Though an accurate thermometer and careful temperature control are necessary for successful tempering, they aren’t sufficient. The art of tempering lies in recognizing when the chocolate has accumulated enough stable crystals to form a dense, hard network as it cools. Insufficient tempering time, or insufficient stirring, produce too few stable crystal seeds and undertempered chocolate, which will form some unstable crystals when it cools. Too much stirring or time produce too many or too large stable crystals and overtempered chocolate, in which individual crystals predominate over the joined network. Overtempered chocolate is stable, but it can seem coarse, crumbly rather than snappy, dull in appearance, and waxy in the mouth.