TOP 40 PIGMENT  Phthalocyanine blue PB15 in its various shades (PB15:1 and PB15:6 are middle blue or reddish shades; PB15:3 is the greenish shade) is the workhorse industrial blue colorant: a lightfast, transparent, strongly staining, very dark valued, moderately intense blue pigment, offered by over 70 pigment manufacturers worldwide for inks, paints, plastics, automotive finishes, rubber, textiles and cosmetics, as well as artists' paints (where it is often nicknamed phthalo or thalo blue, as the "ph" is not pronounced).

The ASTM (1999) rates the lightfastness in watercolors of PB15 as "very good" (II), though it has excellent lightfastness in manufacturer and my 2004 tests across all the brands listed above. Pigment processing alters the paint handling characteristics (lightfastness and color intensity vary with the pigment particle size), and PB15:3 can even be formulated to flocculate in imitation of manganese blue (PB33).

In watercolors the blue phthalocyanine pigments undergo a very large drying shift, lightening (by 26% in the green shade, 46% in the red shade) and losing 20% or more in saturation.

PB15 differs significantly across manufacturers, primarily in hue (as suggested by the chart above), but also in tinting strength, lightness and hue shift. (It typically makes a large hue shift toward green from masstone to undertone, which means the hue positions in the chart are approximate.) Because of their dark color, the phthalocyanines reach maximum chroma when moderately diluted. The green shades of phthalo blue are (along with cerulean blue) very close to the psychological unique blue, as explained in the section on color vision; the warmer shades make an excellent choice for color point 8 of the color wheel. The tinting strength of phthalo blue is typically high, but varies by manufacturer. The best mixing complements for phthalo blue, depending on hue, are venetian red (PR101) or cadmium orange (PO20) (red shade) and venetian red (PR101) or perinone orange (PO43) (green shade). The average CIECAM J,a,b values for phthalo blue (PB15:3) are: 27, -31, -48, with chroma of 57 (estimated hue purity of 59) and a hue angle of 237. For phthalo blue RS (PB15:1) the average values are: 24, -23, -49, with chroma of 54 (estimated hue purity of 56) and a hue angle of 245; for phthalo blue GS (PB15:3) they are: 28, -36, -48, with chroma of 60 (estimated hue purity of 63) and a hue angle of 233.

M. Graham phthalo blue and Daniel Smith phthalo blue are both located toward the red end of this distribution. Either one makes an excellent single phthalo blue: dark valued, with high tinting strength, good saturation, and some of the largest hue shifts among phthalos listed here, they apply evenly at full strength or in tints. The Daniel Smith is slightly lighter valued, with subtle texture but less movement in wet applications. Blockx blockx blue dissolves less evenly and is inert wet in wet; however, it is the dullest and darkest phthalo tested here (the Rowney Artists RS is much more saturated but with the same hue). At the extreme of greenish hues, Utrecht phthalo blue is lighter (less concentrated) and will not make strong darks, but is a sweet, bright color and active wet in wet. — Phthalo blues are now frequently offered as a warm/cool (red hue/green hue) pair (by Winsor & Newton, Daniel Smith, MaimeriBlu, Rembrandt, Rowney Artists, Schmincke). The most saturated and widely spaced of these phthalo twins are Winsor & Newton winsor blue RS and winsor blue GS. These paints bracket the hues of almost all other paints listed here (only the Utrecht is greener than the winsor blue GS); the red shade is darker valued than the green, and the GS makes a very good single phthalo choice, contrasting nicely to the reddish hue of cobalt blues or ultramarine blue. The Schmincke and Rowney Artists paints are spaced roughly half as far apart in the CIELAB color space. The MaimeriBlu and Daniel Smith pair of paints are even closer together. All these brands have good tinting strength and are moderately active in wet applications, but typically the RS tends to blotch if applied in long brushstrokes wet on dry (the pigment particles are apparently coarser). Finally, phthalo blue is sometimes mixed with phthalocyanine green (usually PG7) to produce turquoise convenience mixtures. MaimeriBlu green blue is more saturated and slightly greener than the Daniel Smith phthalo turquoise, which is darker and more staining.

Cobalt or ultramarine blues tend to be picked more often in palettes because they stain less harshly, and offer more interesting texture. But phthalo blue's tinting strength and dark masstone color make it a good choice as the foundation tint over which other nonstaining paints can be glazed and then selectively lifted or blotted away. It is a beautiful sky color in dilute washes. It mixes well with a wide range of paints, including the yellow cadmiums, though it can be blotchy on highly sized paper and unforgiving when used on absorbent paper. Iron blue (PB27) is less intense but produces very moody darks, while ultramarine mixed with cobalt turquoise light (PG50) produces an equivalent hue with a distinctive pigment texture. See also the section on phthalocyanine pigments.

TOP 40 PIGMENT  Phthalocyanine turquoise PB16 is a lightfast, semitransparent, heavily staining, moderately dark to very dark valued, moderately dull green blue pigment, available from 3 pigment manufacturers worldwide. In watercolors, PB16 undergoes a very large drying shift, lightening by 20% and losing almost 30% saturation. Like other phthalos, its chroma greatly increases as it is diluted, and the color can be radiant in tints. Even so, it is the darkest of all phthalocyanine paints, an interesting alternative to blue violet paints as a shadow color. The tinting strength of phthalo turquoise is typically high, but varies by manufacturer. The best mixing complements for phthalo turquoise are perinone orange (PO43) or cadmium scarlet (PR108). The average CIECAM J,a,b values for phthalo turquoise (PB16) are: 23, -36, -27, with chroma of 44 (estimated hue purity of 52) and a hue angle of 217.

MaimeriBlu turquoise green is the most chromatic, lightest valued, least staining and most transparent; it also was the most lightfast in my tests. The Winsor & Newton paint is quite blue in masstone, indistinguishable from a green PB15:3, but undergoes a very large hue shift in tints. Utrecht appears to use the same pigment, but the paint has a lower tinting strength, bronzes when applied full strength, and fades slightly in tints. Holbein marine blue is a darker color that dilutes into lovely tints, and is moderately active on wet paper. The Old Holland caribbean blue is the dullest of all. The pigment available from Robert Doak is also worth investigating, though it stains paper like sin.

In 1998 I wrote that PB16 was "not widely available in watercolor paints, but is an attractive pigment". Now that Winsor & Newton has joined the club, Daniel Smith is sure to follow. The hue is readily mixed from a good phthalo green BS (PG7) and a phthalo blue GS; or try cobalt teal blue (PG50) for the "green" paint, which gives a lighter valued and satin textured color. You can also mix phthalo turquoise with ultramarine blue (PB29) or quinacridone violet (PV19) for some really celestial dark blues and blue violets. See also the section on phthalocyanine pigments.

 Phthalocyanine cyan PB17 is a lightfast, semitransparent, staining, dark valued, intense green blue pigment, available from only 2 pigment manufacturers worldwide (one of them in China). In watercolors, PB17 undergoes a moderately large drying shift, lightening by 20% and losing saturation. The best mixing complements for phthalo cyan are cadmium scarlet (PR108) or quinacridone maroon (PR206). The average CIECAM J,a,b values for phthalo cyan (PB17) were: 35, -50, -46, with chroma of 68 (estimated hue purity of 69) and a hue angle of 223.

Holbein peacock blue, now discontinued, was the only commercial source for this pigment in watercolors; however it is still available as Holbein Irodori "Antique Turquoise". (Note that the Irodori formulations are described as "delicate hues" that "granulate freely" and are "more opaque".) PB17 is a very pretty blue turquoise color, inert wet in wet, with a bright undertone. Slightly less lightfast than the other phthalocyanines, it is just as transparent and slightly more chromatic; however, the Holbein formulation had a slightly lower tinting strength than most phthalo blues. Its bright cyan color is quite close to the artist's "primary" cyan at color point 9 on the color wheel.

Substitutions. Depending on the other choices for blue, and the mixtures that those choices imply, PB17 is an inessential pigment. I prefer the greater value range, mixing strength and lightfastness of a green shade of phthalo blue (PB15:3) for this hue. See also the section on phthalocyanine pigments.

TOP 40 PIGMENT  Iron blue PB27 is a fugitive to very lightfast, semitransparent, staining, very dark valued, moderately dull blue pigment, now available from only a handful of pigment manufacturers worldwide, mostly for printing inks and cosmetics.

PB27 can achieve a beautifully saturated, very dark color in some preparations, but when used in watercolors its finished color is usually muted, greenish and moody. The masstone color is close to a reddish phthalo blue; it shifts very noticeably toward green in tints, and presents a similar large drying shift (lightening by 68% and dropping 20% in chroma), making this one of the most dynamic pigments available. The pigment particles are extremely fine, but the pigment usually agglomerates or clumps, depending on how it is manufactured, to create a stringy or flaked texture that cannot be milled out and that appears in the M. Graham and Daniel Smith paints as tiny, dark flecks when the paint is applied. The best mixing complements for iron blue are venetian red (PR101) or perinone orange (PO43). The average CIECAM J,a,b values for iron [prussian] blue (PB27) are: 19, -17, -36, with chroma of 40 (estimated hue purity of 45) and a hue angle of 245; for antwerp blue (PB27) they are: 35, -29, -38, with chroma of 48 (estimated hue purity of 47) and a hue angle of 233.

One of the first synthetic inorganic pigments, iron blue was discovered by Heinrich Diesbach in 1704 and made available in artist's colors in the early 1730's. Valued for its high tinting strength and pure blue hue, PB27 was hugely popular from the 18th to the 20th centuries until displaced in the 1970's by phthalo blue. Historical and current uses include inks, housepaints, wallpaper, fabric dyeing, histological stains and blueprints. There are two chemical pathways for manufacturing PB27 that can be applied to a variety of raw materials to produce the same pigment molecule, but the color, crystal form and particle size of the pigment can be manipulated in many ways during or after manufacture. (There is even a prussian brown created by calcining or roasting the finished pigment.) Manufacturing impurities were once difficult to remove from the finished product, and historically the pigment was mixed with other colorants to create a greater color variety, especially for various blues and convenience greens such as hooker's green and prussian green. As a result, a large number of proprietary or geographic names (prussian blue, berlin blue, erlangen blue, hamburg blue, haarlem blue, oriental blue, persian blue, paris blue, milori blue, gas blue, saxon blue, cyanine blue, leitch's blue, potash blue, turnbull's blue, etc.) have accumulated around PB27 to distinguish among the many manufacturers, manufacturing methods, grades of pigment and mixtures with other pigments or extenders. The generic name iron blue has replaced these picturesque nuances, though bronze blue denotes any reddish grade used in printing inks, including the highest quality pigment known as chinese blue. See also the section on iron pigments.

The ASTM (1999) rates the lightfastness of PB27 in watercolors as "excellent" (I), but my lightfastness tests showed that this pigment is unusually variable both within and across brands. Many brands faded very slightly in masstone (1% or 2% of lightness) after one to two weeks of sunlight exposure, while other brands faded substantially in either masstone or tint or both; but after this early color adjustment most remained stable over the remaining test period. (The standard lightfastness test procedure requires measurement of the total fading at the end of the exposure period, so the pigment does better in longer tests.)

iron blue lightfastness samples (2004)

after 800+ hours of sunlight exposure: (top, left to right) Utrecht, M. Graham, Rembrandt, Schmincke, Holbein, MaimeriBlu; (bottom, left to right) Rowney Artists, DaVinci, Van Gogh, Daniel Smith, Winsor & Newton, Winsor & Newton antwerp blue

The fading was most obvious in paints labeled antwerp blue, historically the name (with mineral blue or brunswick blue) applied to mixtures of iron blue with a white pigment or extender (such as alumina, barium sulfate, zinc oxide or starch). In contemporary watercolors, iron blue commonly fades when mixed with any white pigment or extender, including titanium oxide. (The most permanent and apparently purest brands are placed at the top of the list above.) PB27 also can fade on contact with alkalis such as calcium carbonate, ammonia or bleach that can be used in paper manufacture ("buffered" watercolor papers may be slightly alkalinic), but in my experience the alkali must be fairly concentrated to affect the color in a good quality pigment. It cannot be used in fresco or casein paints.

PB27 is completely nontoxic and nonpolluting; it has even been used as an oral antidote to heavy metal poisoning and as a soil treatment (to increase iron) in agriculture. It can produce cyanide gas if heated or burned, and it has been known to ignite during grinding.

Iron blue is highly variable across manufacturers, both in texture and in lightfastness. M. Graham prussian blue is one of the greenest shades, slightly lighter valued than the rest and very active in wet applications; it has a noticeable pigment texture or flaking with good lightfastness. Daniel Smith prussian blue is by contrast slightly redder, darker and more saturated in masstone, with an exquisite subtle texture and good lightfastness. Winsor & Newton prussian blue is made from an especially fine textured pigment: it is the most saturated, provides good darks and handles well in all applications (it is relatively less active wet in wet but backruns readily); but unfortunately it faded slightly in masstone, lightening by about 2% in one week. The Rembrandt prussian blue has a nearly identical color appearance, but is more lightfast. The Rowney Artists paint is darker valued and even redder in hue, but without the texture. The Utrecht prussian blue is lighter valued and is one of the most saturated iron blue paints, but in my lightfastness tests it faded noticeably within a few days. (The remaining prussian blues are similarly dark, moderately dull and untextured; there is little to choose among them. Not listed above, the VanGogh prussian blue also had excellent lightfastness.) All these paints have a greener undertone. Finally, both Winsor & Newton antwerp blue and Art Spectrum antwerp blue are much lighter, greener and slightly more saturated versions of prussian blue mixed with alumina: both are fugitive. Daniel Smith's prussian green imitates a dull, dark turquoise or "sea green" convenience mixture with cadmium yellow introduced in the 19th century and rarely used since then.

CAUTION. The variability in PB27 across paint manufacturers suggests it should be routinely put through a lightfastness test, and especially when marketed as antwerp blue. Tiny, dark flecks and a visible but subtle texture seem to identify the more permanent pigments. You may also want to test the dried paint with household alkalis such as ammonia.

TOP 40 PIGMENT  Cobalt blue PB28 is a very lightfast, semitransparent, moderately staining, dark valued, moderately intense blue pigment, available from 12 pigment manufacturers worldwide. The ASTM (1999) rates its lightfastness in watercolors as "excellent" (I), and all manufacturer and independent tests agree. In my lightfastness tests I found a slight whitening or clouding of the masstone color in several brands (right), which may have been due to increased opacity in a paint extender or oxidation of the smallest pigment particles. In watercolors, PB28 undergoes a moderately large drying shift, lightening and losing saturation. The best mixing complements for cobalt blue are raw umber (PBr7) or benzimida orange (PO62). The average CIECAM J,a,b values for cobalt blue (PB28) are: 34, -28, -60, with chroma of 66 (estimated hue purity of 68) and a hue angle of 245.

Cobalt pigments are the "cadmiums of cool," creating hues across the cool part of the color circle from violet through blue to green, in the same way that cadmium hues extend across the warm colors from yellow through orange to red. This is because cobalt oxide can crystallize with several other common metals (aluminum, titanium, chromium, nickel, zinc, and tin) to produce a broad range of pigment colors that vary in both hue and lightness. The color becomes lighter and less saturated as the hue changes from blue violet to green. A pure cobalt oxide has a hue close to middle blue with a beautiful range of textures, from homogenous to flocculating, that vary with particle size and dilution. It is one of the most expensive pigments, and is sometimes imitated by a green shade of ultramarine blue (PB29), or ultramarine blue altered with phthalocyanine blue (PB15), an ingredient that increases the paint's staining effect on paper.

Available cobalt blue pigments are fairly consistent across manufacturers, with some variation in texture, chroma, value, and hue shift. M. Graham cobalt blue is a lovely powdery, dark blue, with a redder and more intense color than most other brands, but still a nice contrast to ultramarine blue. It is opaque when applied full strength but will stand considerable dilution, creating beautifully delicate wash textures. Daniel Smith cobalt blue is apparently a less concentrated preparation of a similar middle blue pigment, making it more transparent but less intense. Winsor & Newton cobalt blue is quite a bit more textured wet in wet and lighter valued, but it is the only completely transparent and also the least staining cobalt I've tried; the hue is the greenest and least saturated of any brand, which makes an effective contrast with ultramarine blue (PB29). The Rembrandt and Rowney Artists cobalt blues are darker valued and lean toward green, and for that reason are also less saturated; both also stain aggressively, perhaps due to the presence of a phthalocyanine pigment. MaimeriBlu's two cobalt blues are very similar to each other in hue and texture, and relatively opaque; the "light" shade closely resembles the Daniel Smith paint. The Holbein and Utrecht cobalt blues are relatively weak (containing a higher proportion of vehicle), but brush out to satisfying colors. Blockx cyanine blue imitates with phthalo blue the original cyanine blue formulation (cobalt blue mixed with prussian blue).

Cobalt blue is today often displaced from the palette by ultramarine blue (PB29) or phthalo blue (PB15), which have very different textural and handling characteristics but are less expensive. The color and texture can be approximated by ultramarine (PB29) mixed with a small amount of phthalo blue (PB15:3). But pure cobalt blue is unique: versatile in mixtures with a beautiful color that will endure forever, even in the thinnest wash, and a natural texture that accents the finish of any fine paper. See also the section on cobalt pigments.

lightfastness test samples
unexposed (left); exposed 800+ hours (right)

Rowney coeruleum blue, cobalt blue, ultramarine violet

TOP 40 PIGMENT  Ultramarine blue PB29 is a very lightfast, semitransparent, staining, very dark valued, intense violet blue pigment, available from about 20 pigment manufacturers worldwide (mostly for coloring cosmetics, paints and plastics). The ASTM (1999) rates its lightfastness in watercolors as "excellent" (I), but in some formulations the color can fade if exposed to mild acids (vinegar, lemon juice, urban air pollution). In watercolors, PB29 undergoes a very large drying shift, lightening by almost 30% and dropping almost 20% in chroma. PB29 comes in a range of shades, contrasted as a red (reddish blue) shade and a somewhat less expensive green shade. "French ultramarine" is conventionally the darker and redder shade, the ideal choice for color point 7 of the color wheel. The best mixing complements for ultramarine blue are raw umber (PBr7), benzimidazolone orange (PO62) or quinacridone gold (PO48); unique and beautiful mixtures, with very dark near neturals and dramatic color variety and wash textures are possible with burnt sienna (PBr7) or transparent red iron oxide (PR101). The average CIECAM J,a,b values for ultramarine blue (PB29) are: 21, -19, -68, with chroma of 70 (estimated hue purity of 73) and a hue angle of 254.

Ultramarine blue is probably included in artist's palettes more often than any other blue, the modern replacement and color match for the historical pigment lapis lazuli that appears in the most precious medieval art. (It's a triumph of modern chemistry that even the cheapest student paint box today contains the same pigment that medieval artists bought at many times its weight in gold.) And ultramarine is perhaps the most beautiful of all blue pigments: the French painter Yves Klein was famous for large canvases painted entirely in a powdery, intense shade of ultramarine blue, produced through a patented pigmenting technique. The pigment particles are soft and readily clump into agglomerates; this causes the characteristic ultramarine flocculating (clumping) texture that is especially attractive in washes and color mixtures. Paint manufacturers usually reduce the pigment clumps through extensive milling, which requires a dispersant to prevent caking; the dispersant causes many commercial ultramarine watercolors to diffuse aggressively wet in wet. The tinting strength of ultramarine is somewhat weak, especially in the reddish violet forms (see PV15).

PB29 is somewhat variable across manufacturers in hue, saturation, value, texture and transparency. The M. Graham, Daniel Smith, Rowney Artists and DaVinci french ultramarine blues are all very saturated and reddish, with a dark value that is not too dark to let the color glow, and that holds the rich hue in tints; the Rowney Artists permanent blue is a lighter valued and greener shade. The two Daniel Smith ultramarines are nearly identical in masstone hue and texture, but diverge in tints; the "french ultramarine" is slightly lighter and greener hued. These are all among the "smooth" or nonflocculating ultramarines, nearly transparent in washes or thin glazes. Winsor & Newton's pair of ultramarines are slightly lighter valued, greener in hue and more transparent than other brands, and produce some of the most pronounced (and lovely) wash pigment textures. The Holbein ultramarine deep and Blockx ultramarine deep also flocculate very nicely; both are as dark and intense as the ultramarines listed above, though the Blockx blackens in masstone. Some brands offer a "deep" ultramarine that is both darker and redder than the "light": The MaimeriBlu and Utrecht ultramarine blue paints are good quality; the hue difference between the Utrecht paints is the widest of any brand. The Schmincke ultramarine finest is also a greenish shade. Finally, the M. Graham ultramarine violet (PV15) is ultramarine blue shifted a small amount toward violet, but chemically the pigment is still an ultramarine blue (see the discussion under PV15).

A very saturated blue violet, ultramarine mixes vibrant and moderately lightfast violets with magentas such as quinacridone magenta (PR122) or quinacridone rose (PV19). In almost any palette ultramarine is an invaluable red blue. If ultramarine is the only blue you use, then one of the middle shades, particularly by Winsor & Newton, Daniel Smith or Utrecht, may be a more effective choice. See also the section on sulfur pigments.

 Manganese blue PB33 is a very lightfast, semiopaque, lightly staining, heavily granulating, moderately dark valued, moderately intense green blue pigment; also known as "cement blue" due to its use as a masonry colorant. The compound was first described in 1869 but not patented as a pigment until 1935. It was produced in Germany until around 1990, when it became cost prohibitive due to environmental regulations. The ASTM (1999) rates its lightfastness in watercolors as "excellent" (I). In watercolors, PB33 undergoes a very small drying shift. The average CIECAM J,a,b values for manganese blue (PB33) are: 46, -49, -45, with chroma of 66 (estimated hue purity of 65) and a hue angle of 223.

This crystalline synthetic inorganic pigment, a near perfect cyan hue, imparts a lyrically coarse texture even after extensive milling. Though never a popular paint, I feel this is of the loveliest blue pigments ever used in watercolors: it imparts a unique poetry to sky, water or landscape greens when used in diluted mixtures that put its granulation on display. Paint manufacturers add sufficient vehicle to ease the milling process and improve the flow of the paint, which typically causes the coarse pigment particles to separate from the vehicle in the tube. The weak, gooey texture of the diluted paint is difficult to apply evenly as a wash because the pigment immediately settles to the paper, although it is easily adjusted by rewetting the paint after it has dried.

Manganese blue is somewhat variable across manufacturers, primarily in saturation and pigment texture. Blockx manganese blue, now discontinued, was somewhat darker than the conventional manganese hue but with a beautiful deep hue and robust granulation, the best available choice. Holbein manganese blue has also been discontinued (and retail inventory has apparently been exhausted): it was moderately granular (and therefore easier to handle) and the most intense of the paints tested here, closest of all to the traditional manganese hue (as imitated by the typical "manganese blue hue"). The Old Holland is lighter valued and lackluster, and in masstone took on a greenish cast after long sunlight exposure; there is also an Old Holland manganese blue deep, which is a similar low grade pigment and prone to excessive vehicle separation. The Lukas paint is the lightest valued, least granulating and least saturated of all the brands, with a slight whitish opacity that suggests additives have been used. See also the section on manganese pigments.

Substitutions. Most paint brands offer a "manganese blue hue" made from phthalocyanine blue. The best substitute paints are Holbein's peacock blue (PB17, which has a nearly identical color but lacks the granulation), or the green shade phthalocyanine blue from Utrecht, Winsor & Newton, Rowney Artists or Rembrandt (PB15:3).

ALERT: Production of barium manganate ceased worldwide in the early 1970's and the pigment is no longer generally available in artist's materials. As of April 2006 there was still remnant inventory of Blockx manganese blue available in retail supplies (Jerry's Artarama and Art Suppy Warehouse), but this will shortly disappear; and Lukas still offered the pigment, apparently from their own pigment stockpiles or a niche pigment manufacturer. I don't feel the pricey, dingy Old Holland product is worth using.

TOP 40 PIGMENT See the comments below on this group of cobalt blues (ordered above by hue angle, from red to green). There is currently (2001) only one registered manufacturer of PB35 worldwide (Johnson Matthey, UK), but the range in pigment qualities in available watercolors suggests other suppliers are available. Coeruleum (pronounced "seruleum") is named after the original cerulean blue, first offered as an artist's color by Rowney in 1860. The Rowney Artists paint whitened in masstone, becoming a more pastel hue after a few weeks of sunlight exposure. The color is usually somewhat dull but the warm shades (with a hue angle around 245) are close to the psychological unique blue, as discussed in the section on color vision.

TOP 40 PIGMENT  The many shades of cobalt tin oxide (PB35) or cobalt chromium oxide (PB36), named cerulean blue, cerulean blue GS, cobalt turquoise or cobalt green deep, are very lightfast, semiopaque, moderately staining, granulating, dark valued, moderately dull to moderately intense blue to green blue pigments. PB36 is available from 9 pigment manufacturers worldwide (primarily as a colorant for ceramics, cement and industrial paints). The ASTM (1999) rates the lightfastness of these pigments in watercolors as "excellent" (I); manufacturer and my own tests agree. In watercolors, PB35 and PB36 show a very small (cerulean hues) to moderate (turquoise hues) drying shift, not lightening at all but losing from 5% to 20% in saturation.

The pigments lumped under the color index names PB35 and PB36 are highly variable across manufacturers in hue, value and saturation, as shown in the diagram below (manufacturer names are keyed by letters).

color variation in cobalt blue/turquoise paints

The span of hues ranges from the warm, moderately saturated M. Graham cerulean blue to the cool, dull Daniel Smith cobalt turquoise — another instance of the poor relationship between the color index name and the color appearance of pigments. (Hilary Page's quirk of adding "G" or "R" to the color index name has no sanction from either the Colour Index International or the paint manufacturers.) Note that the saturation and transparency of these pigments declines steadily as the hue shifts toward green: this is caused by the increasing proportion of chromium in the cobalt crystal. The paints above, ordered by hue angle (from red to green) fall into two main color categories:

• CERULEAN BLUE. The span of colors here is very broad. For this reason, some paint brands offer two shades of cerulean blue: the green shades are often darker valued (suggesting increased pigment load), and in all cobalt blues the color typically gets duller (less saturated) as the hue shifts toward green. A major consideration in the choice of a cerulean paint is its handling in washes, since it is often used for skies or other large, even color areas. The best paint from this point of view is perhaps Winsor & Newton cerulean blue, which gives beautifully flocculating, satiny wash textures, though at the expense of color intensity; its relatively subdued texture also makes it a better mixer with other paints. M. Graham cerulean blue is a mid valued, lovely muted blue with a hint of red; its assertive texture needs careful handling in a wash, but can produce dramatic textures or subtle flocculation (especially if the paint solution is first decanted), and it gives a radiant drama to skies. Rowney Artists coeruleum is significantly darker with coarser pigment grains. The Holbein paint is the most intense cerulean available, more granulating and less staining than any other brand. Rembrandt cerulean blue is a finely granulating, average cerulean hue, dark valued with sutble texture and good saturation, a very pretty color. MaimeriBlu cerulean blue is very dark in masstone, looking almost like a phthalo blue; it is much more attractive in tints. — At the "green" end of the cerulean color range, the Winsor & Newton cerulean blue and Daniel Smith cerulean blue are both dull and semitransparent; the Winsor & Newton is exactly a dull cyan hue, the greenest of the cerulean paints listed here. The two Utrecht paints have average saturation and are contrasted more on value than hue, which makes them a less useful pair (however, in 2001 Utrecht adopted a new GS pigment, not tested here); both paints leave a streaky, spotty wash texture. Rowney Artists has adopted an idiosyncratic labeling that only mucks things up: their "coeruleum blue" is the pigment PB35, a light valued, dull cerulean near the middle of the hue range; their "cobalt turquoise" paints are opaque, middle to greenish shades of cerulean (the hue of the "turquoise" RS is the same as their coeruleum!); and their "cobalt green deep" is what everybody else calls a cobalt turquoise. All the Rowney paints are also the darkest and dullest of the paints listed here. (In all, Rowney Artists offers six cobalt blue paints: the obvious question is, why?) Finally, Daniel Smith cerulean blue GS is an interesting color situated exactly between the clusters of "cerulean" and "turquoise" paints. The tinting strength of cerulean blue is weak. The best mixing complements for cerulean blue (depending on hue) are venetian red (PR101), burnt sienna or burnt umber (PBr7). The average CIECAM J,a,b values for cerulean blue (PB36) are: 37, -36, -45, with chroma of 58 (estimated hue purity of 57) and a hue angle of 231; for cerulean blue GS (PB36) are: 35, -39, -34, with chroma of 52 (estimated hue purity of 53) and a hue angle of 221.

• TURQUOISE BLUE. This is commonly a rather dull shade of dark green blue; phthalocyanine turquoise (PB16) is darker but more saturated. The color of PB36 brightens in tints, however, so (as with any dark valued or apparently dull paint) be sure you evaluate these paints across the complete value range, from full strength to tints. Among the cobalt turquoises, Winsor & Newton cobalt turquoise is slightly lighter and more saturated than the Daniel Smith, and less active in wet applications. Continuing with the Rowney Artists nonstandard naming choices for cobalt pigments, the Rowney Artists cobalt green deep is actually a cobalt turquoise, more concentrated (opaque) and darker valued than the other brands.

Since 2007 some paint lines (DaVinci, M. Graham, Grumbacher) have introduced a cobalt magnesium oxide (PG36) with a much much lighter and more saturated green blue color than cobalt turquoise showed previously; cobalt titanium oxide (PG50) is the same lovely hue, but is both more saturated and lighter valued. The DaVinci cobalt turquoise ("DV" in the paint color diagram, above) has a lightness, hue and small hue shift almost indistinguishable from the usual cobalt teal blue (PG50); the M. Graham paint appears to use the same pigment.

Best among many mixing complements for cobalt turquoise are quinacridone maroon (PR206), pyrrole orange (PO73), and most brands of cadmium red or cadmium red deep (PR108). The average CIECAM J,a,b values for cobalt turquoise (PB36) are: 39, -45, -17, with chroma of 48 (estimated hue purity of 49) and a hue angle of 201.

COMMENTS. The greenish blue and turquoise part of the color range (which includes phthalocyanine cyan, PB16, and cobalt teal blue PG50) has a peculiar status within the family of cool colors, much like red orange pigments on the warm side of the color wheel. Like orange (a mixture of red and yellow), turquoise is the mixture of two basic hues (blue and green); like orange, it is not anyone's favorite color, not a color that works well with other colors and not a color popular in clothing or interior decor; and as with burnt sienna (a dull red orange), cobalt turquoise, or phthalo turquoise PB16) (a dull blue green) is useful to mute the hue of other paints, or to adjust the color temperature of related blues or greens. This makes the cobalt cerulean and turquoise paints in many respects the "earth colors" on the cool side of the palette, providing texture, color stability, and muting effect to the brighter and more strongly tinting synthetic organic pigments. You should evaluate them from that point of view, and not just on their unmixed, full strength color appearance.

The cobalt cerulean and turquoise pigments are a definite preference among some artists, who rely on them to temper warm mixtures and create subtly textured pale blue washes (cerulean skies really are unique). The hue, value and texture of these pigments are highly variable across manufacturers (depending on the milling and the exact proportions of chrome, tin or aluminum in the pigment), as is apparent transparency (from the nearly transparent Winsor & Newton cobalt turquoise to the opaque M. Graham cerulean blue); but hue, texture and transparency all change as the paints are diluted, so evaluate them across a wide range of concentrations and mixtures. Cerulean blue is an excellent palette complement to ultramarine blue. (I find that cobalt blue PB28 is too close to the hue and value of ultramarine to provide distinctive mixing effects; but explore the variety of color choices in artists palettes that include cerulean blue.) If PB35/PB36 appeals to you, it is worth your time to sample various brands.

SUBSTITUTIONS. All the cobalt cerulean/turquoise paints are relatively dull, and therefore are fairly easy to approximate with a mixture of cobalt blue with cobalt teal blue (PG50), or ultramarine blue with phthalocyanine green BS (PG7). See also the section on cobalt pigments.

TOP 40 PIGMENT  Indanthrone blue PB60 is a lightfast to very lightfast, semiopaque, heavily staining, very dark valued, dull blue violet pigment, available from 13 pigment manufacturers worldwide. Discovered in 1901, it is the oldest vat dye. The correct name (for example, as used in the Handbook of Industrial Chemistry) is indanthrone; "indanthren" is an obsolete and generic term for a high quality vat dye of any color. Unrated by the ASTM, my own and manufacturer tests assign it an "excellent" (I) lightfastness. In watercolors, PB60 undergoes a very large drying shift, lightening by 50% (!) and losing saturation. As a lake pigment, it is used in paints, bank notes and automobile finishes. PB60 has a moderate to high tinting strength. The best mixing complements for indanthrone blue include most of the deep yellows, such as hansa yellow deep (PY65), benzimidazolone orange (PO62) and raw umber (PBr7). The average CIECAM J,a,b values for indanthrone blue (PB60) are: 18, 0, -32, with chroma of 32 (estimated hue purity of 35) and a hue angle of 271.

The pigment is fairly consistent across manufacturers. Even so, the Daniel Smith indanthrone blue is notably dark and lustrous, more intense and redder than other brands, transparent in tints with a very large hue shift toward blue. Holbein's paint is equally dark and the most intense of all. Both are redder than other brands. The Winsor & Newton and Rowney Artists paints are slightly less saturated with a greener hue; though the latter is darker and smoother. The Old Holland tends to bronze when applied full strength and is duller than the others. Schmincke misnames the pigment and offers a much darker, duller and impermanent color; I suspect some carbon black is mixed in, though this is not listed in the pigment ingredients.

Usually an inessential pigment, PB60 mixes muted violets or maroons with quinacridone carmine (PR N/A), and is an effective portrait or figure shadow color in tints, but its darks and shadows can appear grayish or obtrusive. Substitions. It is closely matched by many mixtures of dark blue and red, for example phthalo blue (PB15) with quinacridone violet (PV19) or quinacridone maroon (PR206). These mixtures are comparably as dark as PB60 and do not show as large a drying shift. PB60 is a useful alternative to dioxazine violet (PV23) for a dark blue violet color; by itself it is also an effective indigo or payne's gray hue in tints (see the recipe for synthetic black described under indigo paints). See also the section on anthraquinone pigments.

lightfastness test samples
unexposed (left); exposed 800+ hours (right)

Schmincke, Rowney

 The varieties of cobalt blue deep, indexed as PB72, PB73 or PB74, are all very lightfast, semiopaque, moderately staining, very dark valued, moderately intense to moderately dull violet blue pigments; offered by 4 pigment manufacturers worldwide (primarily for coloring ceramics and producing the deep "cobalt blue" in glassware). Unrated by the ASTM, manufacturer and my own tests assign it an "excellent" (I) lightfastness. In watercolors, PB72/74 undergoes a small drying shift, lightening by 10% and losing saturation. The tinting strength of cobalt blue deep is moderate. The best mixing complements are raw umber (PBr7), raw sienna (PBr7), quinacridone gold (PO48) and hansa yellow deep (PY65). The average CIECAM J,a,b values for cobalt blue deep (PB72) are: 29, -20, -62, with chroma of 65 (estimated hue purity of 67) and a hue angle of 252.

This group of pigments is a recently developed extension to the cobalt range, formulated with oxides of silicon or aluminum, that are warmer and darker valued than regular cobalt blue (PB28). These pigments are fairly similar across manufacturers, with some exceptions (Daler-Rowney). It is rapidly becoming more popular: now four watercolor brands offer it, most recently Daler-Rowney. (MaimeriBlu and some other brands offer a "cobalt blue deep," but these are within the range of cobalt blue PB28.) Winsor & Newton cobalt blue deep is the most saturated of the paints listed here; it keeps its deep warm hue even when applied full strength; it also has a lovely gentle flocculation that appears in all mixed greens, blues and violets made with it. Rowney Artists cobalt blue deep is unusual, close to the hue and value of a regular cobalt blue, but more saturated. The Old Holland paint is greener than the others and turns dull and blackish in masstone.

I sometimes prefer PB73/74 to ultramarine: it is just as lightfast but is less transparent, shows very little color shift as it dries, and creates a wonderful downy granulation in mixtures. It mixes perfectly with other cobalt pigments, providing a complete range of blue and green shades with the same textural and handling attributes. The main drawback: like ultramarine, cobalt blue deep will fade if exposed to mild acids (acidic atmosphere, lemon juice or vinegar may be strong enough). Worth investigating, if you want a consistent cobalt texture and lightfastness across all the violets, blues and greens in your palette. See also the section on cobalt pigments.

Although lapis lazuli can be acquired as a powdered pigment from some pigment retailers, Daniel Smith genuine lapis lazuli is the sole source of the pigment in watercolors. My sample of paint (and the lapis lazuli reflectance curve) looks exactly like a davy's gray — there is no discernable blue tone. This is apparently because Daniel Smith has simply pulverized and washed the raw lapis stone, rather than using the traditional pigment extraction method invented in and known since the 13th century; the grayish pigment instead resembles the extraction residue that in the 18th century was called "ultramarine ash.") The newer formulation, released in 2003, seems to have a coarser granulation in order to preserve the dark blue color. The tinting strength is very low. I am reluctant to buy it, at $16 a tube, because it does not resemble a good quality medieval ultramarine, and because the color compares poorly to both ultramarine blue (PB29) and cobalt blue deep (PB72), which provide much more reliable and cheaper modern substitutes with similar granulation effects. See also the section on natural inorganic pigments and the page on PrimaTek watercolors.

convenience mixtures made with blue pigments

Indigo was originally the anil dye that put the blue in blue jeans. As we know from the '60s, blue jeans fade because indigo pigment is fugitive, so substitutes have been found, mostly by mixing a dull middle or red blue (usually phthalo blue, prussian blue or ultramarine blue) with a black pigment (lamp or ivory black). The Daniel Smith indigo, made with indanthrone blue, is very evocative. Winsor & Newton gets the same blue violet indanthrone hue by mixing phthalocyanine blue with a violet quinacridone. Both the Rowney Artists and MaimeriBlu mixtures use a cooler dark blue. — It's particularly important with intense or very dark paints that you explore their handling and appearance in highly diluted mixtures. You may be surprised at what you discover. The indigos listed here shift toward a perfect metallic gray (DS) or pale green gray (MaimeriBlu) when applied as diluted washes. For the origin of natural indigo see the section on natural organic pigments.

Incidentally, a rich, transparent, extremely lightfast and flexible alternative to all carbon black and convenience dark neutral paints (indigo, sepia, neutral tint, payne's gray, etc.) is the generic mixture I call synthetic black. I originally developed this mixture using the additive (RGB) primaries indanthrone blue (PB60), benzimida brown (PBr25) and phthalocyanine green (PG7), roughly in the proportions 8:6:1, although any transparent, dull and/or dark red orange, green and blue or violet paint mixture will work fine. The reasons for using the additive primaries are that (1) they enhance the light canceling effects of subtractive mixture more than a mixture of the subtractive (CYM) primaries, and (2) the paint proportions can be varied slightly to shift the "black" mixture toward any hue of dark shade (as demonstrated in this painting).

However, if a potent, achromatic dark gray is the goal, then it is more efficient to use two mixing complements. The darkest and most efficient mixture along the red/green contrast consists of perylene maroon (PR179) and phthalocyanine green BS (PG7), roughly in the proportions 5:1; along the orange/blue contrast the darkest mixture is quinacridone orange (PO48) and iron blue (PB27) in roughly 4:1 proportions. (Exact recipes depend on paint brands; alternative mixtures are listed in the page on watercolor mixing complements.) Daniel Smith, M. Graham, and Da Vinci offer all four paints; Winsor & Newton, Rowney Artists and MaimeriBlu make a quinacridone maroon (PR206) that you can substitute for the perylene maroon and quinacridone orange.

In the correct proportions, either the three paint or two paint mixtures give an extremely dark, dead on black color; tweaking the proportions of the paints will shift the hue to mimic any commercial dark shade paint (sepia, perylene black, indigo, neutral tint, payne's gray), as well as dark shades that are magenta, turquoise or deep yellow. In masstone applications these mixtures are actually darker valued than most lamp or ivory blacks (PBk9). They create a velvety luster, rather than the usual carbon black dullness, that harmonizes well with other dark valued paints; they can be used to produce shades of any paint, and when applied wet in wet or used in diluted glazes, color separation among the pigments will produce subtle and shimmering color effects.

KEY TO THE PAINT RATINGS. Summarized as numbers: Tr = Transparency: 0 (very opaque) to 4 (transparent) - St = Staining: 0 (nonstaining) to 4 (heavily staining) - VR = Value Range: the value of the masstone color subtracted from the value of white paper, in steps of a 100 step value scale - Gr = Granulation: 0 (liquid texture) to 4 (granular) - Bl = Blossom: 0 (no blossom) to 4 (strong blossom) - Df = Diffusion: 0 (inert) to 4 (very active diffusion) - HA = Hue Angle in degrees of the CIELAB a*b* plane - HS = Hue Shift as the undertone hue angle minus the masstone hue angle, in degrees of the CIELAB a*b* plane - Lf = Lightfastness: 1 (very fugitive) to 8 (very lightfast) for paint in tint,full strength - Mentioned in pigment notes: Chroma: For the masstone paint on white watercolor paper. - Drying Shift: Change in masstone color appearance from a glistening wet to completely dry paint swatch, in units of lightness, chroma and hue angle in CIELAB. For more information see What the Ratings Mean.

Last revised 07.I.2015 • © 2015 Bruce MacEvoy