Eutectics
A eutectic is where a mix of chemicals has a locally minimum melting point, i.e. increasing or decreasing the proportion of any of the substances will result in a higher melting point. In most cases, the melting point at the eutectic is lower than the melting point of any of the substances on their own.
Note that a mixture may have more than one eutectic, even if it is of just two components, as the eutectic is just a local minimum (i.e. whichever way you go from the eutectic, the melting point goes up), and not the global minimum (i.e. the lowest possible melting point). However the lowest possible melting point will occur at a eutectic.
As the proportions of components of a mixture are varied, in the solid state they fit together with different levels of ease, and different bond strengths between the components. A eutectic is a point where the bond strengths are at a minimum, and so it is easily melted.
You can read a bit more about eutectics in general on Wikipedia.
Table of Melting Points and Eutectics
The table below gives many eutectic points (in italics) and melting points of substances used by potters, up to 1300°C.
The table is sorted alphabetically based on the formula in additive mode. As an example, soda alumina silicate is given as Na2O·4.550 SiO2·0.185 Al2O3 - we order the molecules first by increasing number of atoms in each molecule, and when this is the same by alphabetical order. Note that older conventions for naming chemicals may place the molecules in a different order.
| Eutectic | Name | Composition by weight (%) | Melting point °C |
| KF | Potassium fluoride | 885 | |
| NaF | Sodium fluoride | 1040 | |
| CdO·SiO2 | Cadmium metasilicate | CdO 68.0, SiO2 32 | 1155 |
| KF·1.2 BaF2 | Potassium fluoride and barium fluoride | KF 78.7, BaF2 21.3 | 750 |
| NaF·2.1 PbF2 | Sodium fluoride and lead fluoride | NaF 7.8, PbF2 92.2 | 540 |
| MnS·13.3 MnSiO3 | Manganese sulfide and manganese metasilicate | MnO 51.5, MnS 4.7, SiO2 43.8 | 1130 |
| PbO·0.04 SiO2 | Lead oxide and silica | PbO 98.8, SiO2 1.2 | 540 |
| PbO·0.20 SiO2 | Lead oxide and silica | PbO 94.5, SiO2 5.5 | 526 |
| PbO·0.26 SiO2 | Lead oxide and silica | PbO 92.9, SiO2 7.1 | 508 |
| PbO·0.29 SiO2 | Lead oxide and silica | PbO 92.2, SiO2 7.8 | 560 |
| 3 PbO·SiO2 | Lead oxide and lead orthosilicate | PbO 91.7, SiO2 8.3 | 552 |
| 2 PbO·SiO2 | Lead orthosilicate | PbO 88.1, SiO2 11.9 | 746 |
| 3 PbO·2 SiO2 | Lead metasilicate and lead orthosilicate | PbO 84.7, SiO2 15.3 | 690 |
| PbO·SiO2 | Lead metasilicate | PbO 78.7, SiO2 21.3 | 770 |
| PbO·2.4 SiO2 | Lead oxide and silica | PbO 60.6, SiO2 39.4 | 661 |
| NaF·3.28 CaF2·3 AlF3 | Cryolite and fluorite | NaF 44.8, CaF2 25.4, AlF3 29.8 | 905 |
| BaO·4.0 SiO2·0.43 Al2O3 | Barium oxide, alumina and silica | BaO 35.0, SiO2 55.0, Al2O3 10.0 | 1200 |
| 2.5 BaO·2 SiO2·Al2O3 | Barium aluminium silicate and barium oxide | BaO 63.2, SiO2 19.9, Al2O3 16.9 | 1220 approx. |
| CaO·2 SiO2·Al2O3 | Anorthite | CaO 20.1, SiO2 43.3, Al2O3 36.6 | 1550 |
| CaO·2.48 SiO2·0.35 Al2O3 | Calcium - aluminium - silicate | CaO 23.25, SiO2 62.0, Al2O3 14.75 | 1170 |
| 2 FeO·2 SiO2·Al2O3 | Ferrous oxide and calcined kaolin | FeO 39.2, SiO2 33.0, Al2O3 27.8 | 1210 approx. |
| MgO·2 SiO2·0.392 Al2O3 | Magnesium oxide, alumina and silica | MgO 20.0, SiO2 60.0, Al2O3 20.0 | 1350 |
| 2 MgO·2 SiO2·Al2O3 | Magnesium oxide and calcined kaolin | MgO 26.6, SiO2 39.8, Al2O3 33.6 | 1330 approx. |
| 2 MnO·2 SiO2·Al2O3 | Manganese oxide and calcined kaolin | MnO 38.9, SiO2 33.1, Al2O3 28.0 | 1120 approx. |
| PbO·1.91 SiO2·0.254 Al2O3 | Lead - alumina - silica | PbO 61.2, SiO2 31.7, Al2O3 7.1 | 650 |
| PbO·0.78 SiO2·0.238 B2O3 | Lead oxide - boric oxide - silica | PbO 77.8, SiO2 16.4, B2O3 5.8 | 485 |
| 2.5 SrO·2 SiO2·Al2O3 | Strontium - aluminium - silicate and strontium oxide (SrO) | SrO 53.7, SiO2 25.1, Al2O3 21.2 | 1290 approx. |
| ZnO·0.9 SiO2·0.225 Al2O3 | Zinc oxide, alumina and silica | ZnO 51.3, SiO2 34.2, Al2O3 14.5 | 1360 |
| 3KF·AlF3 | Potassium cryolite | KF 50.9, AlF3 49.1 | 1035 |
| 3NaF·AlF3 | Cryolite | NaF 60, AlF3 40 | 998 |
| CaO·Fe2O3 | Calcium ferrite | CaO 26, Fe2O3 74 | 1203 |
| 0.91 CaO·0.09 Na2O·2.36 SiO2·Al2O3 | 1 Albite, 5 Anorthite | CaO 16.9, Na2O 1.9, SiO2 47.3, Al2O3 33.9 | Fuses 1465 - 1521 |
| 0.8 CaO·0.2 Na2O·2.8 SiO2·Al2O3 | 1 Albite, 2 Anorthite | CaO 13.7, Na2O 3.8, SiO2 51.3, Al2O3 31.2 | Fuses 1372 - 1490 |
| 0.67 CaO·0.33 Na2O·3.33 SiO2·Al2O3 | 1 Albite, 1 Anorthite | CaO 10.4, Na2O5.7, SiO2 55.6, Al2O3 28.3 | Fuses 1287 - 1450 |
| 0.5 CaO·0.5 Na2O·4 SiO2·Al2O3 | 2 Albite, 1 Anorthite | CaO 6.9, Na2O 7.7, SiO2 60.1, Al2O3 25.3 | Fuses 1205 - 1394 |
| 0.4 CaO·0.6 Na2O·4.4 SiO2·Al2O3 | 3 Albite, 1 Anorthite | CaO 5.2, Na2O 8.7, SiO2 62.2, Al2O3 23.9 | Fuses 1175 - 1362 |
| 0.2 CaO·0.8 Na2O·5.2 SiO2·Al2O3 | 8 Albite, 1 Anorthite | CaO 2.4, Na2O 10.5, SiO2 65.6, Al2O3 21.5 | 1265 |
| BaO·B2O3 | Barium metaborate | BaO 68.7, B2O3 31.3 | 1050 |
| BaO·0.64 B2O3 | Barium pyroborate and metaborate | BaO 77.4, B2O3 22.6 | 750 |
| 2 BaO·B2O3 | Barium pyroborate | BaO 81.4, B2O3 18.6 | Approx 1000 |
| 3 BaO·2 B2O3 | Barium orthoborate | BaO 86.8, B2O3 13.2 | > 1300 |
| CaO·2 B2O3 | Calcium biborate | CaO 28.6, B2O3 71.4 | Approx. 1025 |
| 2CaO·3 B2O3 | Calcium biborate and metaborate | CaO 34.8, B2O3 65.2 | Approx. 990 |
| CaO·B2O3 | Calcium metaborate | CaO 44.4, B2O3 55.6 | 1095 |
| CaO·0.83 B2O3 | Calcium pyroborate and metaborate | CaO 49.1, B2O3 50.9 | Approx. 1060 |
| 2CaO·B2O3 | Calcium pyroborate | CaO 61.5, B2O3 38.5 | Approx. 1215 |
| CdO·B2O3 | Cadmium metaborate | CdO 64.7, B2O3 35.3 | 875 |
| CuO·B2O3 | Cupric metaborate | CuO 53.2, B2O3 46.8 | Approx. 980 |
| MgO·B2O3 | Magnesium oxide and boric oxide | MgO 36.6, B2O3 63.4 | 988 |
| 2 MgO·B2O3 | Magnesium oxide and boric oxide | MgO 53.6, B2O3 46.4 | 1340 |
| 3 MgO·B2O3 | Magnesium oxide and boric oxide | MgO 63.5, B2O3 36.5 | 1366 |
| 4 PbO·B2O3 | Lead oxide and boric oxide | PbO 92.7, B2O3 7.3 | 565 |
| 2 PbO·B2O3 | Lead oxide and boric oxide | PbO 86.4, B2O3 13.6 | 497 |
| 2.303 PbO·B2O3 | Lead oxide and boric oxide | PbO 88, B2O3 12 | 493 |
| 5 PbO·4 B2O3 | Lead oxide and boric oxide | PbO 79.9, B2O3 20.1 | 548 |
| PbO·2 B2O3 | Lead oxide and boric oxide | PbO 61.4, B2O3 38.6 | 768 |
| SrO·2 B2O3 | Strontium biborate | SrO 42.5, B2O3 57.5 | Approx. 930 |
| SrO·1.58 B2O3 | Strontium biborate and metaborate | SrO 48.2, B2O3 51.8 | Approx. 890 |
| SrO·B2O3 | Strontium metaborate | SrO 59.7, B2O3 40.3 | 1100 |
| SrO·0.71 B2O3 | Strontium pyroborate and metaborate | SrO 67.6, B2O3 32.4 | 980 |
| 2 SrO·B2O3 | Strontium pyroborate | SrO 74.7, B2O3 25.3 | Approx 1115 |
| BaF2 | Barium fluoride | 1280 | |
| CaF2 | Fluorite | 1361 | |
| PbF2 | Lead fluoride | 855 | |
| 5 Cu2O·SiO2 | Cuprous oxide and silica | Cu2O 92.23, SiO2 7.77 | 1074 |
| 4 Cu2O·SiO2 | Cuprous oxide and silica | Cu2O 90.47, SiO2 9.53 | 1089 |
| 3 Cu2O·SiO2 | Cuprous oxide and silica | Cu2O 87.69, SiO2 12.31 | 1062 |
| 2 Cu2O·SiO2 | Cuprous oxide and silica | Cu2O 82.61, SiO2 17.39 | 1042 |
| Cu2O·SiO2 | Cuprous oxide and silica | Cu2O 70.36, SiO2 29.64 | 1048 |
| K2O·1.29 SiO2 | Potash - silica | K2O 55, SiO2 45 | 780 |
| K2O·7.43 SiO2 | Potash - silica | K2O 17.5, SiO2 82.5 | 880 |
| Li2O·SiO2 | Lithium metasilicate | Li2O 33.2, SiO2 66.8 | 1180 |
| Na2O·0.972 SiO2 | Soda - silica | Na2O 51.5, SiO2 48.5 | 830 |
| Na2O·SiO2 | Sodium metasilicate | Na2O 50.7, SiO2 49.3 | 1018 - 1056 |
| Na2O·4.579 SiO2 | Soda - silica | Na2O 18.4, SiO2 81.6 | 860 |
| Na2O·1.73 SiO2·1.29 B2O3 | Soda - boric oxide - silica | Na2O 24.2, SiO2 40.6, B2O3 35.2 | 790 |
| K2O·6 SiO2·Al2O3 | Orthoclase | K2O 16.9, SiO2 64.8, Al2O3 18.3 | 1220 |
| K2O·7.5 SiO2·Al2O3 | 2 Orthoclase, 3 silica | K2O 14.5, SiO2 69.8, Al2O3 15.7 | 1265 |
| K2O·8 SiO2·Al2O3 | 1 Orthoclase, 2 silica | K2O 13.8, SiO2 71.2, Al2O3 15.0 | 1285 |
| K2O·9 SiO2·Al2O3 | 1 Orthoclase, 3 silica | K2O 12.7, SiO2 73.5, Al2O3 13.8 | 1292 |
| K2O·12 SiO2·Al2O3 | 1 Orthoclase, 6 silica | K2O 10.2, SiO2 78.7, Al2O3 11.1 | 1317 |
| K2O·6.978 SiO2·0.276 Al2O3 | Potash alumina silicate | K2O 17.3, SiO2 77.5, Al2O3 5.2 | 870 |
| K2O·2.85 SiO2·2.11 B2O3 | Potash - boric oxide - silica | K2O 22.8, SiO2 41.5, B2O3 35.7 | 630 |
| Na2O·4.550 SiO2·0.185 Al2O3 | Soda alumina silicate | Na2O 17.8 SiO2 77.1, Al2O3 5.1 | 800 |
| Na2O·6 SiO2·Al2O3 | Albite | Na2O 11.8, SiO2 68.8, Al2O3 19.4 | Below 1200 |
| Na2O·2 SiO2·Al2O3 | Nepheline | Na2O 21.8, SiO2 42.4, Al2O3 35.8 | 1223 |
| 3 Cu2O·2 B2O3 | Cuprous sesquiborate | Cu2O 75.4, B2O3 24.6 | 950 - 1000 |
| KPO3·3.37 (KBO2) | Potassium metaborate and KPO3·KBO2 | K2O 45.7, B2O3 33.9, P2O5 20.4 | 770 |
| KPO3·KBO2 | Potassium metaborate and metphosphate | K2O 47.1, B2O3 17.5, P2O5 35.4 | 885 |
| 6.25KPO3·KBO2 | Potassium metaborate and KPO3·KBO2 | K2O 41.7, B2O3 4.3, P2O5 54.0 | 681 |
| Li2O·SiO2·4.66(Li2O·B2O3) | Lithium metasilicate and metaborate" | Li2O 30.9, SiO2 18.7, B2O3 50.4 | 802 |
| Na2O·SiO2·1.52(Na2O·B2O3) | Sodium metasilicate and metaborate" | Na2O 48.9, SiO2 27.1, B2O3 24.0 | 815 |
| CaF2·1.09 CaSiO3 | Calcium fluoride and calcium metasilicate | CaF2 38.1, CaO 29.8, SiO2 32.1 | 1130 |
| K2O·B2O3 | Potassium metaborate | K2O 57.4, B2O3 42.6 | 968 |
| Na2O·B2O3 | Sodium metaborate | Na2O 47.0, B2O3 53 | 965 |
| Na2O·2 B2O3 | Borax (anhydrous) | Na2O 30.7, B2O3 69.3 | 741 |
| K2O·B2O3·1.24 (Na2O·2 B2O3) | Potassium and sodium metaborates | K2O 28.7, Na2O 23.5, B2O3 47.8 | 855 |
| Li2O·B2O3·1.43 (Na2O·2 B2O3) | Lithium and sodium metaborates | Li2O 10.4, Na2O 30.7, B2O3 58.9 | 640 |
| Na2O·B2O3·Na2O·P2O5 | Sodium metaborate and sodium metaphosphate | Na2O 36.9, B2O3 20.8, P2O5 42.3 | 800 |
| K2O·P2O5 | Potassium metphosphate | K2O 39.9, P2O5 60.1 | 823 |
| Na2O·P2O5 | Sodium metaphosphate | Na2O 30.4, P2O5 69.9 | 610 |
| B2O3 | Boric oxide | 294 | |
| MnSiO3 | Manganese metasilicate (Rhodonite) | MnO 54, SiO2 46 | 1216 |
| CaSiO3·4 FeSiO3 | Calcium metasilicate and ferrous silicate | FeO 44.6, CaO 8.7, SiO2 32.1 | 1130 |
| CaSiO3·7 MnSiO3 | Calcium and manganese metasilicates | MnO 47.9, CaO 5.4, SiO2 46.7 | 1134 |
| 1.75 CdSiO3·ZnSiO3 | Cadmium and zinc metasilicates | ZnO 17.2, CdO 47.6, SiO2 35.2 | 1052 |
| BaSiO3·2.62 Na2SiO3 | Barium and sodium metasilicates | Na2O 30.4, BaO 28.7, SiO2 40.9 | 908 |
| CaSiO3·3.8 Na2SiO3 | Calcium and sodium metasilicates | Na2O 40.6, CaO 9.6, SiO2 49.8 | 932 |
| SrSiO3·5.33 Na2SiO3 | Strontium and sodium metasilicates | Na2O 40.5, SrO 12.6, SiO2 46.9 | 875 |
| CaO·Al2O3·2SiO2 2.275 (Na2O·Al2O3·2SiO2) | Calcium and sodium aluminium silicates | Na2O 15.6, CaO 5.8, SiO2 42.6, Al2O3 36 | 1130 |
| 0.42 KAlSi3O8·0.58 NaAlSi3O8 approx. | Orthoclase and albite | K2O 7.1, Na2O 6.8, SiO2 67.1, Al2O3 19.1 | 1160 approx. |
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