Phthalo blue: cyan skies, blue lagoons, and teals galore. This transparent paint comes out of the tube almost black in some cases, but just a drop of oil or a touch of white will electrify its chroma. Powerful in both glazes and mixes, this is one of the most intense colors on the painter's palette, and some thought must be given to its use. However, it is hard to imagine what painters of the past would have given for such a clear cyan. Phthalo blue has a bit of complexity to it, but we are fortunate that there is a way to decode the differences between the varieties.

More chromatic than Prussian blue, generally more green-leaning than Ultramarine, and overall more powerful than the gentler genuine Cerulean, we'd consider this an essential color to the palette.

There are two main forms of Phthalo Blue, which are sometimes labeled Phthalo Green Red Shade or Green Shade, though both are solidly blue. This refers to the way the colors mix as the slight leaning to each color will make one or the other more suitable in different color-mixing applications. Phthalo Blue has a handful of variations which can thankfully be disentangled by an additional number that may follow the pigment code, such as PB15:1. The most common varieties are PB15:1 (red shade) and PB15:3 (green shade), however we'll talk about the others, too.

Ok, so normally we like mystery. But not when it comes to our Phthalo Blues, which can often be sorted out by adding a number to the pigment code. PB15 without an additional number means we are dealing with a mystery phthalo. Phthalo Blue comes in a handful of varieties which have different properties, and sometimes paintmakers don't specify them. The general pigment code for Phthalo Blue (this is the little letter-number combo printed on the back of the tube) is PB15. With phthalos there is sometimes an additional level of information-a colon with a number added to the code- which can tell a person more about its specific properties.

This additional colon is helpful for painters. While the two main varieties of phthalo are similar, they behave differently in mixes.

Here's a short run-down of the phthalos:

Phthalo Blue Red Shade - Most commonly PB15:0 or PB15:1. However we've seen any variety of Phthalo sometimes labeled Red Shade.

Phthalo Blue Green Shade - Almost always PB15:3

Here is a brief synopsis of the various Phthalo Blue pigment codes:

PB15:0 - A rare version of Phthalo Blue that is redder (in the one instance we know of it's labeled as Red Shade).

PB15:1 - A common version of Phthalo Blue (Red Shade)

PB15:2 - A rare version of Phthalo Blue that seems warmer, more like Red Shade. In the past, this type was used by Gamblin, and is currently used in Old Holland's Scheveningen Blue Deep.

PB15:3 - A common version of Phthalo Blue (Green Shade). Excellent for making teal mixes.

PB15:4 - We associate this with a more delicate cyan. It's commonly used in Manganese Blue Imitations. In one case it's labeled Red Shade, however in other cases it's labeled Turquoise. We've almost always seen it as a green-leaning clear cyan.

PB15:6 - In one case labeled Red Shade. May have slightly less reliable lightfastness, but we have not tested it specifically. It's a slightly different form of Phthalo than the others listed above.

The convention of Green Shade and Red Shade is a bit of a wild one, but we see similar patterns in the way other pigments are named. In general the Green Shade makes the best teals. The Red Shade is a bit more of a middle blue. Here the Gamblin, RGH, and Old Holland Blue Lake are listed as PB15:1 or Red Shade. It's interesting to note the difference with the lighter tinting Vasari Green Shade and Old Holland Scheveningen Blue, both PB15:3.

Will the paint be used in the lower layers of the painting? If so, consider a phthalo blue bound only in linseed oil.

Are you looking for the brightest cyans or teals? We recommend Phthalo Blue Green Shade (PB15:3) for mixing the brightest blue-greens.

And if the phthalo is too intense, consider cutting the mix with another color. Complements to phthalo which can also tone it back are oranger versions of PR101 and Cadmium Orange PO20.