Phthalocyanine blue (PB15) is an incredibly intense, staining, transparent, non-granulating, lightfast pigment that comes in two versions:
- Phthalo Blue Green Shade (PB15:3)
- Phthalo Blue Red Shade (PB15:6 or PB15:1)
(I’ll call them GS and RS in this post.)
What’s the difference, and which should you choose?
The main difference is the hue. Both colors have the same properties (intense, staining, etc.)
GS is, as you might expect, greener-toned. It’s as close as you’ll get in watercolor paint to a true primary cyan. It makes lovely clean greens and other bright mixes.
RS is similar to what you’d get if you added a bit of red to GS. It’s by no means purple, just a sort of middle blue. In terms of hue it is similar to Cobalt Blue.
One of the struggles with posting about this is that my camera steadfastly refuses to demonstrate the differences in hue. These look more different to me in person, but on camera they look more similar. (So, if you plan to mostly photograph your work, the difference is effectively negligible.) Observe the middle tone in the above photos, though – the bright cyan in the left is characteristic of GS.
Getting from One to the Other
I got a decent RS hue by taking GS and adding a bit of magenta (in this case Purple Magenta PR122). It looks to me like a nice clean middle blue.
I wasn’t as big of a fan of the GS hue I got by taking RS and adding a bit of Phthalo Green (PG7). This is predictable from color theory since cyan is a primary.
Intensely bright, near-neon spring greens, teals, mints, and aquas with RS; much more muted greens from RS. GS + LY is what you want to paint a Lisa Frank neon dreamscape, and RS is probably more what you want to paint a realistic landscape that’s still bold and bright.
Rich Green Gold
Wow, this one shows a huge difference, from bold bright greens and teals in the GS mixes and muted Sap Green/Prussian Green hues with RS. (Granted, switching brands on the Green Gold might have had an effect too. It seems that the DV PY129 may be more muted than the DS.)
Cleaner, brighter purples from RS.
Similar teals with wide range of values, though the GS ones are brighter and more vivid.
Both shades of Phthalo Blue tend to be in same price series, which means there should generally be no price difference between them within the same brand (though prices between brands can vary depending on your locality.)
- Daniel Smith lists both Phthalo Blue Green Shade (PB15:3) and Phthalo Blue Red Shade (PB15:6) as series 1.
- Winsor & Newton lists both Winsor Blue Green Shade and Winsor Blue Red Shade as series 1.
- Da Vinci lists both Phthalo Blue (PB15:3) and Phthalo Blue Red Shade (PB15:1) as series 3 (they have a different series scheme than DS/WN, so this does not necessarily mean they’re more expensive than DS – in my locality they’re cheaper. YMMV.)
- Holbein lists both Phthalo Blue Yellow Shade and Phthalo Blue Red Shade as series A. (See, they all have different series numbering.)
- Schmincke Horadam lists its primary PB15:3 (Helio Cerulean) and a PB15:1 (Phthalo Blue) both as series 1, however it also has a Phthalo Sapphire Blue (PB15:6) which is series 2.
When I asked What’s the best blue watercolor for the sky?, I came to the conclusion that the overall winner was Phthalo Blue Red Shade. Indeed, in my recent sky practice, I found RS a very useful convenience color – especially for, say, a sunset sky where a blue fades into a yellow-orange. Starting with GS can lead to unwelcome bright greens, where a delicate touch with RS turns into a more sky-appropriate muted blue.
GS, by contrast, is far to green for this use case and needs to be muted before using. But it is easily done: adding nearly any red to GS quickly mutes it to a nice blue-purple tone.
GS can also be used for wonderfully bright sky horizons, where RS is not inspiring.
In general mixing, GS is better: as a primary, it is simply a more versatile mixer.
Before I did this post, I was leaning toward RS as a more useful convenience color for me, with GS as a better mixer to recommend for general use; but after playing around and seeing how ridiculously easy it is to get to an RS hue from GS and not vice versa, I’m actually planning to stick with GS on my palette.
Parka Blogs: Phthalo Blue (Green vs Red Shade)
Scratchmade Journal: Comparing Blue Watercolors – Phthalo Blue