Too much heat on the rod will soften it so that pressure cannot be maintained to push it into the base material. Insufficient heat on the rod will cause it to merely lie in the softened trough of base material without having fused to it. Both of these conditions, of course, mean an unsatisfactory weld. NOTE: A slight yellowing of the rod and base material is caused by slight overheating. This, however, is desirable during welding practice, to assure the beginner of having at least enough heat. It helps to eliminate the possibility of making cold welds. Once satisfactory welder manipulation is achieved, the beginner should gradually eliminate the yellowish tinge, but maintain the flow lines. Eventually, the beginner should produce cold welds intentionally in order to recognize them as such. They have no flow lines and minimum fusion takes place. This procedure should be repeated and alternated until the welder can rapidly from a cold weld or a hot weld to a good weld.