Prussian (Paris) blue

There is controversy among artists about the lightfastness of Prussian blue (ferric ferrocyanide), the colour used during Picasso's blue period. It was on van Gogh's palette, too. Recent research shows that, when subjected to accelerated ageing, Prussian blue is extremely lightfast, as such. However, it strongly fades when mixed with a white pigment, especially with lead white or zinc oxide (cf. Samain et al. 2011, here). So, it is a problematic pigment, after all. Manufacturers say that it has highest permanence, but this is true only as long as it isn't mixed with white. So I suppose Picasso's blue masterpieces are losing their brilliancy today. Some of Matisse's paintings are deteriorating, too: "Jennifer Mass, head of the Scientific Research and Analysis Laboratory at Winterthur museum in Delaware, said that Le Bonheur de vivre, a famous series of paintings by Henri Matisse, are deteriorating rapidly. One version, at the Museum of Modern Art in San Francisco, is almost unrecognizable, while another version at the Barnes Collection in Philadelphia is closer to what Matisse painted. Again, the culprit was cadmium sulfide. Cadmium sulfide is not a long-lasting pigment. It starts on the artists' palette as yellow and, over years, fades to white." (Shurkin, 2014, here) So bad pigments are causing a cultural tragedy. Le Bonheur de vivre is a defining artwork. Matisse said that he, from then on, always painted the same picture. Later paintings were really only different versions of Le Bonheur de vivre. I have two large unopened tubes of Prussian blue, which is a beautiful transparent colour. Some artists love Prussian blue over all others. Now I'm conflicted about what to do. After all, it's easier to find motivation if one knows that the piece is going to last. A discussant says: "I have tested many brands of Prussian Blue (PB27) in oils and some faded dramatically in less than 3 months, while others, particularly Grumbacher's Pre-Tested Prussian Blue, showed no changes after a year of sunlight exposure." (here) Mats Winther References Samain, L. et al. (2011). 'Fading of modern Prussian blue pigments in linseed oil medium'. J. Anal. At. Spectrom., 2011, issue 5, 26, 930-941. http://pubs.rsc.org/en/Content/ArticleLanding/2011/JA/C0JA00234H#!divAbstract Shurkin, J.N. (2014). 'Science And Art Meet, Unveiling Mystery And Cultural Tragedy'. Inside Science (Nov 18 2014). https://www.insidescience.org/content/science-and-art-meet-unveiling-mystery-and-cultural-tragedy/2316

Cadmium sulfide pigments were commercialized after 1840 and were in the yellow to red range. Especially paler yellows were of poor stability on account of the manufacturing process. They could have up to 20% free sulfur content and they were rarely stable. Other processes could lead to darkening or chalking of the pigment: "Early forms were often unstable, darkening on exposure to air and light, or bleaching in the presence of moisture (Fiedler and Bayard, citing Friend). Cadmium sulfide pigments are also reported to discolour when used with certain copper- and lead-based pigments (particularly emerald Cadmium carbonate green, q.v.)..." (Eastaugh et al., "The Pigment Compendium - A dictionary of historical pigments", p.72) Modern processes make use of diverse precipitation modifiers, such as cobalt, nickel, etc. The principal approach is to form cadmium zinc sulfide. Luckily, modern cadmium pigments aren't very toxic. According to Wikipedia, a 1997 U.S. government study stated, in part, "After an exhaustive, independent review requested by Congress, we have found no evidence that exposure to zinc cadmium sulfide at these levels could cause people to become sick." Despite the fact that pthalo green is hurtful to the eyes, it is the most popular green among artists. Helen van Wyk ("Color Mixing") includes both phtalo green and phtalo yellow green in her standard palette. Green is difficult for some reason. Picasso said that he was never satisfied with the greens directly out of the paint tubes. Personally, there is one green pigment which I find satisfying as it is, although it is not very useful. This is chromium oxide. It belongs to the most permanent colours, wholly comparable to the earth pigments. Certainly, I can do without Prussian blue. Phtalo blue is lovely. I like to blend it with cobalt blue and mixed white. I like this blend so much so I have propped it into small glass jars that I bought on eBay. I wonder how much time oil painters spend blending colours? Perhaps it is a year or so of their life that is spent working colour with a palette knife. Since they are never happy with the colour that comes out of the tube, they should think of premixing the colours. Mats

Daler Rowney's "System 3" acrylic colour has Prussian Blue, but it is a mixture of Ultramarine Blue, Phtalocyanine Blue, and Carbon Black. They shouldn't use a traditional pigment name for a mixture of other pigments, because it is fakery. Talens's azo yellow is named "Cadmium Lemon (azo)", although there is no cadmium in it at all. All of Daler Rowney's colours that are named "Cadmium ..." have no cadmium in them. For instance, Cadmium Red is really Napthol Red. I found that Beckers phtalo green is actually a mixture of phtalo green and azo yellow (Benzimidazolone), which makes a more natural and neutral green. Pure phtalo green corresponds to nothing in nature, although natural greens emerge if mixed with cadmium orange. /Mats

The manufacturers will only fool the apprentice once. In every painting book we read that e.g. cadmium yellow is obligatory. So the beginner goes out and buys a tube. But soon he will learn to take account of the little code words, like "hue", "azo", or "imit." If these are not present, then the pigment name is printed on the tube, instead. I found out that Prussian pigment is "alkali sensitive" and that's why there is no genuine Prussian acrylic colour available today. Liquitex Prussian blue has been discontinued. It's the same thing with alizarin crimson and viridian. I suppose, alkyd oil colours is an alternative to acrylics, because alkyd dries much faster and is more transparent. Mats