|Monthly Tech-Tip |
Alternate Names: Fluorite, Calcium Fluoride, Blue John
CaF2 is used in frit preparation and as a low-fire enamel opacifier. It's value lies in the fact that it is an active flux and at the same time an opacifier.
At higher temperatures the fluorine becomes volatile and is released as a poisonous gas. This happens as O2 combines with CaF2 to produce CaO and F2 gas. Even if the gas can be tolerated, the material slowly decomposes to evolve the fluorine gas, and thus is troublesome for use in glazes because of the blistering problems.
If fluorspar is being used as a source of Ca at higher temperatures to create CaO oxide in a glass there has to be an oxidizing atmosphere in the kiln to supply the needed oxygen.
Fluorspars have varying amounts of iron contamination and can be very clean.
Opacifiers are powders that turn transparent glazes opaque by various chemical and physical mechanisms (and combinations of mechanisms).
Generic materials are those with no brand name. Normally they are theoretical, the chemistry portrays what a specimen would be if it had no contamination. Generic materials are helpful in educational situations where students need to study material theory (later they graduate to dealing with real world materials). They are also helpful where the chemistry of an actual material is not known. Often the accuracy of calculations is sufficient using generic materials.
Materials that source Na2O, K2O, Li2O, CaO, MgO and other fluxes but are not feldspars or frits. Remember that materials can be flux sources but also perform many other roles. For example, talc is a flux in high temperature glazes, but a matting agent in low temperatures ones. It can also be a flux, a filler and an expansion increaser in bodies.
Fluorspar at Wikipedia
Calcium Fluoride on Wikipedia
Can you be exposed to fluorine gas in ceramics. Yes, if you are using materials that contain fluorine. These are not many, but worth knowing about.
|Temperatures||Fluorspar melts (1330-)|
Questions and suggestions to help you reason out the real cause of ceramic glaze blistering and bubbling problems and work out a solution
|Oxides||F - Fluorine|
|Frit Softening Point||1330C M|
|Frit Softening Point||1370C|
|Density (Specific Gravity)||3.10|
|Glaze Surface Texture||Fluorspar generates gases that can produce vivid blistering for special purpose effects.|
|By Tony Hansen|
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