We recently visited empty-nester friends, hence the delay in this month's comment. Our friends have successfully fledged both their offspring and have also managed to engineer their domestic arrangements and finances to allow them to take early retirement. They are now hoping to create a new life for themselves in a beautiful part of the world, namely Teesdale in England's North Pennines. One's ever so slightly younger, but nevertheless still middle-aged, mind cannot help but feel envious and simultaneously inspired to begin imagining its own work afterlife.

Such thoughts of life moving onwards and hopefully upward are brought into stark relief though when rambling among wild juniper bushes spotting rare orchids and mountain pansies with a view to staring and snapping photographically something somewhat older and entirely disinterested in the machinations of the middle-aged man - the enormous and potent waterfall on the Tees river known as High Force.

High Force has the largest volume of water falling over an unbroken drop when in full spate, hence its Nordic name of 'High Fosse'. Now, our friendly guides pointed out the horizontal layers of sedimentary rock (Carboniferous limestone) that emerge from the river below to form a sheer cliff capped with hard igneous dolerite (whinstone). Sandwiched between these two layers is a thinner filling Carboniferous sandstone, which was baked hard when the Whin Sill in which the waterfall finds itself was still molten and volcanic some 295 million years ago. This curtain type waterfall is about 29 meters from water level to its top over which the River Tees endlessly cascades. The timelessness of these rocks on the scale of our lifetimes, even the lifetime of humanity as a whole, the countless gallons of water that have poured over the sill heading for the sea between the industrial northern towns of Hartlepool and Redcar near Middlesbrough, do fill one with wonder alongside the scent of a juniper berry rubbed between finger tips to release its delightful scent.

The rusty tang to the water and the spray pouring over High Force is due to the presence of iron salts, of course, and iron oxide in particular. Iron oxide seems as timeless as the river the fall itself and has been both the boon and the bane of humanity for millennia. Intriguingly, our empty nester friends who were our tour guides and chauffeurs for the day are both erstwhile employees of the chemical industry that finds itself drinking deeply from the rivers that pour into the chilly North Sea some 80 miles to the East. And, one of the pair knows all too well the manufacturing of coatings and the various ingredients of paints.

Intriguingly, in their new part of the world, Teesdale, lots of folks paint their houses bright and white, a traditional, simple color, in modern paints often based on titanium dioxide and zinc oxide. Further South in the fascinating Yorkshire town of Knaresborough we had noticed buildings painted black and white in a checkerboard pattern. But, in my wife's part of the world Suffolk borders and into Suffolk, lots of houses are painted pink (as was the home in which I ostensibly grew up). Back in the day, whitewash mixed with pig's blood would've given the exterior a pastel yet bloody hue, the iron from the blood being the key (pardon the pun). Today, iron oxide can be used to give assist in giving paints a wide range of hues based on concentration from carnation pink to the terracotta.

It's always intrigued me that we, as a species, are so led by color and pattern (as apparently are other primates, birds, chameleons, cuttlefish and octopuses and presumably a range of other creatures. Pigments and iridescence repeatedly grab our attention whether it is the play of light on an orchid as a glimmer of sunshine breaks through northern clouds, the glistening rainbow across a waterfall in another sunny gap between the drizzle or the fluorescent glow of the quinine in that juniper-flavored gin and tonic with ice and a slice one might share with empty nesters in celebratory mood. Circle of life, folks, circle of life.

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".