•The secret to cool bodies and glazes is a lot of testing.
•The secret to know what to test is material and chemistry knowledge.
•The secret to learning from testing is documentation.
•The place to test, do the chemistry and document is an account at https://insight-live.com
•The place to get the knowledge is https://digitalfire.com
Hydrated Calcined Iron Oxide, Fe2O3, H2O, MnO2, SiO2
||If this formula is not unified correctly please contact us. |
Umber is a hydrated iron oxide that also contains significant manganese, calcia, alumina and silica. When umber is calcined (referred to as "burnt" because it is done to lower temperatures), the color intensifies. The material is used to color many products (e.g. for construction), in ceramics it is used to darken the fired color of clay bodies or engobes.
Burnt umber can be any of a variety of natural and synthetic iron oxides (there are many manufacturers and choices, this is because the coloring market for cement, for example, is so large and widespread). A variety of impurities are common. Some companies condition the color of their umbers by adding various colors of iron oxide.
Raw Umber vs. Burnt Umber
These are the same material, however the one on the right has been burnt to 600F. At this surprisingly low temperature the color transforms into a deep redish brown.
The covering power of an engobe is amazing. If they are not over-fluxed.
This cone 6 mug is made from a black clay (containing 10% burnt umber). The engobe on the inside is covered by a clear glaze. The color is the same as if the engobe were on a white or buff firing stoneware. Engobes get their covering power from the fact that they do not melt. If you see an engobe with lots of frit it will likely melt too much, be suspicious.
Out Bound Links
- (Suppliers - Manufacturer)
Whittaker Clark & Daniels Inc
1: CLT - Colorant
In Bound Links
XML for Import into INSIGHT
<?xml version="1.0" encoding="UTF-8"?>
<material name="Burnt Umber" descrip="Hydrated Calcined Iron Oxide, Fe2O3, H2O, MnO2, SiO2" searchkey="" loi="0.00" casnumber="12713-03-0">
<oxide symbol="CaO" name="Calcium Oxide, Calcia" status="" percent="3.500" tolerance=""/>
<oxide symbol="MgO" name="Magnesium Oxide, Magnesia" status="" percent="1.500" tolerance=""/>
<oxide symbol="Al2O3" name="Aluminum Oxide, Alumina" status="" percent="6.100" tolerance=""/>
<oxide symbol="SiO2" name="Silicon Dioxide, Silica" status="" percent="18.000" tolerance=""/>
<oxide symbol="Fe2O3" name="Iron Oxide, Ferric Oxide" status="" percent="54.000" tolerance=""/>
<oxide symbol="MnO" name="Manganous Oxide" status="" percent="11.500" tolerance=""/>
<volatile symbol="LOI" name="Loss on Ignition" percent="5.500" tolerance=""/>
Copyright 2003, 2008, 2015 https://digitalfire.com, All Rights Reserved