The alloy is either 89% copper + 11% zinc or 93% copper + 7% zinc, which makes it a type of brass -- one that looks remarkably similar to gold. (Apparently ratios between those are less golden.) The name is from Christopher Pinchbeck (c.1670–1732), the London clock-maker who developed it and used it especially in watches. His surname come from a small village in Lincolnshire, which going back to Old English roots meant something like either “minnow stream” or “finch ridge” (which is a rather wide spread of meanings). Pinchbeck was used for a long time as for cheaper jewelry, and sometimes was passed off as the real gold, from whence the metaphoric extensions -- which didn't appear until 50 years after his death.
Where, in these pinchbeck days, can we hope to find the old agricultural virtue in all its purity?