i) Capping: There is partial or complete removal of top or bottom portion of the tablet. The reasons are: Excessive fines, defective punches and dies, high speed of the machine, too dry granules, or high degree of compaction.
ii) Picking and sticking: In picking, the material is removed or picked up by the upper punch from the upper surface of the tablet. In sticking, the material sticks to the wall of the die. These defects appear due to worn out dies and punches, small quantity of lubricants, presence of moisture in granules, excess powder in granules, scratches on the surface of face of punch or defects in the formulation.
iii) Mottling: Mottling means an unequal distribution of colour on the surface of coloured tablets. This defect occurs due to following reasons: migration of dye in the granules during drying, use of different colour of medicament and excipients.
iv) Weight variation: During compression of granules in a tablet machine, the tablets do not have a uniform weight. The reasons are: Granules not uniform in size, Excess powder in granules, no proper mixing of lubricants, no uniform flow of granules from hopper to die, variation in speed of machine.
v) Hardness variation: Causes same as weight variation. Hardness depends upon weight of material and space between upper and lower punches during compression. If any of these varies the hardness will vary.
vi) Double impression: This defect occurs when the lower punch has a monogram or some other engraving on it. During compression, the tablet receives an imprint on the punch. Due to some defect in the machine, the lower punch moves slightly upward before ejection of a tablet and gives a second though light imprint on the tablet.