Tomorrow is March 17th, and as they have done every St Patrick’s Day weekend for 52 years, members of Chicago’s Journeymen Plumbers Union have already set about the herculean task of dying their city’s eponymous river a brilliant shade of emerald.
The transformation pays tribute to all that Irish immigration has done for the city, an act of recognition unique to Chicago, and one that is sure to make expat Paddies the world over turn green with envy.
But the extraordinary effect is surprisingly easy to achieve. All it takes, say the journeyman plumbers, is 18 kg of vegetable dye to give nearly 3 million cubic metres of water the hue of a leaky fluorescent marker.
As anyone who has ever attempted to buy wallpaper with a loved one will know, colours are notoriously difficult to define. One man’s Burgundy is close enough to another woman’s Maroon for Red to be a dangerously ambiguous catch-all term.
But what if more were at stake when choosing colours than marital happiness. What if the choice of one particular shade of blue over another constituted a religious sin. And – as if that weren’t bad enough – what if nobody had actually set eyes on the colour in question since the days of Ancient Rome.
This chromatic grey area is not a hypothetical situation. The disappearance of the colour t’khelet (pronounced with a properly phlegm-filled ‘kh’, if you please) was a pressing question in Jewish theology for well over a millennium. It took generations of rabbis, dye-makers and chemists to bring the dye back from the dead, and in the process explain just how it was that the Jews first got the blues.
In the Old Testament’s Book of Numbers (chapter 15, verse 38), the Lord tells Moses to instruct the Children of Israel to “make for themselves fringes on the corners of their garments, throughout their generations, and affix a thread of t’khelet on the fringe of each corner.”