Service manual
Firing Overglaze
Overglaze is decoration applied over fired glaze or pol
-
ished porcelain bisque. Overglazes include china paints,
gold, and luster, which fire from 022 to 014.
Load overglazed ware the same way you would load ce
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ramic glaze. Use stilts and make sure ware is not touching
other ware. Ware must be completely dry before firing.
China paints will crack or peel if applied heavily. Apply
several light coats instead, firing between each, until you get
the shade you want. Not all china paint colors reach maxi
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mum color saturation at the same temperature even when
fired on the same ware. So you must know which colors you
should fire first at higher temperatures to prevent burning
out the original colors in later firings. For example, reds ma
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ture at a lower temperature than other colors and are fired
after the other colors have been fired. Reds and yellows
should not be fired side by side. Colors also mature at a lower
temperature on ceramic pieces than on porcelain or hard
china. Check the overglaze manufacturer’s literature for the
cone to use with each color and type of ware.
Vent the kiln during the first hour of firing by placing a ½”
post under the kiln top. Allow kiln to cool to room tempera
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ture before opening the kiln.
Firing Low Fire Greenware
Low-fire greenware has a firing range from cone 06 to 02.
The greenware must be bone dry before firing. Otherwise, it
will crack or even explode in the kiln. Check for dryness by
touching to cheek or inside of wrist. Moist ware will be cold.
Low-fire greenware may be stacked so that it touches
each other. It can be loaded without stilts. Load pieces di-
rectly on the firebrick bottom.
Ware should be fired in the position in which it will be
used when finished, except for large pieces with flat, vertical
surfaces such as wall plaques and clocks. These should be
fired flat to prevent warping. Pieces to be used together
should be fired in place, such as a box with its lid, to ensure a
good fit.
Low-fire greenware firing is simple. Just be certain the
greenware is fired to the pyrometric cone recommended by
the clay supplier. If the greenware is not fired hot enough,
the piece will absorb moisture after it has been glaze-fired
causing the glazed surface to crack. This is called “crazing,”
and is most often due to underfired greenware. To help
eliminate crazing, fire greenware at least one cone hotter
than glaze, and even hotter if glaze can still be applied easily
to the hard bisque. While glaze may be applied to greenware
and fired once, separate firings produce better quality, so we
do not recommend single firing of greenware and glaze.
Vent the kiln during the first hour of firing by placing a ½”
post under the top. Allow kiln to cool to room temperature
before opening.
12/
°F Temperature Equivalents For Orton
Self-Supporting Pyrometric Cones
Cone Self-Supporting Cones Pre-Fire
Number Color
Heated at: 27° F 108° F 270° F
Per Hour* Per Hour* Per Hour*
022 — 1087 1094 Green
021 — 1112 1143 Fuschia
020 — 1159 1180 Orange
019 1213 1252 1283 Yellow
018 1267 1319 1353 White
017 1301 1360 1405 Pink
016 1368 1422 1465 Light Blue
015 1382 1456 1504 Violet
014 1395 1485 1540 Gray
013 1485 1539 1582 Green
012 1549 1582 1620 Fuschia
011 1575 1607 1641 Orange
010 1636 1657 1679 Dark Red
09 1665 1688 1706 Dark Red
08 1692 1728 1753 Dark Red
07 1764 1789 1809 Dark Red
06 1798 1828 1855 Dark Red
05 1/2 1839 1859 1877 Dark Red
05 1870 1888 1911 Dark Red
04 1915 1945 1971 Dark Red
03 1960 1987 2019 Dark Red
02 1972 2016 2052 Dark Red
01 1999 2046 2080 Dark Red
1 2028 2079 2109 Dark Red
2 2034 2088 2127 Dark Red
3 2039 2106 2138 Dark Red
4 2086 2124 2161 Gray
5 2118 2167 2205 Green
5 1/2 2133 2197 2237 White
6 2165 2232 2269 Fuchsia
7 2194 2262 2295 Orange
8 2212 2280 2320 Yellow
9 2235 2300 2336 White
10 2284 2345 2381 Pink
*Rate of temperature increase during last 90 - 120
minutes of firing. Tables by courtesy of the Edward
Orton, Jr. Ceramic Foundation.