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LuxeSci Show Notes: S2E4 - White and Purple

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 There are new blog posts on there!


So last time we discussed black and blue pigments.  Dimos - which ones are we covering today?  That’s right, white and purple.  One that’s relatively easy, if toxic, to make and one that’s a little more challenging.


Where do we first see the color white in painting?


White was one of the first colors used in art, with prehistoric cave drawings, such as those at Lascaux in France, featuring marks and images made using calcite and chalk.

And this cave also provides us with the earliest example of humans using white pigments. It’s thought that the cave paintings were created around 17,000 years ago.

Ancient Mesopotamians held the color white in high regard. Remaining records from this period even describe how the walls of the great priest-king’s homes were painted white with gypsum. 


Most people have heard about the Great Pyramid. But what’s less well known is that it was originally covered in about 5.5 million tons of white limestone. 


In Ancient Greece white was a sacred color, representative of light and the milk of mothers. In Rome, a plain white toga, toga virilis, was worn by all Roman citizens at ceremonial occasions, and togas brightened with white chalk, toga candida (the origin of the word “candidate” and the original meaning being “bright white”), were donned by those seeking public office.


A not so white paint that has its root in ancient origins is Gesso.


An aside---”Gesso is an important art supply to get your canvas ready for painting. You can buy gesso readymade from any art supply shop. Gesso is very similar to white acrylic paint, only thinner as it is made of gypsum, chalk, and a binder. It dries hard, making the surface more stiff. Gesso prepares (or "primes") the surface for painting, making the surface slightly textured and ready to accept acrylic paint. Without gesso, the paint would soak into the weave of the canvas. ----The word gesso is a noun, but many artists also use it as a verb. For example: "You need to gesso your canvas before you paint."


Lime powder and gesso were the first whites available in prehistoric times. However the most important contribution to art materials from Greece was lead white used since about the 4rth century BCE, a pigment that would become ubiquitous in Western art. To make their paint, artists would grind a lead brick into a powder (highly toxic) and while getting their lovely paint would occasionally develop painter's colic.


Lead white oil paint is made by grinding basic lead carbonate (the chemical name for lead white pigment) in vegetable drying oil. Normal lead carbonate (PbCO3) or other lead carbonate compounds have at times been mistakenly identified as basic lead carbonate, which has the chemical formula 2PbCO3•Pb(OH)2. The other varieties of lead carbonate have not been reported in paintings, except as impurities. Basic lead carbonate contains from 25 to 30 percent lead hydroxide, which distinguishes it from normal lead carbonate. It is this element that gives added opacity to lead white. It also gives it the qualities in oil paint often sought after by artists.


The process for making lead white paint is called the “stack process” or the old Dutch process. Imagine putting lead flakes in a lovely mix of heated strong vinegar and a gas of rotting horse manure or the off-gassing of fermentables. First you will get lead acetate in this process which then decomposes to lead carbonate. 

In the city of Klagenfurt Austria, a superior lead was mined from the Krems Galena mines and this lead resulted in the whitest white, now referred to as Krems white. 


From the smithsonian website:

In 2018, researchers in the United States discovered titanium white in 400-plus-year-old ceremonial wooden drinking cups made by the Inca and residing today in various museums. Carved with elaborate geometrical designs, the cups, called qeros, traditionally were not colored. But around the time of the Spanish conquest of Peru in 1530, the Inca started mixing pigments, including titanium white, into resin and decorating qeros with the bright goo.

The question remains that modern pigments based on titanium and zinc didnt come around until centuries later. How did the Inca jump 400 years into the future?


Giacomo Deposit, an unusual mineral sand deposit near the border between modern Chile and Peru that’s full of naturally occurring titanium dioxide and silica with a quality close to but not quite as white as today's modern white paints.

However by 1570, the Inca had stopped using titanium dioxide. Incan craftspeople eventually switched to lead white, which the conquistadors brought from Europe.


Other versions of white include Lipothone (Barium Sulphate and Zinc Sulphide), first created in the 1870s was the first modern white not made of lead and by 1928 it held 60% of the market for white pigments, rivaling both Lead White and Zinc White. By 1945 this demand had decreased to 15% due to the popularity and low cost of Titanium White. 


First discovered in 1908 at Niagara Falls NY by Auguste Rossi  and introduced in 1921, Titanium White (Titanium Dioxide) now dominates the white pigment market. More than five million tons of Titanium White are used every year in the production of plastics, cosmetics, paper, medicines, house paints, and artist paints. Titanium White is very opaque and extremely strong in mixtures.


So, useful information: if you own a white car you can expect up to 20% lower temperature within the car on a hot summer day with an interior temperature that can reach 57C 135F on a 35C 95F day.


White in Fashion


White was an enduringly fashionable color for both men and women into the 18th and 19th centuries, with a cultural fascination for Ancient Greece and Rome helping to prolong its popularity.


Although historically some famous brides did opt for white gowns on their wedding day, such as Mary, Queen of Scots, when she married her first husband, Francis Dauphin of France, in 1559, it wasn’t until Queen Victoria chose to wear a white court dress at her wedding to Prince Albert in 1840 that the trend for white bridal dresses became commonplace across the Western world.



Purple

  • So first things first, what is the difference between purple and violet.

  • Violet is a color on the spectrum of visible light - wavelength between 380 - 420 nm (spectral range)

  • Purple - combination of red and blue on the spectrum - mixture of single wavelengths

  • So how can we get purple pigment

  • Mix hematite and manganese 

  • Early cave paintings in Pech Merle in France dating from 25,000 - 16,000 BCE

  • Hematite - name from the Greek word for blood (haima) because of red coloration

  • Fe2O3 (iron oxide)

  • Widely found in rocks and soils

  • Same crystal structure a corundum (which we covered earlier - sapphire)

  • Naturally - black to steel gray to brown or reddish-brown, red

  • Electrically conductive 

  • Ochre clay is colored by varying amounts of hematite and is/was a popular natural pigment

  • Manganese - chemical element Mn

  • Hard, brittle, silvery metal often found with iron

  • Second most abundant transition metal in the earth’s crust

  • Found in trace amounts in humans where it it’s involved in bone formation and free radical defense

  • It reacts with iron to reduce strong green color in glass and larger quantities are used to make pink glass

  • It was one of the compounds used to make YInMn - the new blue we talked about last episode

  • So that’s a lot of science, how about a story:

  • Say you’re walking on a Mediterranean beach with your dog and the dog is digging in the seashells, as they do and you look over and there’s all this dark color staining your dog’s mouth.  You run over to investigate thinking it’s blood, and find instead a dark purple dye.  And then imagine you are the mythic hero Hercules.  What would you do? Why you make it one of the most sought after dyes in history, spawning the lastly connection between purple and royalty and then have that moment immortalized in a painting by Ruben (on our Instagram)

  •  A slight more likely story was that it wasn’t Hercules the mythic warrior but Heracles of Tyre, a philosopher

  • What is true about that story is the a popular and rare purple dye, Tyrian purple did come from a snail.  (for reference, Tyre was in Ancient Phoenicia, which is today in Lebanon)

  • The snail which produced this amazing color is called Bolinus brandaris (which in Instagram)

  • It’s a predatory sea snail - lives in central and western parts of the Mediterranean and occasionally in the Indian Ocean and South China Sea

  • It is edible

  • It produces a milky white mucus from its hypobranchial glands, which turns a deep reddish purple when exposed to the air and this is what was used for the dye

  • However, it took a lot of snails to produced enough dye for fabric so that is why the color was reserved for royalty and/or those who could pay for it

  • Interestingly, in ancient China, purple dye was not made from snails but from purple gromwell, plant but it didn’t adhere well to fabrics

  • It is thought that the Chinese were the first to develop synthetic purple dye but using barium copper, silicon and oxygen and it’s more of an indigo - being really dark blue

  • The Han purple then decomposes and copper oxide is formed, which adds red to the color, making it purple

  • Take barium mineral, quartz and a copper mineral and a lead salt and it was heated to around 900-1000 C

  • Though this sounds like Egyptian Blue - there is little evidence that they came from each other

  • As seems to be a pattern with pigments, synthetic purple was discovered when a scientists was trying to invent something else.  In 1856, William H Perkin was experimenting to try and make synthetic quinine to treat malaria.  Instead he found a synthetic purple dye that quickly dominated the market, especially after Queen Victoria wore it. It was called mauveine

  • Oddly, it wasn’t used much after the mid 1860s, except for on stamps

  • By examining samples from museums, scientists have been able to recreate the original mauveine

  • They found more than 13 different methyl derivatives of 7-amino-5-phenyl-3-(phenylamino)phenazin-5-ium compounds

  • Methyl derivatives are the addition of different numbers of methyl groups, which are a C surrounded by 3 Hs

  • The derivatives have absorption maxima in the 540-550 nm range (purple)

  • In a full circle moment, one of the modern purple pigments is called Manganese violet

  • Ammonium manganese pyrophosphate

  • Inorganic compound that you prepare by heating manganese oxide, diammonium phosphate and phosphoric acid

  • Used in eye liner, eye shadow, lipstick, nail polish and oil paint


Glossary:

  • Hematite

  • Manganese

  • Methyl group


Fun Party Facts

  • How was tyrian purple discovered

  • What element is in ancient and modern purple dyes


Thank you again for listening to this season premiere 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 our Youtube channel a follow since we’ve been posting weekly cocktails and science discussions (Science Sips), some videos from around Greece and our LuxeSci Field trips


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