**2.3.4 Preparation method**

Firstly, a suitable suspension of 2 g milled and sieved mica (20-60 µm) in 40 ml de-ionized water was prepared. The suspension pH was adjusted with dilute hydrochloric acid (5%) to pH which is shown in table 2.1 and then heated to desired temperature according to table 2.1 experiment plane. The mixture was heated up to desired temperature, then 0.0001 % (based on mica wt%) of nonionic surfactant (sorbitan mono-oleate ) was added to this suspension. Then, potassium chlorate aqueous solution (KClO3) was added to this suspension as an oxidizing agent.

According to the conditions shown in table 2.1, stirring rate, suspension temperature and pH were controlled. In order to coat the mica flake, SnCl2 solution and aluminium chloride (AlCl3) with a constant proportion SnCl2/AlCl3 = 9/1, were added to the mica suspension. The pH of the suspension was kept at desired level by addition of 3% aqueous sodium hydroxide solution. The coating process was stopped after the desired time. Then, the suspension was filtered and the prepared pigments were washed with distilled water until neutral pH was reached and dried at 100ºC. Finally the powders were calcined at 950ºC for 1h to get the pigment powders with pearlescent luster.
