Special anodizing process is the condition of several anodizing process that is done from several process of by certain company or from proprietary information available to licencess only. Anodizing condition process that is proposed based on licence are Martin Hard Coat (MHC), Aluminate 225 and 226, Alcanodox Hardas, Sandford, Kalcolor and Lasser.
Hard anodizing process uses a sulfuric acid bath containing 10 to 20% of acid, with or without additives. Operating condition temperature of the bath range from 0 to 10 oC, and with current density range between 2 and 3.6 A/dm2. By adding some additives and modifier for power, hard anodizing can be operated at higher temperature than room temperature. But hard anodizing that operate in higher temperature than room temperature may result soft formation and more porous outer layer. The change of character result will reduce wear resistance coating significantly and tends to limit coating thickness. If without use of some additives or modified power, such as superimposed alternating current over direct current or pulsed current, excessive operating temperatures result in dissolution of coating and can burnt and damage the work.
Prefer process condition that are commonly use solution containing 120 to 160 g of sulfuric acid and 12 to 20 g of oxalic acid per 3.8 lt water. Operating temperature at 10 + 1 oC and use current density of 2.5 to 3.6 A/dm2, voltage is increase gradually from zero to 40 or 60 V. Time treatment about 25 minute will result anodizing thickness about 1 mil or 25 micron.
For special condition process that mensioned above will use some parameter limitation as on the table below:
| Process Name | Bath | Temperature, oC | Duration, min | Voltage, volt | Current Density, A/dm3 |
| Martin Hard Coat (MHC) | 15% sulfuric acid, 85% water | - 4 to 0 | 45 (b) | 20 - 75 | 2.7 |
| Aluminate | 12% sulfuric acid, 1% oxalic acid, water | 10 | 20, 40 | 10 - 75 | 2.8 (b) |
| Alcanodox | Oxalic acid in water | 2 - 20 | (a) | (a) | (a) |
| Hardas | 6% Oxalic acid, 94% water | 4 | (a) | 60 DC plus AC overide | 2 |
| Sanford | Sulfuric acid with organic additives | 0 - 15 | (a) | 15 - 150 DC | 1.2 - 1.5 |
| Kalcolor | 7 - 15 % sulfosalicylic acid, 0.3-4 % sulfuric acid, water | 18 - 24 | ---- | ----- | 1.5 - 4 |
| Lasser | 0.75 % oxalic acid, 99.25 % water | 1 - 7 | to 20 | rising A 50 - 500 | V controlled |
b: change from last edition
