An Irishman's Diary

THE part of Monaghan I grew up in and the city of Paris have little in common, it’s true. But they do share at least one unusual characteristic. They both have a lot of hydrated calcium sulphate – better known as gypsum – underneath them.

Or at least Paris used to have a lot. They stopped mining the mineral there back in the 1870s, by which time the French capital had already earned permanent naming rights to one of its applications – “Plaster of Paris” – even though such material did not originate in that city and, in fact, goes back thousands of years, to ancient Egypt and elsewhere.

Less celebrated is the link between gypsum and my home town of Carrickmacross, although it spawned what was surely the first new mining industry of post-independence Ireland. Strictly speaking, the mines are located a couple of miles east of the town, at a place called Knocknacran, where deposits were confirmed in 1921 and where extraction began even as a certain ill-fated Treaty was being debated in the Dáil.

The processing plant was, and is, located on the other side one of the two county borders nearby, in Meath. My Uncle Jamesie lived just up the road, in Cavan, and he used to drive a lorry for the “Gyp”, as the company is known. This seemed a very glamorous job to us as children. But whenever we stayed with him and Auntie Mary during school holidays, we often had to wait long into the night for him to return from epic journeys to places like Waterford and Kerry, with the sweets he always brought home.

At the age of seven, I had an even more intimate acquaintance with gypsum, this time in its Parisian form. In school one day, I fell over and broke my leg. The actual accident and most of the subsequent visit to hospital are now lost to memory.

Yet I’ll never forget the strange experience of having my injured limb wrapped in what looked a roll of thick, wet toilet paper that then quickly hardened into a shell.

Nor will I forget one of the side-effects of the plaster’s excellent bone-setting powers: the maddening itch that often accompanied it, about which you could do nothing. My leg was a prisoner for six long weeks. And the other memory that will stay with me forever is the happy day when the plaster came off again: a Parisian liberation with a twist.

THE EVENTthat so identified the French capital with plaster was a royal decree of 1667, which had nothing to do with bone-setting. It so happens that another of gypsum's uses is as a wall covering and, as such, it is also a very effective flame-retardant. Thus, a year after the Great Fire of London in 1666, worried that Paris might suffer a similar fate, Louis XIV ordered that all the city's old wooden-frame buildings should be covered with the stuff.

Work on another of his great projects, the Louvre, also began in 1667. That was before the “Roi Soleil” got nervous about living among the notoriously riot-prone Parisians and, having fire-proofed it, abandoned the city for his new home at Versailles. Even so, it may be thanks to his edict that a few pre-revolutionary houses still survive in Paris, their walls sometimes bulging where the wood under the plaster warped.

But there’s a certain paradox in gypsum’s role as a fire retardant, in that the chemical processes involved when the plaster is setting can also generate heat: up to 60 degrees Celsius in large quantities. On which subject, readers may recall an horrific court case in England two years ago. Art teachers everywhere certainly will.

It involved a teenage schoolgirl who had been working on a sculpture project using a bucketful of liquid plaster of Paris. In fact, she was trying to make a cast of her hands, and so held them in it for several minutes. Unfortunately the mixture set around her, heating as it did so. The unfortunate girl suffered severe burns, losing most of her fingers. Her school was fined £16,500 and, in a case of health-and-safety-not-gone-mad, it was a light enough punishment.

If its indigenous plaster saved Paris from the flames down the centuries, it indirectly caused other problems. After many centuries of quarrying, mostly for its geological cousin, limestone, gypsum contributed to a situation whereby in the late 18th century, the city was badly undermined. The fire-proofing of buildings did not help when, as in 1774, part of a street collapsed down a 30-metre-deep “bell-hole” (so-called because it’s narrow at the top, widening below).

Such collapses led to an urgent survey of the underground and work to buttress it where necessary. It was soon afterwards that the former mines were also exploited for another resource scarce in the city: space. The problem was especially acute in the old cemeteries. Thus, in an an early example of recycling, one calcium-rich material replaced another, and the former limestone quarries became the catacombs.