Historically, ink was black, since the original ingredients were soot and iron-gall; iron-gall is still found today in blue-black ink. The colour blue only took hold in the 20th century and is today regarded as the typical fountain-pen ink — many career guides also recommend blue for signatures. Black has the advantage that it used to copy better, although that argument is moot with modern colour copiers. The most important point is to choose a water-soluble ink, since only such inks can be flushed out of the pen with simple means; royal blue inks are usually water-soluble. Pelikan 4001 royal blue and Lamy royal blue are inexpensive and good; Pelikan 4001 black, by contrast, tends to clog the feed and is not water-soluble.