When you open a new package of clay, or it's summer and temperatures fluctuate, polymer clay can become too white to work with (cuts poorly, fingerprints, warps when moved to the cooktop). In that case you can stretch it out in the usual way and park it between two sheets of common white paper. The paper will absorb the surplus of solvents and will take the necessary body to work. Another resource is to refrigerate it for a while before working or once extended, before cutting.