sentences:  Revisiting his notes in 1987 to draft a detailed reply to the abbreviated public version of Cahill's report, Walter McCrone chose the wrong sample to illustrate a "typical" black ink particle, selecting one which had been found only loosely attached to the ink.By focusing on this contamination, rich in chromium and iron, he gave Cahill the opportunity to re-emphasise his case in an essay for an expanded version of the 1965 official book, a few years later.In 1991, McCrone visited Yale to take new microsamples from the map, partly to check his earlier results, and partly to apply new techniques.