Pyrometric Cones and kiln temperatures

Cones and kiln temperatures. At Fired Art we use number 06 and 04 for our standard firings.

Cone
Number		 Fusion Temp.
C		 Colour
Scale		 Heat treatment range
022 605 Dull red Jewellers' enamels
021 615 Dull red Jewellers' enamels
020 650 Dull red Aluminium Melts (658C)
019 660 Dull red Potters' decorating kilns, Bright gold fire
018 720 Dull red  
017 770 Dull red
016 795 Dull red
015 805 Dull red
014 830 Dull red  
013 860 Dull red  
012 875 Dull red
011 905 Cherry red
010 895 Cherry red Common red clay products:
09 930 Cherry red bricks, drain tiles, flowerpots,
08 950 Cherry red soft roofing tiles, fire proofing.
07 990 Cherry red
06 1015 Orange
05 1040 Orange
04 1060 Orange
03 1115 Orange Shale & No. 2 fire clay products:
02 1125 Yellow Bricks, sewer lines, terra cotta,
01 1145 Yellow hard tiles for roofing and flooring,
1 1160 Yellow stoneware pottery and soft porcelain
2 1165 Yellow
3 1170 Yellow
4 1190 Yellow
5 1205 Yellow
6 1230 Yellow
7 1250 Yellow
8 1260 White
9 1285 White China, porcelain, abrasive wheels,
10 1305 White electrical porcelain,
11 1325 Brilliant white fire bricks
12 1335 Brilliant white
13 1350 Brilliant white
14 1400 Brilliant white Spark plugs, 
15 1435 Brilliant white high tension electrical porcelain
16 1465 Brilliant white
17 1475 Brilliant white
18 1490 Brilliant white
19 1520 Brilliant white
20 1530 Dazzling white
23-42 for temperatures up to 2015C

When heated at 100C per hour.

The fusing point values given in the table above have only a relative or theoretical value, being a summarised outline of determinations made by the U.S. Bureau of Standards and are approximate values given to the nearest 5C from the average of many determinations; therefore, between any two cones there may be an error of 5C. The values apply only when the cones are heated in kilns where the gases are normally oxidising and free from oxides of sulphur. If the cones show a hardening of the surface because of exposure to kiln gases with lack of oxygen, small corrections must be made. Fusion of a cone is said to have been attained when the tip touches the base upon which the cone has been set.

From what been stated above it is evident that pyrometric cones are not intended as a means of measuring temperature. Their sole purpose is to serve as a guide in the firing of ceramic wares. Since both the cones and the wares are composed of ceramic materials they are similarly affected by variable conditions within the kiln, and are thus a more reliable guide for firing than any device which indicates only one of those variables, namely the temperature. When the cones behave erratically, they indicate abnormal kiln conditions which in many instances affect the ware unfavourably. Cones in series should go over seriatim otherwise something is wrong with the firing conditions. Although fusion temperatures of cones are affected by sulphur oxides and since the majority of ceramic wares are fired with sulphurous fuel, nevertheless it does not follow that cones are not satisfactory under these conditions. A factory selects by trial a cone which has a satisfactory end point for its ware and since all the cones used by it go through this sulphur treatment, so far as that factory is concerned all have practically the same relative end points.

Series Classification - The soft or decorating series begins with number 022, softening at dull red heat and runs through to number 011, the temperature range between numbers being approximately 30C. Of these, number 017 represents the temperature usually employed for liquid bright gold, and most overglaze colours for pottery and glass are made to work best at this heat. These cones contain lead and are quite sensitive to reducing gases; they should be used only in muffle kilns or where they cannot come in contact with flames. The low temperature series includes numbers 010 to 01 and is used chiefly for firing red burning clay products and soft glazes The intermediate temperature series includes numbers 1 to 20 and is used chiefly for firing buff and white clay products and hard glazes. The high temperature series includes numbers 23 to 42 and is used chiefly for firing and testing refractory materials.

This information is from 'The Standard Pyrometric Cone Co. Columbus'.