All properties of porcelain enamel frits are subject to modification through the selection of mill additions.
While the changes that are practical with mill addition variations can improve a marginal characteristic, usually there is not sufficient latitude in mill addition use to change a totally unsatisfactory property to a very satisfactory property.
Whenever it is impossible to produce satisfactory enamel characteristics through mill addition manipulations, changes in frit selection will be required.
Below an overview of typical enamel mill additions and their functions.
| Milling Addition | Function |
| Aerosil | for set-up |
| Aluminium oxide | matting agent and to increase heat resistance of ground coat |
| Aluminium hydroxide | equivalent to aluminium oxide |
| Aluminium powder | increase heat resistance in ground coat |
| Antimony trioxide | increase adherence of ground coat |
| Barium chloride | for set-up in cover coat |
| Barium carbonate | for set-up in cover coat |
| Bentonite | for set-up |
| Borax | for set-up in ground coat |
| Boric acid | for set-up |
| Cadmium oxide | to stabilise Cd-Se red enamels |
| Clay | provide bubble structure |
| Cupric chloride | for self lustre enamel 1118 |
| EK-1000 | for continuous clean enamel |
| Feldspar | for ground coat |
| Gumst | increase filmstrength |
| Magnesium chloride | for set-up cover coat |
| Magnesium nitrate | to increase suspension and to prevent fishscales |
| Opacifier UV | opacifier |
| Potash | for set-up |
| Potassium choride | for set-up cover coat |
| Potassium nitrate | oxidizing agent for aluminium enamels |
| Quartz | to increase firing range and matting agent |
| Silicic acid | for set-up |
| Silver sand | for heat resistant ground coat |
| Soda ash | for set-up in ground coat |
| Sodium aluminate | for set-up in cover coat |
| Sodium nitrite | for set-up in ground coat |
| Sodium pyrophosphate | to decrease set-up |
| Sodium silico fluoride | for set-up cover coat |
| Tinoxide | opacifier |
| Titanium dioxide | opacifier |
| Trisodium phosphate | to prevent rusting in cast iron ground coat |
| Urea | to prevent hairlines in cover coat |
| Zirconite | opacifier |
| Zircon oxide | opacifier |