In ferroelectrics the domain structure in thin crystals is mostly determined by the surface impurities. In thick crystals of KNbO₃ with thickness greater than about 0.04 cm, however, domains are known to be formed through volume nucleation, and dislocations to play some role. The role of impurities must also be expected to be significant, especially when the elastic energy considerations are predominant in determining the domain configurations. On successive etching of thin flakes of thickness of about 0.02 cm obtained from the thick crystals of KNbO₃ by dilute HNO₃ a stage is found when a domain wall shows a series of black dots on it. Different walls show these dots at different stages of etching, and a wall may be 60 degrees as well as 90 degrees . Almost all the walls show this behaviour at one stage or the other indicating its general nature, and reasons are given to suggest that the dots may represent the impurity sites in the bulk. The etchant is also found to attack the regions near the domain wall selectively.