A glass-ceramic article comprises a petalite crystalline phase and a lithium silicate crystalline phase. The weight percentage of each of the petalite crystalline phase and the lithium silicate crystalline phase in the glass-ceramic article are greater than each of the weight percentages of other crystalline phases present in the glass-ceramic article. The glass-ceramic article has a transmittance color coordinate in the CIELAB color space of: L*=from 20 to 90; a*=from −20 to 40; and b*=from −60 to 60 for a CIE illuminant F02 under SCI UVC conditions. In some embodiments, the colorant is selected from the group consisting of TiO.sub.2, Fe.sub.2O.sub.3, NiO, Co.sub.3O.sub.4, MnO.sub.2, Cr.sub.2O.sub.3, CuO, Au, Ag, and V.sub.2O.sub.5.

A glass-ceramic article comprises a petalite crystalline phase and a lithium silicate crystalline phase. The weight percentage of each of the petalite crystalline phase and the lithium silicate crystalline phase in the glass-ceramic article are greater than each of the weight percentages of other crystalline phases present in the glass-ceramic article. The glass-ceramic article has a transmittance color coordinate in the CIELAB color space of: L*=from 20 to 90; a*=from −20 to 40; and b*=from −60 to 60 for a CIE illuminant F02 under SCI UVC conditions. In some embodiments, the colorant is selected from the group consisting of TiO.sub.2, Fe.sub.2O.sub.3, NiO, Co.sub.3O.sub.4, MnO.sub.2, Cr.sub.2O.sub.3, CuO, Au, Ag, and V.sub.2O.sub.5.

A colored glass article includes from 40 mol % to 70 mol % SiO.sub.2; from 8 mol % to 20 mol % Al.sub.2O.sub.3; from 1 mol % to 10 mol % B.sub.2O.sub.3; from 1 mol % to 20 mol % Li.sub.2O; from 1 mol % to 15 mol % Na.sub.2O; from 0 mol % to 8 mol % MgO; from 0 mol % to 5 mol % ZnO; and from 0.0005 mol % to 1 mol % Au. MgO+ZnO is from 0.1 mol % to 6 mol %.

A colored glass article includes from 40 mol % to 70 mol % SiO.sub.2; from 8 mol % to 20 mol % Al.sub.2O.sub.3; from 1 mol % to 10 mol % B.sub.2O.sub.3; from 1 mol % to 20 mol % Li.sub.2O; from 1 mol % to 15 mol % Na.sub.2O; from 0 mol % to 8 mol % MgO; from 0 mol % to 5 mol % ZnO; and from 0.0005 mol % to 1 mol % Au. MgO+ZnO is from 0.1 mol % to 6 mol %.

A heat-resistant synthetic jewelry material having a transparent, semitransparent or nontransparent composite nanocrystalline material on the basis of nanosized oxide and silicate crystalline phases. The material includes at least one of the following crystalline phases: spinel, quartz-like phases, sapphirine, enstatite, petalite-like phase, cordierite, willemite, zirconium, rutile, zirconium titanate, zirconium dioxide with a content of ions of transition elements, rare-earth elements and precious metals of from 0.001 to 4 mol %. One of the crystalline phases is additionally quartz-like solid solutions of lithium magnesium zinc aluminosilicates with a virgilite or keatite structure. The composition is selected from the following components,s SiO.sub.2, Al.sub.2O.sub.3, MgO, ZnO, Li.sub.2O, PbO, ZrO.sub.2, TiO.sub.2, NiO, CoO, CuO, Cr.sub.2O.sub.3, Bi.sub.2O.sub.3, Fe.sub.2O.sub.3, MnO.sub.2, CeO.sub.2, Nd.sub.2O.sub.3, Er.sub.2O.sub.3, Pr.sub.2O.sub.3 and Au.

A heat-resistant synthetic jewelry material having a transparent, semitransparent or nontransparent composite nanocrystalline material on the basis of nanosized oxide and silicate crystalline phases. The material includes at least one of the following crystalline phases: spinel, quartz-like phases, sapphirine, enstatite, petalite-like phase, cordierite, willemite, zirconium, rutile, zirconium titanate, zirconium dioxide with a content of ions of transition elements, rare-earth elements and precious metals of from 0.001 to 4 mol %. One of the crystalline phases is additionally quartz-like solid solutions of lithium magnesium zinc aluminosilicates with a virgilite or keatite structure. The composition is selected from the following components,s SiO.sub.2, Al.sub.2O.sub.3, MgO, ZnO, Li.sub.2O, PbO, ZrO.sub.2, TiO.sub.2, NiO, CoO, CuO, Cr.sub.2O.sub.3, Bi.sub.2O.sub.3, Fe.sub.2O.sub.3, MnO.sub.2, CeO.sub.2, Nd.sub.2O.sub.3, Er.sub.2O.sub.3, Pr.sub.2O.sub.3 and Au.

The invention provides a method for producing composite nanoparticles, the method using a first compound capable of transitioning from a monoclinic to a tetragonal rutile crystal state upon heating, and having the steps of subjecting the first compound to a hydrothermal synthesis to create anisotropic crystals of the compound; encapsulating the first compound with a second compound to create a core-shell construct; and annealing the construct as needed. Also provided is a device for continuously synthesizing composite nanoparticles, the device having a first precursor supply and a second precursor supply; a mixer to homogeneously combine the first precursor and second precursor to create a liquor; a first microreactor to subject the liquor to hydrothermic conditions to create an\isotropic particles in a continuous operation mode; and a second microreactor for coating the particles with a third precursor to create a core-shell construct.

The invention provides a method for producing composite nanoparticles, the method using a first compound capable of transitioning from a monoclinic to a tetragonal rutile crystal state upon heating, and having the steps of subjecting the first compound to a hydrothermal synthesis to create anisotropic crystals of the compound; encapsulating the first compound with a second compound to create a core-shell construct; and annealing the construct as needed. Also provided is a device for continuously synthesizing composite nanoparticles, the device having a first precursor supply and a second precursor supply; a mixer to homogeneously combine the first precursor and second precursor to create a liquor; a first microreactor to subject the liquor to hydrothermic conditions to create an\isotropic particles in a continuous operation mode; and a second microreactor for coating the particles with a third precursor to create a core-shell construct.

Glass-ceramics and precursor glasses that are crystallizable to glass-ceramics are disclosed. The glass-ceramics of one or more embodiments include rutile, anatase, armalcolite or a combination thereof as the predominant crystalline phase. Such glasses and glass-ceramics may include compositions of, in mole %: SiO.sub.2 in the range from about 45 to about 75; Al.sub.2O.sub.3 in the range from about 4 to about 25; P.sub.2O.sub.5 in the range from about 0 to about 10; MgO in the range from about 0 to about 8; R.sub.2O in the range from about 0 to about 33; ZnO in the range from about 0 to about 8; ZrO.sub.2 in the range from about 0 to about 4; B.sub.2O.sub.3 in the range from about 0 to about 12, and one or more nucleating agents in the range from about 0.5 to about 12. In some glass-ceramic articles, the total crystalline phase includes up to 20% by weight of the glass-ceramic article.

Glass-ceramics and precursor glasses that are crystallizable to glass-ceramics are disclosed. The glass-ceramics of one or more embodiments include rutile, anatase, armalcolite or a combination thereof as the predominant crystalline phase. Such glasses and glass-ceramics may include compositions of, in mole %: SiO.sub.2 in the range from about 45 to about 75; Al.sub.2O.sub.3 in the range from about 4 to about 25; P.sub.2O.sub.5 in the range from about 0 to about 10; MgO in the range from about 0 to about 8; R.sub.2O in the range from about 0 to about 33; ZnO in the range from about 0 to about 8; ZrO.sub.2 in the range from about 0 to about 4; B.sub.2O.sub.3 in the range from about 0 to about 12, and one or more nucleating agents in the range from about 0.5 to about 12. In some glass-ceramic articles, the total crystalline phase includes up to 20% by weight of the glass-ceramic article.