Editing Titanium dioxide (section)

===Pigment===
{{Main|Titanium white}}

First mass-produced in 1916,<ref>{{cite book|title=The Secret Lives of Colour|last=St. Clair|first=Kassia|publisher=John Murray|year=2016|isbn=978-1-4736-3081-9|location=London|page=40|oclc=936144129}}</ref> titanium dioxide is the most widely used white pigment because of its brightness and very high [[refractive index]], in which it is surpassed only by a few other materials (see ''[[list of indices of refraction]]''). Titanium dioxide crystal size is ideally around 220&nbsp;nm (measured by electron microscope) to optimize the maximum reflection of visible light. However, [[abnormal grain growth]] is often observed in titanium dioxide, particularly in its rutile phase.<ref name="ref1">{{cite journal| last1=Hanaor| first1=D. A. H. | last2=Xu| first2=W.|last3=Ferry|first3=M.|last4=Sorrell|first4=C. C. | title= Abnormal grain growth of rutile TiO<sub>2</sub> induced by ZrSiO<sub>4</sub>| journal= [[Journal of Crystal Growth]]| year= 2012| volume=359| pages=83–91| url= https://hal.archives-ouvertes.fr/hal-02315198/document/#page=2 | doi=10.1016/j.jcrysgro.2012.08.015|arxiv=1303.2761| bibcode=2012JCrGr.359...83H | s2cid=94096447 }}
</ref> The occurrence of abnormal grain growth brings about a deviation of a small number of crystallites from the mean crystal size and modifies the physical behaviour of TiO<sub>2</sub>. The optical properties of the finished pigment are highly sensitive to purity. As little as a few parts per million (ppm) of certain metals (Cr, V, Cu, Fe, Nb) can disturb the crystal lattice so much that the effect can be detected in quality control.<ref>{{Cite book |title=Kemira pigments quality titanium dioxide |last=Anderson |first=Bruce |year=1999 |location=Savannah, Georgia |pages=39}}</ref>{{Full citation needed|date=January 2025}} Approximately 4.6 million tons of pigmentary TiO<sub>2</sub> are used annually worldwide, and this number is expected to increase as use continues to rise.<ref name="Nano-scaled titania">{{cite book |last=Winkler |first=Jochen |title=Titanium Dioxide |year=2003 |isbn=978-3-87870-148-4 |pages=5 |publisher=Vincentz Network |location=Hannover, Germany}}</ref>

TiO<sub>2</sub> is also an effective [[opacifier]] in powder form, where it is employed as a pigment to provide whiteness and [[Opacity (optics)|opacity]] to products such as paints, coatings, plastics, papers, inks, foods, [[Dietary supplement|supplements]], medicines (i.e. pills and tablets), and most toothpastes; in 2019 it was present in two-thirds of toothpastes on the French market.<ref name=frouville>{{cite news |title=Deux dentifrices sur trois contiennent du dioxyde de titane, un colorant au possible effet cancérogène|language=fr|trans-title=Two out of three toothpastes contain titanium dioxide, a possibly carcinogenic colouring material|author=Margaux de Frouville|url=https://www.bfmtv.com/sante/deux-dentifrices-sur-trois-contiennent-du-dioxyde-de-titane-un-colorant-au-possible-effet-cancerogene-1660942.html |publisher=BFMTV.com |date=28 March 2019}}</ref> In paint, it is often referred to offhandedly as "brilliant white", "the perfect white", "the whitest white", or other similar terms. Opacity is improved by optimal sizing of the titanium dioxide particles.