On Magic Blue

              

lapis lazuli rock ( Wiki)

"The most perfect of all colors", thus wrote Cennino Cennini in the 15th century,  about   azzurre oltre marine in his   handbook for artists.  This mesmerising, precious  blue popularly known as ultramarine was  worth its weight in gold.  For Renaissance painters,  there were several   blue pigments to choose from  such as azure della magna, indigo, lapis armenus etc., but ultramarine  was the most sought after blue pigment.  The mineral rock  lapis lazuli from which the blue pigment was extracted, had to be imported from  beyond the seas and hence the name ultramarine.    Ancient caves dotting the Sar-i-Sang region in  Afghanistan were and are still the sole yet rich source of   Lapis lazuli. In old latin lapis means stone  and  lazuli is a derivative of lazulum,  a word associated with colour  blue. During there medieval times, rich patrons who commissioned paintings would often specify in the contract that ultramarine pigment must be used.  Because the  blue pigment prepared  from lapis lazuli retained brightness and clarity  for ages  whereas the cheaper  lapis armenus   turned green over time. Though comparatively costlier, ultramarine had  excellent spreading quality minute amounts were enough to paint the flowing robes of Virgin Mary or royalty or the vault of the  sky.

 Virgin Mary and infant Jesus 14th century
(wiki)

Lapis lazuli was known to the ancient world and they fashioned it easily into artefacts such as jewellery and decorative pieces.  But the process of  extracting  the blue pigment from the  rocks was laborious. Cennini in his  handbook  on the  art and science of painting and paint formulations, describes the process in detail. He cautions that for high quality pigment, blue rocks with minimal grey areas  must be selected and   ground dry to as fine a  powder  as possible.  The fine powder was then intimately mixed with 3 times  its weight of melted bees wax and   plant resins such as mastic and pine. The dough so obtained was kneaded repeatedly while being left to age for several days. Later when  extracted with very dilute aqueous alkali the pigment settled as a fine colloidal  paste. 

From alchemists, at the turn of the 19th century, chemists inherited the  spell of utramarine blue. It was known by then that the lazurite component of lapis lazuli held the blue.  An intense competitive search for a synthetic substitute began in 1824 when a competition was 

announced in France  with a prize money  of 6000 francs.  French chemist Jean-Baptiste Guimet and German professor of chemistry  Christian Gemlin  at the Tubingen University succeeded in freezing the correct composition. The prize however was awarded to Guimet.  Gemlin as sorely disappointed. Guimet chose to keep his formula secret, Gemlin published his results  and paved the  way for the ultramarine pigment industry. 

ultramarine blue structure
courtesy PubChem CID71587188

  While it was known that  sulphur content was responsible for the blue colour,  it took a century and half to  conclusively prove that the blue color is due to trisulfur  radical anion. 


The cheap synthetic substitute had no business to retain the name ultramarine, but it did and  pushed out  the original from the artists' palette almost  for ever.  

Tailpiece

In 2015, an art exhibition "Lapis Lazuli: The Magic of Blue" was held in Florence.  On display were artefacts and paintings of unique beauty, spanning from antiquity to the  21st century. 
In 2018, an international highway, Lapis lazuli corridor was inaugurated connecting Afghanistan to Turkey, reminiscent of the old trade route.

REFERENCES:
1. A treatise on painting : Cennini,Cennio
2. Lapis Lazuli and the history of the "Most Perfect Color"
3. Color in Art: a brief history of blue pigment.