It is a good practice to stir plastisol inks before each use, due to the fact that plastisol inks will take on a thicker viscosity when it sits, even for just one day, let alone weeks. It is important to stir the plastisol before deciding whether or not to add viscosity reducers, because often the case is that printers add unnecessary viscosity reducers just because they didn’t stir the plastisol to break down the false body, namely the thicker viscosity. In case the plastisol ink has been sitting for a very long time, the clear liquid portion of the ink may separate from the heavier components of resin and pigment. No worries here, just stir.