PORCELAIN CLAYS

Miscellaneous

Family: Clay Other
Region: None
Mined At: Unspecified
Raw Mineral: Yes
Generic: No

Notes

(Richard Willis)

Unlike earthenware and stoneware, there are no “natural” porcelain clays. Porcelain clays came into being, and continue to be made, by adding pegmatite and kaolin to finely grained earthenware clays. Refining the process, it is normal to define traditional tableware and sculptural porcelains in terms of their varying proportions of feldspar, kaolin and a natural clay (selected for temperature, particle size and handling). Special (usually very high-fire) porcelains often supplement or replace the kaolin with talc or other refractories. In one precising sense, many maintain that in order to be called “porcelain” a clay must be capable of being fired to translucence before its melting point. see porcelain in PART I
composition profiles of porcelain clay “classics” (1040-1450ªC)
Chinese, c.1650AD — SiO₂72, Al₂O₃20, CaO 0.7, K₂O 5.7, Na₂O 0.5, traces 1.1
Japanese, c.1700AD — SiO₂ 74, Al₂O₃19, CaO 0.5, K₂O 5.0, Na₂O 0.4, traces 1.3Böttger, c.1715AD — SiO₂ 61, Al₂O₃33, CaO 4.8, K₂O 0.1, Na₂O 0.2, traces 0.9
Meissen, c.1731AD — SiO₂59, Al₂O₃35, CaO 0.3, K₂O 4.0, Na₂O 0.8, traces 0.9
Meissen, c.1965AD — SiO₂57.7, Al₂O₃29.9, CaO 0.56, K₂O 2.75, Na₂O 0.6, traces 8.48
Nymphenburg — SiO₂72.8, Al₂O₃18.4, Fe₂O₃ 2.5, CaO 3.3, MgO 0.3, K₂O 0.7, Na₂O 1.8, traces
Limoges — SiO₂70.2, Al₂O₃24, Fe₂O₃ 0.7, CaO 0.7, MgO 0.1, K₂O 4.3, traces
Sèvres — SiO₂70.8, Al₂O₃22.6, TiO₂1.1, CaO 0.5, xMgO 2.3, K₂O 2.1, traces
Berlin — SiO₂66.6, Al₂O₃28, Fe₂O₃ 0.7, CaO 0.7, MgO 0.6, K₂O 3.4, traces
Norton bone-china — SiO₂30.4, Al₂O₃13.1, Fe₂O₃ 0.3, TiO₂ 0.02, CaO 27.7, MgO 0.05, Na₂O 0.74, traces (+ 20.9 of P₂O₃)
“common” porcelain clay
St. Ives: 1200ºC – 25% feldspar, 45% kaolin, 16.6% ball clay, 13.3% quartz
ParosL 1150-1200ºC – 66.66% feldspar, 33.33% kaolin
Norton: 1150-1170ºC – 60% pot. feldspar, 30% kaolin, 10% ball clay
Artigas: 1300ºC – pegmatite 56, kaolin 44; sod/pot feldspar 45, silica 10, kaolin 45
“bone china” clay
Strode: 6 parts calcinated bone, 4 parts feldspar, 3.5 parts kaolin
Searle: 45% bone ash, 26% kaolin, 3% flint, 26% Cornwall
“Standard English”: 50% bone ash, 25% kaolin, 25% Cornwall
typical modern “soft” clay for 1040 – 1300ºC: kaolin 20-30%, feldspar 30-50%, quartz or sand added to bring total to 100%
typical modern “hard” clay for 1250 – 1450ºC: kaolin 40-60%, feldspar 30-50%, quartz or sand added to bring total to 100%
“talc” porcelain clay for 1300-1400ºC
steatite 87, pot. feld. 6, kaolin 7
steatite 60, kaaolin 15, mag. carb. 7.5, bar. carb. 17.5
steatite 88, kaolin 5, bar. carb. 6, cal. carb. 1
steatite 85, bar. carb. 9.5, bentonite 0.5, ball 5
“hard” porcelain clay in dry-weight parts, 1300ºC
elastic:kaolin 15, ball clay 30, sod/pot feld. 35, silica 20
casting slip: kaolin 25, ball clay 20, sod/pot feld. 35, silica 20,
casting slip; kaolin 15, ball clay 20, sod/pot feld. 25, alumina 40
casting slip; kaolin 20, ball clay 25, sod/pot feld. 35, alumina 20
“refractory” porcelain clay in dry-weight parts, 1350-1450ºC:
“Marquardt”: kaolin 65, sod/pot feld.1, flint 1.5, alum. hyd. 19
“alumina”: kaolin 10, alumina frit 90
“zircon”: kaolin 5, zircon 95
“beryllium”: kaolin 20, beryllium 80
“mullite”: kaolin 12, alum. hyd. 13, mullite grog 75

Authors

Richard Willis (Owner)

XML

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<material name="PORCELAIN CLAYS" descrip="" generic="0" rawmineral="1" searchkey="" loi="0.00">
<families>
<family name="Clay Other"/>
</families>
<notes>
<note>Unlike earthenware and stoneware, there are no &#147;natural&#148; porcelain clays. Porcelain clays came into being, and continue to be made, by adding pegmatite and kaolin to finely grained earthenware clays. Refining the process, it is normal to define traditional tableware and sculptural porcelains in terms of their varying proportions of feldspar, kaolin and a natural clay (selected for temperature, particle size and handling). Special (usually very high-fire) porcelains often supplement or replace the
kaolin with talc or other refractories. In one precising sense, many maintain that in order to be called &#147;porcelain&#148; a clay must be capable of being fired to translucence before its melting point. see porcelain in PART I 
composition profiles of porcelain clay &#147;classics&#148; (1040-1450&ordf;C) 
Chinese, c.1650AD &#151; SiO2 72, Al2O3 20, CaO 0.7, K2O 5.7, Na2O 0.5, traces 1.1 
Japanese, c.1700AD &#151; SiO2 74, Al2O3 19, CaO 0.5, K2O 5.0, Na2O 0.4, traces 1.3 
B&ouml;ttger, c.1715AD &#151; SiO2 61, Al2O3 33, CaO 4.8, K2O 0.1, Na2O 0.2, traces 0.9 
Meissen, c.1731AD &#151; SiO2 59, Al2O3 35, CaO 0.3, K2O 4.0, Na2O 0.8, traces 0.9 
Meissen, c.1965AD &#151; SiO2 57.7, Al2O3 29.9, CaO 0.56, K2O 2.75, Na2O 0.6, traces 8.48 
Nymphenburg &#151; SiO2 72.8, Al2O3 18.4, Fe2O3 2.5, CaO 3.3, MgO 0.3, K2O 0.7, Na2O 1.8, traces 
Limoges &#151; SiO2 70.2, Al2O3 24, Fe2O3 0.7, CaO 0.7, MgO 0.1, K2O 4.3, traces 
S&egrave;vres &#151; SiO2 70.8, Al2O3 22.6, TiO2 1.1, CaO 0.5, xMgO 2.3, K2O 2.1, traces 
Berlin &#151; SiO2 66.6, Al2O3 28, Fe2O3 0.7, CaO 0.7, MgO 0.6, K2O 3.4, traces 
Norton bone-china &#151; SiO2 30.4, Al2O3 13.1, Fe2O3 0.3, TiO2 0.02, CaO 27.7, MgO 0.05, Na2O 0.74, traces (+ 20.9 of P2O3) 
&#147;common&#148; porcelain clay 
 St. Ives: 1200&ordm;C &#150; 25% feldspar, 45% kaolin, 16.6% ball clay, 13.3% quartz 
ParosL 1150-1200&ordm;C &#150; 66.66% feldspar, 33.33% kaolin 
Norton: 1150-1170&ordm;C &#150; 60% pot. feldspar, 30% kaolin, 10% ball clay 
Artigas: 1300&ordm;C &#150; pegmatite 56, kaolin 44; sod/pot feldspar 45, silica 10, kaolin 45 
 &#147;bone china&#148; clay 
Strode: 6 parts calcinated bone, 4 parts feldspar, 3.5 parts kaolin 
Searle: 45% bone ash, 26% kaolin, 3% flint, 26% Cornwall 
&#147;Standard English&#148;: 50% bone ash, 25% kaolin, 25% Cornwall 
typical modern &#147;soft&#148; clay for 1040 &#150; 1300&ordm;C: kaolin 20-30%, feldspar 30-50%, quartz or sand added to bring total to 100% 
typical modern &#147;hard&#148; clay for 1250 &#150; 1450&ordm;C: kaolin 40-60%, feldspar 30-50%, quartz or sand added to bring total to 100% 
&#147;talc&#148; porcelain clay for 1300-1400&ordm;C 
steatite 87, pot. feld. 6, kaolin 7 
steatite 60, kaaolin 15, mag. carb. 7.5, bar. carb. 17.5 
steatite 88, kaolin 5, bar. carb. 6, cal. carb. 1 
steatite 85, bar. carb. 9.5, bentonite 0.5, ball 5 
&#147;hard&#148; porcelain clay in dry-weight parts, 1300&ordm;C 
elastic:kaolin 15, ball clay 30, sod/pot feld. 35, silica 20 
casting slip: kaolin 25, ball clay 20, sod/pot feld. 35, silica 20, 
casting slip; kaolin 15, ball clay 20, sod/pot feld. 25, alumina 40 
casting slip; kaolin 20, ball clay 25, sod/pot feld. 35, alumina 20 
&#147;refractory&#148; porcelain clay in dry-weight parts, 1350-1450&ordm;C: 
&#147;Marquardt&#148;: kaolin 65, sod/pot feld.1, flint 1.5, alum. hyd. 19 
&#147;alumina&#148;: kaolin 10, alumina frit 90 
&#147;zircon&#148;: kaolin 5, zircon 95 
&#147;beryllium&#148;: kaolin 20, beryllium 80 
&#147;mullite&#148;: kaolin 12, alum. hyd. 13, mullite grog 75 

</note>
</notes>
</material>

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PORCELAIN CLAYS

Miscellaneous

Notes

(Richard Willis)

Authors

XML