![]() If we use lots of talc, dolomite or another source of magnesium in a cobalt glaze, a beautiful bubble-gum purple glaze can be the result! Magnesium oxide (MgO) shifts the wavelengths of light emitted from our fired cobalt glaze from blue to purple. Very dependable color results in both oxidation and reduction conditions, and in fast and slow firing.Atmosphere and firing temperature do not change the color.Very fine particle size, gives more uniform color in glazes.Soluble in glaze melt, thus it has little or no opacifying effect.Strongest coloring oxide: 0.25% noticeably blue in a transparent base glaze, used in a wide array of decal inks, underglaze colors, body stains, and colored glazes.CoO and Co3O4, although mainly thought of as colorants, are also strong fluxes.Cobalt Carbonate: Co3O4 (mix of CoO and Co2O3).Cobalt Oxide: CoO is 1.4 times stronger than cobalt carbonate.Because the glass formed in the glaze firing controls the interaction of the glaze elements, what you see in the mixed glaze is almost never the color you get in the fired glaze. That is why we may add both cobalt (blue) and chrome (green) to get a glaze that is turquoise.įlux elements such as sodium, stabilizers such as alumina, and even some glass formers also influence valence electrons. The interaction between atoms of one colorant, say cobalt, and another, say chrome, alters the energy level of the valence electrons of both elements. However, two or more colorants in a glaze interact so that the wavelengths of light absorbed are different for the combination than for either colorant by itself. Cobalt in a fired glaze usually absorbs all wavelengths of visible light except blue and this is why a cobalt blue glaze is blue. Emit only one wavelength and you have that color, just like taking a little slice out of a rainbow. The energy level of the valence electrons determines which photons it will absorb (absorb them all and you have black) or emit (emit them all and you have white). When a fired glaze is exposed to light, the color of the glaze will depend entirely on which wavelengths of the light are absorbed by the valence electrons in the glaze colorants. This unit is used in unity molecular formulas for glazes.Ĭobalt Blue Glaze Recipes - Like a Slice From a Rainbow Mole: The base unit of measure for the amount of substance, either atoms or molecules. Valence Electrons: The unbound, shared electrons that move among atoms rather than moving within a single atom. ![]() When fired, the carbonate breaks down and CO2 goes up the chimney, leaving behind an oxide. In a glaze firing the oxygen usually comes from air, though in a fuel-fired kiln it may also come from carbon monoxide and carbon dioxide.Ĭarbonate: The compound of carbon and oxygen in a 1:3 ratio that gives a negatively charged ion. Some raw materials are used in oxide form (like black cobalt oxide) while others form oxides during the firing process. Oxides result when an element combines with oxygen. Oxide: A chemical compound containing at least one oxygen atom as well as at least one other element. There are four major factors that can affect a glaze’s color: the clay and slip beneath it, kiln atmosphere, fired temperature, and the glaze composition, including the colorants. Plus he shares some sweet cobalt blue glaze recipes. In this post, an excerpt from the “Technofile” department in Ceramics Monthly, Dave Finkelnburg discusses the many possibilities that are possible with this multifaceted little colorant. This colorant is actually quite versatile and can make glazes that run the gamut from green to purple, pink to blue violet, blues mottled with red, pink, and even an intense black. And what's not to love about that? But blue is not the only color cobalt produces. Pottery Making Illustrated Submission GuidelinesĬobalt blue glaze recipes are in most potters' repertoires because they produce beautiful blue glazes.Pottery Making Illustrated's Print Mailing Schedule.Ceramics Monthly's Print Mailing Schedule.Workhouse Clay International ICAN Merit Award.ICAN Making a Difference in Ceramics Award.Annual National K-12 Ceramic Exhibition Award.
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