Evidence in criminal cases is usually presented by government-recognized forensic science laboratories on evidence and submitted by police forces. Such laboratories are usually staffed by scientists and various specialists such as handwriting experts who, although generally quite experienced and skilled in their respective fields, seldom have experience in manufacture and general engineering. Occasionally, investigating police officers may instruct independent experts in such fields but, more commonly, independent experts are called in by lawyers acting for the accused in order to challenge or expand upon the evidence given to the court by scientists. In addition, insurance companies may have an interest in the outcome of a case so they too may wish to have material evidence examined by an independent expert and, if necessary, to challenge the interpretation given to the court. The cases that follow are selected from the authors’ experience in this field and, not surprisingly, have a strong metallurgical bias.