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Cr2O3 (Chrome Oxide)
|GSPT - Frit Softening Point
||2257-2427C (From The Oxide Handbook)|
Notes-Amphoteric chrome oxide is the only stable oxide of chromium metal and can be used at all temperatures to 1200C. This leaves a margin before it begins to volatilize around 1240C, the fumes are very toxic.
-Chromium is a 'fast' color, meaning it produces its characteristic green in slow or fast and oxidizing or reducing firing. It is also used in paints and dyes. The green color produced by chrome only is generally a drab army-helmet green.
-Chromium is used in the glass industry to make green glass (up to 1%). Antimony is sometimes used as a reducing agent to ensure an emerald green.
-Chromium is not very soluble in glass and does not form silicates or combine with fluxes readily unless compounds are finely ground (e.g. ball milled) and dispersed and amounts are not excessive (1% will dissolve in most glazes and give good color, but amounts above that are increasingly likely to opacify the glass rather than color it more, this is happening because it is not dissolving in the melt). Amounts up to 3% in a glaze recipe gives greyish green coloration.
-Zircon opacifier 1-2% is often added to chrome glazes to stabilize them and prevent brown edges.
-Chrome oxide can be used as a body stain in amounts to 5% to give grey-green.
-Drab chrome greens can be moved toward peacock green with the addition of cobalt oxide (1% each gives bright color). This works in boron and soda glazes.
-Chrome in zinc glazes tends to form brown zinc chromate.
-Because chrome reacts with normally inert tin to produce chrome-tin pink colors, calcium carbonate and alumina are usually used instead of tin to lighten and clarify chrome green glazes.
-Chrome-tin pinks are much more consistent if the combination is premelted (i.e. commercial stain) and if the glaze is high in calcium or strontium, and free of zinc. Strontium is most effective if a wide firing range is desired (0.1-0.5% chrome, 4-10% tin).
-Chromium oxide is added to enamels for green where borax and zinc are used to increase the brilliance of the color. However, chrome in ground coat enamels tends to react with the metal to cause blistering.
How do metal oxides compare in their degrees of melting?
Metallic oxides with 50% Ferro frit 3134 in crucibles at cone 6ox. Chrome and rutile have not melted, copper and cobalt are extremely active melters. Cobalt and copper have crystallized during cooling, manganese has formed an iridescent glass.
Chrome oxide powder
Ceramic Oxide Periodic Table in SVG Format
The periodic table of common ceramic oxides in scalable vector format (SVG). Try scaling this thumbnail: It will be crystal-clear no matter how large you zoom it.
All common pottery base glazes are made from only 11 elements (the grey boxes) plus oxygen. Materials decompose when glazes melt, sourcing these elements in oxide form; the kiln builds the glaze from these. The kiln does not care what material sources what oxide (unless the glaze is not melting completely). Each of these oxides contributes specific properties to the glass, so you can look at a formula and make a very good prediction of how it will fire. This is actually simpler than looking at glazes as recipes of hundreds of different materials.
Out Bound Links
In Bound Links
- (Oxides - Related)
CrO3 - Chromium Trioxide
By Tony Hansen
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