What is picking ?
Picking is the fracture of coating layer. It occurs when tack of the ink exceeds the cohesive forces of coating on to the base paper or the printing pressure is too high to pick the coating or the paper surface. Piling occurs if the paper coating is too sensitive to fountain solution and the coating dissolves and gets deposited on the blanket. If number of impressions / hr is high, coating material can build up rapidly and interfere with ink transfer. Piling is the result of the ink in the first units of the press, building tack on the surface of the paper and eventually causing paper failure on the blankets further down, in the press. Piling shows up immediately and is more concentrated at the tail of the print image. It can be controlled by increasing wet pick strength of coating and frequent wash-ups at the press.
