© Richard Perry/The New York Times
The element chromium gains its name from the rich colours seen in many of its salts and compounds. One of them, chromium oxide, was discovered in about 1798 by Louis-Nicolas Vauquelin, who immediately recognised its future use as a pigment, because of its “fine emerald colour”. But painters were still enamoured with more toxic greens, and straight chromium oxide doesn’t look particularly brilliant, being a rather dull yellow-green. Its introduction into paintings probably didn’t start until around 1840, when landscape painting outdoors was becoming all the rage.
Some of the earliest paintings known to use chromium oxide are those of Moritz von Schwind, of which the first example that I can show is his Mermaids Watering a Stag from about 1846. He seems to have used the pigment quite extensively here in foliage, although probably in combination with other pigments.
Von Schwind’s King Krokus and the Wood Nymph from about 1855 is a clearer image, where he probably used chromium oxide in combination for most of his greens.
As these works were being painted, an improved version of chromium oxide was being developed: hydrated chromium oxide, which became known as viridian during the 1860s. This first became available at a reasonable price after Guignet started to make it in quantity in 1859, so has also been known as Guignet’s green. It’s sometimes termed émeraude or emerald, which only serves to confuse viridian with copper acetoarsenate, more widely known as emerald green.
Viridian came into use during the 1860s, and has proved far more popular than chromium oxide. Both pigments are reliably lightfast, opaque, and have good covering power, but viridian is the more intense, and doesn’t appear dull like plain chromium oxide.
Anselm Feuerbach’s painting of Paolo and Francesca from 1864 is one of the earlier works found to contain viridian among its many rich greens.
The best example showing off the colour of viridian is perhaps Édouard Manet’s The Balcony (1868-69), where he appears to have used the pigment throughout the blinds and railings, most probably mixed with lead white, and unmixed for the woman’s parasol.
Arnold Böcklin’s Triton and Nereid from 1874 is unusual in several respects. It’s reported as being painted in tempera rather than oils, but its deep lustrous greens were developed using a base of predominantly viridian, over which Böcklin applied a copper resinate glaze.
Pierre-Auguste Renoir’s La Yole (The Skiff) of 1875 uses viridian as the main colour for the reeds in the left foreground.
Analysis of Claude Monet’s series of paintings of the Gare Saint-Lazare in 1877 has revealed extensive use of viridian in mixtures, including the green shadows in the roof. In Arrival of the Normandy Train, Gare Saint-Lazare (1877), the pigment is apparent (and confirmed) throughout the green foreground of the platform, an optical effect resulting from light passing through the glass roof of the station.
Renoir used viridian together with malachite green and other pigments for the greens in his Chrysanthemums (1881-82).
If you care to spend some time examining the myriads of tiny dots in Georges Seurat’s monumental Divisionist painting of A Sunday Afternoon on the Island of La Grande Jatte (1884-86), I’m assured that you’ll find many of those forming its vegetation contain viridian.
Viridian remained popular among the post-Impressionists, from whom I have two well-known paintings as examples.
Vincent van Gogh included viridian in the pigments used in the range of greens in his A Wheatfield, with Cypresses (1889), which is more unusual for his use of ultramarine blue mixed to form green.
Paul Cézanne is known to have had a strong preference for viridian as one of the key colours in his palette. However, in his Hillside in Provence (1890-92), it is emerald green that is the more prominent, and the major part of the painting’s more brilliant greens, even into its pale turquoise sky. Some green passages, such as the patch of yellow-green grass at the edge of the path in the foreground, at the right edge of the canvas, have been built with a base of lead white and viridian, over which he has applied a yellow lake glaze.
Chromium oxide and viridian remain widely available today; although the former is not popular or widely used, viridian remains a mainstay green widely recommended for its colour and other properties. Being virtually insoluble, chromium oxide and viridian pose minimal risks of toxicity to the artist. However, there is growing concern over their environmental effects, and great care is needed when handling waste paint containing either pigment.
Reference
Richard Newman (1997) Artists’ Pigments, vol 3, ed Elisabeth West FitzHugh, Archetype. ISBN 978 1 904982 76 0.
In addition to reading laid-out documents, the most popular purposes for PDFs are forms and annotation. As far as filling in PDF forms are concerned, I have just one word to say: Fillably, Joel Norvell’s outstanding app available from the App Store, which transforms Preview into the ideal platform for tax and other forms. Rather than struggling with the tangle of tools in a general PDF editor, Fillably provides the perfect suite for creating PDF forms.
Annotating PDFs is more complicated, though.
Annotations aren’t an afterthought, but a central part of PDF. All PDF documents consist of a list of hundreds or thousands of objects of different types, including annotations of the Annot type, and those are listed in one of the file’s standard dictionaries, its Annotations Dictionary, Annots.
There are at least 27 sub-types of Annot, including Caret, Highlight and Stamp, which are reflected in the annotation tools provided by apps from Acrobat to Preview. Seemingly complex annotations like popup notes are straightforward to code in PDF, requiring just two linked objects, one for the popup and its text, the other to specify its placement on the page. Others are more involved, as they can extend to include file attachments, sound, movie and other multimedia.
Despite their original simplicity, there are multiple problems that can arise with annotations.
With more recent versions of PDF, the ways in which they can be coded has increased. Mark up a PDF using the latest versions of Adobe Acrobat Reader or its ‘Pro’ CC colleague and they’ll cast it in PDF-1.6 and you’re unlikely to see a single Annot in their source. Most apps built on the Quartz PDF engine should write their files in PDF-1.3 so they can be accessed more widely, and should use regular Annot sub-types throughout. However, Preview likes to use opaque AAPL:AKAnnotationObjects that you won’t encounter anywhere else.
What Quartz does is to ‘flatten’ each PDF into a common 1.3 format for rendering, and that can be saved to disk. At present, that seems to work faithfully, but might give the impression that macOS can’t render more recent versions of PDF, which isn’t true. You can demonstrate that by opening an Acrobat PDF-1.6 document using an app that relies on the Quartz engine, such as PDF Expert, Preview or my Podofyllin, and comparing that with the original in Acrobat.
Podofyllin has a convenient feature for doing just that, in its source window. The uppermost of its three views displays Quartz ‘flattened’ code in PDF-1.3, the middle shows the original, here in PDF-1.6, and the lowermost is a summary of the latter.
The biggest dangers with annotations arise because of PDF’s ancient origins and a file format that doesn’t make sufficiently clear distinction between data and metadata. All annotations are metadata added to the underlying document, but in PDF, objects for each are mixed freely within the source. When they’re clearly distinguished with the Annot type, they should be easy to remove as a group, and PDF Expert offers that as a convenient command. That’s ideal when a document has been developed with the aid of reviewers’ annotations, to prepare the finished version for release.
Unfortunately this can cause its own problems, as PDF source is notorious for retaining old content that’s no longer visible in the rendered document, but can be read by anyone with a little knowledge about PDF. Like incomplete redactions, such hidden annotations have caused many embarrassments in the past, and will continue to catch folk out.
Finally, Preview has had more than its fair share of bugs in handling PDF annotations. During my research for this article, Preview 11.0 (1069.7.1) in macOS 15.6 was generally well behaved, but did mangle comments added to a test document by PDF Expert and Adobe Acrobat. Preview has two behaviours that can appear disconcerting: that of its Highlights and Notes tool, and its use of versioning.
All Preview’s tools are single-shot apart from Highlights and Notes, the drawing pencil icon to the left of its popup menu. Click this once to apply highlighting to selected blocks of text, and to remove existing highlighted sections. Unfortunately when this tool is turned on, its own highlighting is so weak that it’s hard to see.
Preview has a habit of saving PDF documents automatically when closing them, without any warning. If it has just mutilated an annotation, for example, you might assume the original file has just been overwritten and lost. However, Preview saves PDFs using the macOS document versioning system, so you can always recover the previous version.
This might at first seem an impossible task: use Preview to restore that old version and it will repeat its mutilation, defeating the purpose. Yet the original PDF editor won’t have access to previous versions, as it doesn’t use the versioning system. The solution is to use Revisionist, or Versatility, which can save the original as a separate document.
For all its toxicity, vermilion proved an enduring red, unlike less dangerous pigments such as crimson, with its natural origin.
People have dyed their clothes and other fabrics using vegetable colourants for as long as we have evidence. Dyes are quite unsuitable for use in durable paintings: instead of solutions of small molecules of colourant that work well applied to fabrics and paper, we much prefer to paint using pigments, in which the colourant is packaged and protected in much larger particles.
One of the early challenges in the history of art materials was the transformation of vegetable dyes into pigments, in a process generally known as laking. The need was simple: take a vegetable dye such as the crimson derived from Madder plants, and fix it into pigment particles that can be dispersed in gum solution for watercolour, or a drying oil medium.
Neither the Romans nor the Greeks appear to have solved this on any scale, but at some time between the Classical civilisations and the pre-Renaissance, someone discovered that aluminium salts will combine with the colourants in madder extract and make a pigment suitable for fine art painting, in madder lake.
Over time, many different recipes for the preparation of madder lakes were evolved. By using different species of Madder plant, adjusting the method of extracting the colourants from its root, and using different salts for the laking process, madder lakes covered a broad range of hues from pale purples through pinks to brilliant scarlet.
As a result, madder lakes were very widely used, and generally sought-after, except that they weren’t lightfast, even when protected in an oil paint film, and many faded rapidly, over months or just a few years.
Friedrich Herlin’s High Altar made for the church of St Jacob in Rothenburg in 1466 is one of the earliest paintings in which madder lake has been demonstrated. Its abundant reds seem to have stood the test of time, although because Herlin’s painting was normally stored with its wings closed, its madder lakes will have had limited exposure to bright daylight.
The two or three different shades of red used by Herlin in the panel of The Presentation of Christ in the Temple are still brilliant, although something odd appears to have happened in the blue robes of the Virgin Mary.
The Mass of Saint Hubert, the right hand shutter of the Werden Altarpiece from about 1485-90, has also retained its deep madder lake reds.
Madder red was mixed with a little lead-tin yellow for the sleeve (at least) in Altobello Melone’s Christ Carrying the Cross, dating back to about 1515.
Niklaus Manuel’s Demons Tormenting St. Anthony, on the left wing outside from the Antonius Altar of 1520, features several different reds, at least one of which contains madder lake as its main pigment. It also appears that some of those reds may have faded: Saint Anthony’s cloak looks pale and anaemic, for example.
Jan Vermeer’s Christ in the House of Martha and Mary from about 1654-56 is a good example of the use of madder lake by one of the Dutch Masters.
When industrial chemistry started to look for improved dyes and pigments in the nineteenth century, attention turned to the humble Madder, in an attempt to isolate the most lightfast components of its root extract, then to synthesise them on an industrial scale.
The main colourant, alizarin, was isolated in impure form in 1826, following which rose-red alizarin lakes became available. The other major colourant, purpurin, was more of a mystery, as little was found in fresh root extract, but it was generated during manufacture and storage; its purification took a few decades longer to achieve.
I suspect that the delicate reds in Henri Fantin-Latour’s Still Life with Chrysanthemums (1862) owe much of their colour to partially-purified alizarin crimson derived from Madder root.
Alizarin was first synthesised in about 1869, became available as a pigment in its own right from 1891, and was considered to be both more consistent in its colour and more lightfast. However, its lightfastness didn’t prove as good as had been hoped, and since the late twentieth century the fading of alizarin crimson has been used in lightfastness testing to demonstrate that sufficient light exposure has occurred. It has effectively become the benchmark for non-lightfastness.
Modern professional watercolour ranges, here those from QoR, often include a paint designated as Permanent Alizarin Crimson, which doesn’t contain alizarin or any other derivative of the Madder plant.
A few ranges, including Winsor & Newton Artists’ Watercolour Sticks, do still offer genuine alizarin crimson (PR83). Unless you are content for that colour to fade on exposure to light, you should avoid using it in any significant work.
This is true even in oil paints, where ranges such as Williamsburg’s offer a Permanent Crimson using a more lightfast pigment.
It’s a great pity that the crimson used by Vermeer and extensively by JMW Turner has such fugitive colour. At least we now have several excellent alternatives.
Reference
Helmut Schweppe and John Winter (1997) Artists’ Pigments, vol 3, ed Elisabeth West Fitzhugh, Archetype. ISBN 978 1 904982 76 0.
Many yellow pigments in use, even into the twentieth century, have shown a pronounced tendency to fade. So when someone comes along offering you a ball of compressed powder that is an intense yellow, and appears more lightfast than alternatives, you’ll believe anything they say. It comes from the urine of cows? No worries, just tell me how much, and when can you deliver?
This seems to have been the story behind the introduction of Indian Yellow into European painting. It had a long track-record of use in and around the Indian sub-continent, where it had featured in watercolours and gouache, and buyers in Europe were only too happy to pay high prices for it when it became available.
This exquisite watercolour miniature showing a Mongol Chieftain and Attendants from the Gulshan Album now in the Freer and Sackler Galleries is a good example, from around 1600. Its yellows and greens have lasted those four centuries very well, and careful testing by Elisabeth FitzHugh has shown the unmistakable presence of the chemicals known to be diagnostic of real Indian Yellow.
The snag with European paintings is that so few works have been tested, and records are so scant, that we don’t even know when Indian Yellow was first used as far west as Europe.
Ernst Willers’ Grove Near Ariccia in the Evening Light (1873) is one of the few European paintings known fairly unequivocally to contain Indian Yellow, probably used to form its rich greens.
We know with rather greater certainty when Indian Yellow came off the market, as by the end of the nineteenth century supplies had essentially dried up. The claim is that, between the late 1500s and then, some Indian herdsmen fed their cows with mango leaves, collected the cows’ urine, and dried it to generate the pigment in balls of compressed powder, some of which still exist. In the nineteenth century, this was increasingly viewed as being cruel to the cows, and the practice was progressively eliminated.
Whether this story is accurate, or indeed the pigment ever saw much use, remains open to doubt. Certain claims, for example of a ban on the production of the pigment from 1908, can’t be verified and appear legendary. But there is evidence that some artists in both India and Europe used the pigment in their paintings.
Its successor Chrome Yellow is part of a family of pigments ranging from pale lemon to deep orange-red, and based on lead chromate, which had been ‘discovered’ as a mineral in the middle of the eighteenth century. Its use as a pigment wasn’t recognised until the early nineteenth century, when it became increasingly popular and versatile.
Initially, supplies were limited and it was expensive. As general commercial demand for the mineral increased, new sources of supply were found, and its price fell accordingly. During the latter half of the nineteenth century it was probably the mainstay yellow and orange in the palette of most painters.
The first evidence of the use of chrome yellow as a pigment in painting dates from just before 1810. Johann Friedrich Overbeck’s painting of Italia and Germania (or possibly Sulamith and Maria) was made in 1828, and is thus from the early adoption phase, when the pigment was expensive and encountered infrequently. Although Overbeck was restrained in his use of colours from orange through to yellow and green, he has achieved a subtle chromatic effect in the green fabric.
Carl Blechen seems to have used Chrome Yellow more extensively in his imposing View of Assisi, painted a few years later in 1832-35. By this time the mixture of Chrome Yellow with Prussian Blue had become known as Green Cinnabar or Chrome Green, although the chromium salt used was not itself green, of course.
By the time that Arnold Böcklin painted this, his first version of Villa by the Sea in 1864, Chrome Yellow had established itself as the standard. However, this is one of a relatively small number of works using the pigment in an almost encaustic mixture of resin and wax.
Chrome Yellow was widely used by the Impressionists and shown at the Salon, and is demonstrated well in Paul Cézanne’s famous painting of The Railway Cutting (c 1870). I believe that most if not all of the greens seen here rely on Chrome Yellow mixed with blue.
As some of the Impressionists, like Claude Monet, generated more income, they could afford to start using the newer and far more expensive cadmium-based pigments that were coming onto the market. Cadmium Yellow is also considerably more lightfast and durable than Chrome Yellow, so during the late nineteenth and early twentieth centuries, many painters switched away from Chrome Yellow.
Walter Crane’s Neptune’s Horses (1892) is one of the later works that apparently still relied on Chrome Yellow.
During the twentieth century, Cadmium continued to displace Chrome in pigments for paints ranging from lemon to orange-red. However, both are potentially environmentally damaging, and in this century more modern, less toxic synthetic organic pigments have been introduced as substitutes. Thankfully, as both Cadmium and Chrome pigments trap their toxic salts in insoluble particles, neither presents any danger to the careful painter when used in paint. For the pastellist, though, inhalation of pigment in dust is a more significant risk.
Chrome Yellow was one of the key colours of Impressionism, and features in many nineteenth century landscapes. No cows ever suffered in its manufacture.
References
NS Baer, A Joel, RL Feller & N Indictor (1986) Artists’ Pigments, vol 1, ed Robert L Feller, Archetype. ISBN 978 1 904982 74 6. (Indian Yellow)
Hermann Kühn, Mary Curran (1986) Artists’ Pigments, vol 1, ed Robert L Feller, Archetype. ISBN 978 1 904982 74 6. (Chrome Yellow)
A quick check of just one of my working volumes revealed that it contains over 20,000 PDFs, the earliest dating from 1994, just a year after its introduction. Six years ago, I had become fed up with trying to use other PDF readers and set out to write my own, that soon became Podofyllin. It has some unique features, of which the most important to me is that it can’t and won’t change a PDF. Podofyllin is the latest app I have rebuilt, tweaked and given a new icon to, primarily for compatibility with macOS 26 Tahoe.
What I hadn’t realised was that, at some time during Sequoia, one of Podofyllin’s key features had quietly stopped working, apparently as a result of a silent change in macOS. This update fixes that, and restores (almost) full functionality, with just one feature still absent.
Perhaps its most important feature after preserving original PDFs unchanged, is its support for opening multiple views of the same document. Shown above are three different windows, each showing the same document, and at the lower left Writing Tools is just about to produce a summary from one of them.
The main window has thumbnails on the left, a conventional rendered page view in the middle, and the whole text content to the right. You can also open an unlimited number of accessory windows, each displaying different pages from the same document.
Another unique feature (the recently troublesome one) is a window to display the contents of the PDF file in raw format, so you can inspect its structure, metadata, and more.
This source code window shows two versions of the code, one as written in the file, the other ‘flattened’ as used in Quartz 2D to render it, together with a summary. Quite a few PDFs contain hidden content, usually left over from an earlier edit. Some save contents in versions, and for those Podofyllin can recreate and save those as separate PDF documents.
The one feature that used to work in the past that I still can’t revive is exporting page contents in Rich Text format, something I suspect isn’t working in macOS.
I have also taken the opportunity to overhaul the Help file thoroughly, to make it more accessible and navigable.
Podofyllin 1.4 is now available from here: podofyllin14
from its Product Page, and via its auto-update mechanism.
Like other recent updates, this new version requires Big Sur or later. If you’re still running Catalina or earlier, please check Podofyllin’s Help document, as that explains how you can disable its auto-update mechanism.
I’m delighted to welcome the prodigal Podofyllin back at last.
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