, dinitroaniline orange); PRO17 (CI 15510); PR1 (CI 12070, Para Red); PR3 (CI 12120, Toluidine Red); PR4 (CI 12085, chlorinated Para Red); PR48 (CI 15865); PR49 (CI 15630); PR52 (CI 15860); PR53 (CI 15585); PR57 (CI 15850); PR60 (CI 16105)
Arylide (Hansa) Yellows	1900	very good	to 150 C	Good lightfastness; resistant to water, oil, acids and bases; but not bleed resistant	Paints: architectural, artist Coloring: chalks, crayons, inks	PO1 (CI 11725); PY1 (Hansa Yellow G; CI 11680); PY3 (Hansa Yellow light; CI 11710); PY4 (CI 11665); PY5 (CI 11660); PY9 (CI 11720); PY65 (CI 11740); PY73 (CI 11738, Hansa Yellow); PY74 (CI 11741, Hansa Brilliant Yellow 5GX); PY75 (CI 11770); PY97 (CI 11767); PY98 (CI 11727)
Diarylide Yellows and Oranges	1911	poor to good	to 150 C	Primarily used for printing inks, they have twice the tinting strength of the arylides with more bleed resistance	Paints: architectural, artist Coloring: plastics, rubbers, inks	PY12 (Benzidine Yellow AAA; CI 21090); PY13 (Permanent Yellow GR; CI 21110); PY14 (Benzidine Yellow AAOT; CI 21095); PY17 (Benzidine Yellow AAOA; CI 21105); PY55 (CI 21096); PY81 (CI 21127); PY83 (Permanent Yellow HR, CI 21108); PO14; PO15; PO16 (dianisidine orange)
Nickel-azo	1940	excellent	good	Expensive but excellent lightfastness, low blend and toxicity; often used in blends with blue to make green	Paints: artist, automobile Coloring: textiles	PG10 (CI 12775); PY150 (CI 12764); PY 151 (CI 12760); PY 153 (CI 77860)
Disazo dyes	1870	very good	to 180 C	Their high molecular increases their lightfastness and decreases their solubility.	Paints: automobile Coloring: plastics, textiles, inks	BO2 (Chrysoidine, CI11270); AR66 (CI 26905, Biebrich Scarlet); Dr28 (CI 22120 Congo Red)
Benzimidazolones	1960	excellent	>100 C	Outstanding bleed resistance, lightfastness and moderate heat resistance	Paints: artist, automobile Coloring: plastics, chalks, crayons	PBr25 (CI 12510); PO36 (CI 11780); PO60 (CI 11782); PO62 (CI 11775); PR171 (CI 12512); PR175 (CI 12513); PR176 (CI 12515); PY151 (CI 13980); PY153 (CI 48545); PY154 (CI 11781); PY175 (CI 11784)

Synonyms and Related Terms

diazo dyes; azo pigments; coal tar colors; ice colors; arylide dyes; Azofarbstoff (Deut.); colorante azoico (Esp.); colorants azoïques (Fr.); colorants azo (Fr.); colorante azoico (It.); corante azo (Port.)

See also Para red, Lithol red, Toluidine red, Tartrazine lake, Hansa pigments, Hansa red, Hansa yellow, Hansa orange

Risks

Some azo dyes are highly toxic and carcinogenic.

Resources and Citations

• A.Bafana, D.Sivanesan Saravana, T.Chakrabarti, "Azo dyes: past, present and the future" Environmental Reviews. 19(NA): p.350-371, 2011 link
• E.Yates, A.Yates, "Johann Peter Griess FRS (1829-88): Victorian brewer and synthetic dye chemist" Notes Rec R Soc Lond. 70(1):65-81, 2016 Link
• B.Berrie, S.Q.Lomax, "Azo Pigments: Their History, Synthesis, Properties and Use in Artists' Materials" in Studies in the History of Art, No.57, National Gallery of Art, Washington DC, 1997.
• Schweppe H, Practical Information for the Identification of Early Synthetic Dyes. 1987, Smithsonian Institution: Washington, DC. Yellow Book download
• Colorants Industry History at colorantshistory.org
• G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 284
• Ralph Mayer, A Dictionary of Art Terms and Techniques, Harper and Row Publishers, New York, 1969 (also 1945 printing)
• Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
• Hoechst Celanese Corporation, Dictionary of Fiber & Textile Technology (older version called Man-made Fiber and Textile Dictionary, 1965), Hoechst Celanese Corporation, Charlotte NC, 1990
• Van Nostrand's Scientific Encyclopedia, Douglas M. Considine (ed.), Van Nostrand Reinhold, New York, 1976
• Encyclopedia Britannica, http://www.britannica.com Comment: "azo dye" [Accessed April 1, 2002
• Meredith Dorner "Early Dye History And The Introduction of Synthetic Dyes Before The 1870s" -http://www.smith.edu/hsc/silk/Papers/meredith.html
• Thomas B. Brill, Light Its Interaction with Art and Antiquities, Plenum Press, New York City, 1980
• Wikipedia: Azo dye (Accessed Jan. 15, 2006 and May 2025)