Editing Ultramarine (section)

=== 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>