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LuxeSci Show Notes: S2E5 - Yellow and Orange

Hello again.  Welcome back to LuxeSci, a podcast to re-ignite your wonder by exploring the science of luxury.  


Before we start today, just a reminder to check out our new website, www.erevnamedia.com 



We’re still in the bright and sunny, if not ridiculously hot season here in Greece so today we’re going to talk about the bright and sunny colors of yellow and orange.  I will add a note that we both found the website ColourLex extremely helpful (link in show notes).  Not only does it catalogue a wide range of pigments, it also features artwork using that pigment.  We’ll post some of those on our Instagram and Twitter.


Yellow

Yellow is one of those colors that has found an extreme following among painters who wanted to capture the light of the sun, moon, and stars. Van Gogh's Starry night is one example of the most well known uses of yellow in art.


Early Yellow

Based on yellow ochre. The main color giving component of natural yellow ochre (ocher, yellow earth) is limonite which is not a single mineral but a mixture of several iron-containing minerals among them goethite, akageneite, lepidocrocite, and jarosite, goethite (iron oxide hydroxide α-FeOOH) being the main component.

Iron oxides are stable at high temperatures but not resistant against acids. The pigment is absolutely stable as is documented by the cave paintings still in excellent condition after many thousands of years. It is compatible with all other pigments and is often used in mixture with other paints.

Example of use: Rafael Sistene Madonna



Gamboge:

Gamboge is a natural resin produced by trees in southeast Asia. Its main coloring components are the two substances shown below:


β-Guttilacton


Gambogic acid

The pigment is transparent and can be used in oil painting as a glaze. It changes its color to orange in contact with alkalis and is not very lightfast. It is not compatible with alkaline pigments and possibly with lead white.


.in use since around the 8th century in Japan and China. Its use in European oil painting is not very well documented but an example is: Rembrandt van Rijn, Saskia van Uylenburgh as Flora, 1641


Orpiment:

Orpiment is yellow arsenic sulfide with the formula As2S3. It occurs naturally as a mineral and can also be prepared artificially. The pigment is not very stable and decomposes slowly in contact with water, it is, however, more stable when dry. It is considered fairly lightfast but it can in some cases darken considerably and it is not compatible with lead and copper pigments.

Paolo Veronese, Allegory of Love – Happy Union,

Modern Yellows

As yellow pigments developed throughout history in a desperate effort to find a true, bright and lightfast one, new lead-based versions including Lead Tin Yellow  (a lead-tin based yellow Pb2SnO4), Naples yellow antimony- added (Pb2Sb2O7), TurnersYellow (Lead Chloride Oxide in 1781) and chromium yellow (PbCrO4 · PbSO4) Became popular.

Naples Yellow ended up being one of the most popular as seen in the coloring of the golden chairs in the work by Édouard Manet, Music in the Tuileries Gardens 1862





Indian Yellow Pigment

One yellow that was used throughout Europe from the 17th century was Indian Yellow. Thought to be made from the urine of cows, which were fed exclusively on mango leaves, it was considered cruel to feed cows mango leaves and eventually banned in England in the early 19th because of the detrimental effect of this diet. Indian Yellow today is a synthetic mixture of Nickel Azo, Hansa Yellow and Quinacridone Burnt Orange and is far more lightfast than the original. It is also known as Azo Yellow Light and Azo Yellow Deep.


Detail from ‘The Jewish Bride’ by Rembrandt

Lead Tin Yellow was the yellow of the day for Artists such as Rembrandt and Vermeer. Although known to have been used by Venetian Artists such as Giotto, Veronese and Tintoretto, the Dutch really popularized this yellow in the 17th Century. It is a bright yellow with good covering power and lightfastness but, as the name suggests, is very toxic due to its lead component and Naples Yellow became the more commonly used yellow.


Turner’s Yellow Watercolour

Turner’s Yellow is a pigment that is produced in a variety of shades from bright yellow to orange. Contrary to the popular belief that the pigment was named after artist, James M W Turner, it was actually named after James Turner- who patented the name in England in February 1781. Although the colour was first discovered in 1770 by Swedish chemist, Carl Wilhelm Scheele. The yellow pigment was made by grinding together two parts of lead and one part of sea salt into water. The mixture was allowed to stand for twenty-four hours before a caustic soda solution was poured off and the remaining white substance was heated (and dried) until it reached the desired shade of yellow. This Yellow pigment was widely used in England during the 19th Century and was regarded as durable and bright, in spite of a known tendency to blacken. It was claimed that it worked well in both oil and watercolor but noted its impermanence in sunlight.


Modern Yellows

Zinc Yellow: Also known as Ultramarine Yellow

inc yellow is a complex zinc potassium chromate with a formula of K2O · 4 ZnCrO4 · 3 H2O.

The pigment is soluble in acids and in alkalis (1), but it is not very lightfast and can change its colour to gray-green due to the reduction of the chromate ion to chromium 3+ ion (1). Newer research shows that it can also change its colour to dirty brown due to the reaction of the chromate ion to dichromate ion. 

Reminder: chromates and dichromates are highly toxic chemicals


Ochre brown dots in the grass are due to the decomposition of zinc yellow


Lemon Yellow

Lemon yellow is a barium chromate with a formula of BaCrO4 /The pigment is rather lightfast but can change its colour to gray-green with time due to the reduction of the chromate ion to chromium 3+ ion. All chromates and dichromates are highly toxic chemicals.

Boating on the Seine, Pierre-August Renoir, 1879



Arylide Pigment 

Also known as Hansa Lemon Yellow, discovered in 1909 by Hermann Wagner in Germany. It started to be commercially available around 1925 and more widely used predominantly as a replacement for the toxic cadmium yellow after 1950.



\\


SO much yellow info




Orange

  • Last year around this time we did a whole episode on oranges as part of our holiday series.  If you’re curious why we choose oranges, go listen to the episode. There’s a very personal reason why I associate oranges with the Christmas season

  • We see orange color with light in the 585 to 620 nanometer spectrum

  • Quick aside = back when I was in the lab, we used a instrument called a flow cytometer which measured fluorescence on the single cell level.  We used antibodies stained with flourescing dyes to look at various markers on the cell surface or inside the cell.  When  designing an experiment, I would have to look at the emission spectra of each dye to make sure they didn’t overlap too much and cause confusion between the markers and seeing these numbers always reminds me of that so shout=out to all my fellow immunologists.

  • In Europe and the US - orange is most commonly associated with amusement, warmth, energy, danger, taste, aroma, extroversion, the unconventional and anything Fall related

  • Interestingly, the true complementary color for orange is azure (between blue and green on a color spectrum).  Yellow is the complementary color for tru blue.

  • In painting though - blue is the complementary color to orange

  • Vincent van Gogh wrote “the oppositions of blue with orange, of red with green, of yellow with violet…trying to make the colors intense and not a harmony of grey”.

  • Makes each color appear brighter

  • The earliest orange pigment is likely orange ochre, found in paintings as early as 20,000 BCE.  We’ve mentioned ochre on previous podcasts.  As a reminder ochre is natural clay pigment.  Orange ochre occurs when limonite is present in the clay.  

  • Limonite - mixture of several iron-containing minerals including, goethite, akaganite, lepidocrocite and jarosite.


Realgar

  • One of the first non-ochre orange pigments is realgar, used around 1350 BCE, and popular in the Byzantine Empire

  • Monoclinic arsenic sulfide mineral

  • Brilliant red

  • As4Sf

  • Well-formed regular crystals that look like red gemstones

  • Also called “ruby arsenic”

  • Very soft - so it can be ground into powder

  • The pigment is not very light-fast and can be turned into orpiment when exposed to light

  • The only pure orange pigment until the invention of modern dyes

  • Fun fact - was used by firework manufacturers to create white in fireworks before powdered metals were available

  • The ancient Greeks knew it was poisonous but apparently that knowledge was lost for a little while.  When it was rediscovered, realgar was used as rodent poison, insecticides and weed killers


Orpiment

  • I’m bridging the color gap here to talk about orpiment, which is a yellow-orange pigment 

  • Orpiment is another monoclinic arsenic sulfide with the chemical formula of As2S3

  • Like realgar - it is soft and easy to grind into a powder and it was also used as a insecticide and rat poision


Chrome Orange

  • Chemically, Chrome orange has the chemical formula Pb2CrO5 

  • Very light fast and darkens with age

  • Sensitive to acids but more resistant to alkalis

  • Treat a lead salt with an alkaline solution of a chromate 

  • Control the shade of the orange by controlling the pH of the pigment


  • Discovery

  • Discovered in 1765 in the Ural Mountains, the mineral crocoite (lead chromate). 

  • The pigment was introduced around 1809

  • Brilliant reddish-orange four-sided crystal

  • Too rare to be used commercially

  • 1797 - Louis Vauquelin produced chromium oxide by mixing crocoite with hydrochloric acid and previously he isolated elemental chromium

  • He was the scientists that discovered that chromium compounds can form reds, yellows, oranges and even greens

  • Remember from our gemstone episodes that traces of chromium produce the deep green of emeralds and the deep red of rubies

  • Chromite ore deposits in the Ural Mountains led to a spread of chromium chemical factories to supply the paint industry

  • Today though - ⅓ - ½ of the chromite ore produced is from South Africa, wich Kazakhstan, India and Turkey also being top producers. 

  • Example

  • A great example of chrome orange can be found in Frederic Leighton’s “Flaming June” where a women’s is napping on a sofa and her dress is all Chrome Orange from 1895

  • Renoir’s The Skiff - where the boat features chrome orange. From 1875


Later pigments

  • Cadmium and antimony call also be used to produce orange pigments.

  • Cadmium is interesting since it can come from a mineral known as greenockite, which forms hexagonal crystals that grow straight up

  • The pigment is made industrially by reacting cadmium salt with sodium sulfide and sodium selenide

  • More selenium equals a darker orange


Glossary


Fun facts:

  • What is another use for the pigment realgar?

  • What element is responsible for the colors of both rubies and emeralds, in addition to being an orange pigment



Thank you again for listening to this episode of LuxeSci.  As always, many thanks to my cohost and audio engineer, Dimos.  OUr theme music is Harlequin Mood by Birdie.


You can follow all over social media at LuxeScipod.  Definitely give us a follow as we’ll be posting pictures of the crystals that form some of these pigments as well as paintings that feature the pigment.


Your assignment for the next two weeks: leave us a review on Spotify, Apple Podcast, Youtube or wherever you listen to your podcasts.


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