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03DSFF - Cone 03 Fast Fire
04DSDH - Low Temperature Drop-and-Hold
BQ1000 - Plainsman Electric Bisque Firing Schedule
BTFB04 - Bartlett Fast Bisque Cone 04
BTSG05 - Bartlett Slow Glaze Cone 05
C04PLTP - Plainsman Typical Cone 04
C10RPL - Plainsman Cone 10R Firing
C5DHSC - Plainsman Cone 5 Drop-and-Hold Slow-Cool
C6DHSC - Plainsman Cone 6 Slow Cool (Reactive glazes)
C6MSGL1 - Mastering Glazes Cone 6
C6PLST - Plainsman Cone 6 Electric Standard
FSCG1 - Shimbo Crystal Schedule 1
FSCGB1 - Bory 1 Fara Shimbo Crystalline Glaze
FSCGCL - Celestite
FSCGWM - Wollast-O-Matte Fara Shimbo Crystalline Glaze
FSCRGL - GC106 Base for Crystalline Glazes

FSHP2 - Shimbo Crystal Holding Pattern 2
FSHP3 - Shimbo Crystal Holding Pattern 3
FSNM5 - Fa's Number Five
PLC6CR - Cone 6 Crystal Glaze Plainsman
PLC6DS - Cone 6 Drop-and-Soak Firing Schedule

FSHP1 Firing Schedule

Shimbo Crystal Holding Pattern 1

The crystals in a crystalline glaze grow during the cooling cycle. As in nature, these crystals are the result of a slow cooling of a molten mass containing many chemicals, giving like molecules, moving through the melt, time to find each other and align in pattern, one by one. So the trick to growing crystals is to control cooling so that the optimum conditions exist for the crystals we want to grow. In our case, 'optimum' conditions are conditions of glaze viscosity. The glaze must be cool enough to allow zinc silicate molecules to lock into a position in the lattice, but warm enough to give them the mobility to find that position in the first place.

The temperature range at which zinc silicate crystals will grow in a glaze is said by some sources to be from 1180° to 1010° C (or about 2160° to 1850° F), and by others to be 1050° to 750° C (1922° to 1382° F). My own experience has been that my glazes will form crystals starting at about 160° C from peak temperature and will continue to do so within a range of about 70° C below that. Every new glaze should be tested carefully to see where its best crystal-growing range happens to be under your own firing conditions.

By choosing carefully the point at which you hold (or don't hold) your temperature, you can change the shape of the crystals you grow. At the high end, crystals tend to be acicular (needle-like). As the temperature is lowered through the growing range (something often referred to as a 'slant soak' the crystals 'fan out' and produce more variety of shape (as in Illustration 7.4). You can, if you like, hold your temperature at one point and get a crystal whose internal structure is very uniform, or allow the temperature to change and produce a more flower-like effect. Note also that the crystal color lightens as the temperature is lowered.

Step °C °F Hold Time
1 100°C/hr to 250C  180°F/hr to 482F  0 2:32  
2 250°C/hr to 500C  450°F/hr to 932F  0 3:32  
3 500°C/hr to 1221C  900°F/hr to 2229F  0 4:58  
4 999°C/hr to 1100C  1798°F/hr to 2012F  0 5:06  
5 100°C/hr to 1000C  180°F/hr to 1832F  0 6:06  
6 100°C/hr to 1050C  180°F/hr to 1922F  30min 7:06  
7 100°C/hr to 1020C  180°F/hr to 1868F  30min 7:54  
8 0°C/hr to 100C  0°F/hr to 212F  0 7:54  
Start temperature assumed: 25°C or 75°F
"Fahrenheit degrees" is not the same as "degrees Fahrenheit". A 100° reading on a Fahrenheit thermometer is equal to a 37° reading on a Celcius thermometer. But "100 Fahrenheit degrees of temperature change" is equivalent "55 Celsius degrees of change". That is an important distinction to understand the above temperature conversions.

Related Information


Firing Schedules Shimbo Crystal Holding Pattern 2
Electric firing: Crystal Glazes 2 by Fara Shimbo (page 138)
Typecodes Oxidation Firing

By Tony Hansen

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