The family of pthalocyanine pigments, commonly called pthalos or thalos, come in a number of blue and green shades. They are beautiful, lightfast, transparent, and high in chroma. But I don’t use them.
The reason is that they are too bloody strong. Pthalo blue is something like 40 times as strong a tinter as ultramarine blue. That means, for example, that in order to change the color of titanium white by 10%, you would add 40 times as much ultramarine blue as pthalo blue. That sounds like a good thing (efficient!), but in fact it’s infuriating. In mixing, it is extraordinarily difficult to add a small enough amount of a pthalo color to get the effect you’re looking for. Paint manufacturers reduce this problem somewhat by adding colorless extenders to some pthalo paints, but that only goes so far. Some artists learn to manage with pthalos (they are, in fact, quite popular artist’s colors), but I hate trying to work with infinitesimal amounts of paint when trying to make subtle changes to mixtures, so they drive me nuts.
Fortunately, there are good substitutes. Prussian blue is almost exactly the same hue and transparency as a neutral (not green or violet) shade of pthalo blue, but a lot less strong. And viridian is very similar to a neutral pthalo green. So if you have trouble mixing with pthalo colors, try those instead.
Tags: art materials, color, egg tempera painting, oil painting, painting
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But isn’t real Prussian blue a fugitive pigment? I prefer it too, but I’ve been led to believe that pthalo is its replacement.
I don’t care to use the pthalos, either. I don’t even own pthalo green.
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Dorothy,
Great to hear from you. I’ve enjoyed your blog (it would be great if you’d post more often—hint, hint).
Your point regarding Prussian blue is a good one. The ASTM rates Prussian blue as having the highest lightfastness rating (excellent or I). They are usually very reliable for tests of this sort. There is a good discussion of Prussian blue as a watercolor pigment at the excellent Handprint website:
(http://www.handprint.com/HP/WCL/waterfs.html
In summary, the author’s lightfastness tests indicated that some brands show a slight discoloration within two weeks, but no fading after that. Other brands demonstrate no fading at all.
Generally (but not always) pigments display their worst lightfastness in watercolor and show much better results in heavier media such as oil and acrylic. Overall, I am very comfortable using Prussian blue from good manufacturers in those media. I’d be more careful with watercolor, but it seems that the better brands produce good results in that medium as well. I don’t have any in raw pigment form and would be very careful about selecting the company I purchased it from if I did.
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You are so mean to pthalo blues. I love, love, love it for its intensity.
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Sue,
If it works for you, then great. I find pthalos much too strong.
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Nice article on chroma, etc. I agree with you about the books on color with lots of verbage and nothing really usable to be extracted. Oy is right. I like your knowledgeable straight forward tell it like it is style. Thank you.
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One thing to consider when mixing these blues is rather your desired end result is a transparent or opaque color….
Ultramarine and thalo blue are both transparent to varying degrees and you must consider that if you are going to mix more ultramarine blue with white then the resulting mix is going to be that much more transparent than it would have been with thalo blue.
Also I was under the impression that prussian blue was extremely lightfast. -
Andy,
If pthalos work for you, then you should certainly use them. I would not substitute ultramarine for most varieties of pthalo blue, as they are distinctly different in hue. Prussian blue works very well for that purpose, however.
Did you mean fugitive? Historically, there have been a number of slightly different ways to manufacture Prussian/Milori blue. Some variants have tended to fade. It’s my understanding, however, that modern versions of the pigment are acceptably lightfast. See my response to Dorothy, above.
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No I did not mean fugitive…I was referring to your comment to Dorothy above where you stated that the ASTM regarded it as lightfast!
I remember reading somewhere that some pigments are more stable in oils and acrylics because these binders help to shield the pigment from reacting with atmospheric conditions.In regards to my statement concerning pthalos vs. ultramarine, I didn’t mean to show favor over one or another pigment but I instead was trying to point out that there are other reasons for choosing a pigment besides the hue and that as artists that gives us more ways to create artwork! I love all the blue pigments….I love blue! I dont think I could consider deleting any of them from my pallete.
Also the colorless extenders you mention in the article above are commonly added to paints to displace the amount of pigment and thereby reduce the cost of manufacturing.
Some of you that find a paticular pigment too powerful might consider first mixing it with some sort of colorless medium to reduce it’s potency then using this resulting mixture to add to the main color your wanting to modify!P.S. I love your website! I like the practical approach that is rare to find in most art related forums!
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Andy,
I’m sorry that I parsed your comment incorrectly.
I, too, am a big fan of blues. That’s one reason why I buy paint from Robert Doak, whose blues are unique and wonderful. I would hate to do without them.
In most cases, extenders are added to paints for exactly the reasons you specify. With very strongly-tinting pigments, however, another reason may be to make them easier to mix with. The idea of adding your own extender in this case is a good one.
And thanks for the kind words. I appreciate your participation here. Please keep doing so.
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