Editing Ultramarine (section)

== Production ==
=== Natural production ===
[[Lapis lazuli]] stone was historically mined near [[Sar-i Sang|Sar-i-Sang]] in modern-day Afghanistan and traded to Mesopotamia and ancient Egypt as early as the third millennium BCE.<ref>{{Cite book |last=Naweed |first=Hamid |url=https://books.google.com/books?id=VXFXSpIY7pcC&vq |title=Art Through the Ages in Afghanistan |date=28 Feb 2013 |publisher=Author House |isbn=9781481742757 |pages=45-46}}</ref>  

A method to produce ultramarine from lapis lazuli was introduced by the 5th century for use in Buddhist cave temples.<ref>{{Cite web |date=2017-11-20 |title=Afghanistan’s Beautiful Link to Da Vinci’s $450 Million ‘Salvator Mundi’ |url=https://www.huffpost.com/entry/afghanistans-beautiful-link-to-da-vincis-450-million_b_5a132ac0e4b010527d677f42 |access-date=2025-02-02 |website=HuffPost |language=en}}</ref> The method was described by [[Cennino Cennini]] in the 15th century. This process consisted of grinding the lapis lazuli mineral, mixing the ground material with melted [[wax]], [[resin]]s, and [[oil]]s, wrapping the resulting mass in a cloth, and then kneading it in a dilute lye solution, a [[potassium carbonate]] solution prepared by combining [[wood ash]] with water. The blue lazurite particles collect at the bottom of the pot, while the colorless crystalline material and other impurities remain at the top. This process was performed at least three times, with each successive extraction generating a lower quality material. The final extraction, consisting largely of colorless material as well as a few blue particles, brings forth ultramarine ash which is prized as a [[Glaze (painting technique)|glaze]] for its pale blue transparency.<ref>Lara Broecke, ''Cennino Cennini's ''Il Libro dell'Arte'': a New English Translation and Commentary with Italian Transcription'', Archetype 2015, pp. 89–90.</ref> This extensive process was specific to ultramarine because the mineral from which it is derived has a combination of both blue and colorless pigments. If an artist were to simply grind and wash lapis lazuli, the resulting powder would be a greyish-blue color that lacks purity and depth of color since lapis lazuli contains a high proportion of colorless material.<ref>{{Cite journal |last=Plesters |first=Joyce |date=1966 |title=Ultramarine Blue, Natural and Artificial |url=https://www.jstor.org/stable/1505446 |journal=Studies in Conservation |volume=11 |issue=2 |pages=62–91 |doi=10.2307/1505446 |jstor=1505446 |issn=0039-3630}}</ref>

Although the lapis lazuli stone itself is relatively inexpensive, the lengthy process of pulverizing, sifting, and washing to produce ultramarine makes the natural pigment quite valuable and roughly ten times more expensive than the stone it comes from. The high cost of the imported raw material and the long laborious process of extraction combined has been said to make high-quality ultramarine as expensive as [[gold]].<ref name="Ashok-39" /><ref name="Plesters-1966-64" />

=== Synthetic production ===
In 1990, an estimated 20,000 tons of ultramarine were produced industrially. The raw materials used in the manufacture of synthetic ultramarine are the following:
* white [[kaolin]],
* [[anhydrous]] [[sodium sulfate]] (Na<sub>2</sub>SO<sub>4</sub>),
* anhydrous [[sodium carbonate]] (Na<sub>2</sub>CO<sub>3</sub>),
* powdered [[sulfur]],
* powdered [[charcoal]] or relatively ash-free [[coal]], or [[colophony]] in lumps.<ref name="EB19112">{{EB1911|inline=1|wstitle=Ultramarine}}</ref>

The preparation is typically made in steps:
* The first part of the process takes place at 700 to 750&nbsp;°C in a closed [[Furnace (central heating)|furnace]], so that sulfur, carbon and organic substances give reducing conditions. This yields a yellow-green product sometimes used as a pigment.
* In the second step, air or sulfur dioxide at 350 to 450&nbsp;°C is used to oxidize sulfide in the intermediate product to S<sub>2</sub> and S<sub>''n''</sub> [[chromophore]] molecules, resulting in the blue (or purple, pink or red) pigment.<ref>{{cite web |title=Manufacture of ultramarine |url=http://www.freepatentsonline.com/2441952.pdf |website=www.freepatentsonline.com}}</ref>
* The mixture is heated in a [[kiln]], sometimes in brick-sized amounts.
* The resultant solids are then ground and washed, as is the case in any other insoluble pigment's manufacturing process; the chemical reaction produces large amounts of [[sulfur dioxide]]. ([[Flue-gas desulfurization]] is thus essential to its manufacture where SO<sub>2</sub> pollution is regulated.)

Ultramarine poor in [[Silicon dioxide|silica]] is obtained by fusing a mixture of soft clay, sodium sulfate, charcoal, sodium carbonate, and sulfur. The product is at first white, but soon turns green "green ultramarine" when it is mixed with sulfur and heated. The sulfur burns, and a fine blue pigment is obtained. Ultramarine rich in silica is generally obtained by heating a mixture of pure clay, very fine white [[sand]], sulfur, and charcoal in a [[muffle furnace]]. A blue product is obtained at once, but a red tinge often results. The different ultramarines—[[green]], [[blue]], [[red]], and [[Violet (color)|violet]]—are finely ground and washed with water.<ref name="EB19112" />

Synthetic ultramarine is a more vivid blue than natural ultramarine, since the particles in synthetic ultramarine are smaller and more uniform than the particles in natural ultramarine and therefore [[Diffusion|diffuse]] light more evenly.<ref>{{Cite web |title=Ultramarine-Blue-Pigment – Analysis, Applications, Process, Patent, Consultants, Company Profiles, Suppliers, Market, Report |url=http://www.primaryinfo.com/projects/ultramarine-blue-pigment.htm |access-date=2018-10-11 |website=www.primaryinfo.com}}</ref> Its color is unaffected by light nor by contact with oil or lime as used in painting. [[Hydrochloric acid]] immediately bleaches it with liberation of [[hydrogen sulfide]]. Even a small addition of [[zinc oxide]] to the reddish varieties especially causes a considerable diminution in the intensity of the color.<ref name="EB19112" /> Modern, synthetic ultramarine blue is a non-toxic, soft pigment that does not need much mulling to disperse into a paint formulation.<ref>{{Cite journal |last=Patterson |first=Steven |title=The History of Blue Pigments in the Fine Arts: Painting, From the Perspective of a Paint Maker |url=https://royalsoc.org.au/images/pdf/journal/153-2-04Patterson.pdf |journal=Journal & Proceedings of the Royal Society of New South Wales |volume=153 |page=173}}</ref><gallery mode="packed" heights="150px">
File:Lapis-lazuli_hg.jpg|[[Lapis lazuli]] specimen (rough), Afghanistan
File:Natural_ultramarine_pigment.jpg|Natural ultramarine
File:Ultramarinepigment.jpg|Synthetic ultramarine blue
File:Pigment_Violet_15.jpg|Synthetic ultramarine violet
</gallery>