WHAT astounded me was not so much my being mistaken for a clergyman. Nor that the challenge occurred, just where it did.

For mine is a face so chameleon that it has, in its time, compelled strangers to accost me with an outpouring of embarrassing symptoms in the belief that I was their family doctor; and one which, when it was still callow, was regularly and unjustly accused of belonging to the feckless someone who, for instance, had just misdelivered the milk.

As for the place: well, nothing vowed by a man of the cloth prohibits him from visting Paris or even from dining by candlelight at a restaurant in Montmartre, convenient as that district is for anyone intending a bout of late-night praying at the Sacre Coeur.

No, what was so mightily surprising as we squeezed past his table before re-emerging into the drizzle outside Le Lapin Agile was the very acuteness of the man. Of course, he got the vocation wrong and of course any Englishman abroad can spot another a mile off ... but how on earth was he able to put his question to probably the only chap within miles who had even heard of a particular small village in Northumberland?

Was I, he asked politely enough, but with an edge somehow implying he suspected my companion might be the churchwarden's wife, the Vicar of Percy Main?

A SPLENDID painting of Percy pit, at Percy Main Colliery, is on the front cover of an evocative little book, The Art of Mining: Thomas Hair's Watercolours of the Great Northern Coalfield, by Douglas Glendinning, the launch of which is being marked by an exhibition of Hair's work at the Hatton Gallery, Newcastle. Splendid pictorially, yes, but at what cost we shall see.

This mine became one of the most productive on Tyneside and in 1843, not long after Hair painted it, the 611 men and boys working there raised 104,000 tons of coal. As art historian Glendinning says, it was only a few years before Percy opened in 1807 that women and girls finished their last long and grueling shifts in the pits of Durham and Northumberland.

Hair used his watercolour sketches, which have been little shown and rarely published, as the basis for engravings he issued in book form. The accompanying text, together with other sources, has enabled Mr Glendinning to present some illuminating and often moving social detail alongside a selection of the paintings.

Female labour was used in some other coalfields for some years even after an 1839 Royal Commission was told: "When the nature of the horrible labour is taken into consideration, its extreme severity, its regular duration of between 12 and 14 hours daily ... and the tender age and sex of the workers, a picture is presented of deadly physical oppression and systematic slavery."

An 1842 law which prohibited the employment of boys younger than ten and any female underground was often flouted. Although it seems that the North-East had been among the first coalfields to stop sending women down the pit, it was not so squeamish about boys. A concerned visitor to Pemberton Main pit at Sunderland (later re-named Wearmouth colliery and now the site of the Stadium of Light football ground) reported in 1850 that he met a seven-year-old "trapper" - opener and closer of trap doors which controlled air-flow - and an even younger boy who earned 10d (4p) for a long day underground in what was the world's deepest pit when it opened.

"Yes, happy mother in your suburban villa and nursery, 10d a day was the price of that child's imprisonment," the observer wrote.

Not that Thomas Hair's paintings show such hardship or, indeed, much human activity at all. They are mainly of the collieries themselves, as industrial landscapes. Mr Glendinning explains that, almost without exception, British artists did not tackle social implications of the industrial revolution: it was the upper and middle classes who bought art and "images of young children and women, often malnourished and poorly clothed, shackled to long days of unremitting hard work would not have hung easily on the drawing room walls of the comfortably off".

How did colliery owners justify their use of this cheap labour, in a system where boys new to the pit were likely to have their legs tied together to prevent them straying and getting lost in the darkness? One manager's reply makes ugly reading:

"What we have to guard against is any obnoxious legislative interference in the established customs of our peculiar breed of Pitmen. The stock can only be kept up by breeding ... But if our meddling, morbid, humanity mongers get it infused into their heads that it is cruel unnatural slavery to work in the dark ... 12 hours a day in the pit, a screw in the system would be loose."

This, according to evidence given to the Children's Employment Commission in 1842, is what such "breeding" had done to the County Durham miner: "His stature is diminutive, his figure disproportionate and misshapen; his legs much bowed; his chest protruding ... his forehaead low and retreating; his habit is tainted with scrofula."

And, it added: "I never saw a jolly-looking pitman" - although a description elsewhere of Northumberland miners in 1841 makes a big thing of their flamboyant dress on the streets of holiday-time Newcastle, wearing patterned "posey jackets" and with flowers in their hat ribbons.

Hair himself speaks of the helpfulness and real politeness he met with "on the pit-heap".

Although Hair did not put the hardship in his pictures, his books did not ignore the cost in human lives of winning the coal that was making Britain wealthy and powerful. He listed a whole series of multiple-death accidents at the Jarrow mine, including those in 1826 and 1830 which each killed 42, and describes the "mute despair or frantic grief" of families outside the St Hilda colliery, South Shields, following an explosion in which 51 men and boys as young as nine died in 1839.

A man helping with the rescue was brought out of the mine, overcome by the choke gas: "He was questioned as to how he felt. 'I am not very well sir,' said he. 'I have two sons in there,' pointing to the place he had been driven from in his attempts to recover his children. One was 16, the other 22."

WELSH Nuts were the fuel of choice delivered by the South Suburban Co-op to my childhood home in wartime south London. They burned best. For the same effect in the North-East, at least during painter Hair's time, you asked for Wallsend coal and, almost unbelieveably, in 1850 you paid no more than 3d, or just over a new penny, a hundredweight for it, according to a contemporary price-list.

But the stuff quite probably did not come from the collieries in that Northumberland riverside town. For the name Wallsend had become the one accepted in the trade, nationally and even internationally, for top-quality coal which "kindles easily ... in burning it cakes or runs together, but not to such a hard solid mass as some other sorts, emitting at the same time, a great deal of heat as well as smoke and flame; it leaves a small quantity of residue or ashes".

It was to a pit across the Tyne from Wallsend, at Hebburn, that Humphrey Davy went to collect gases he used in experiments which helped him develop his famous safety lamp in 1815. It was, however, many years before the Davy Lamp was universally adopted and the few underground scenes depicted by Hair (after all, nothing could be painted in the darkness which predominated) had candle or flare lighting; it was a candle which caused the 1839 disaster at South Shields.

From about 1750 many pits were lit by the stream of sparks which resulted from a flint being held against a revolving steel wheel. A redeeming feature of this extraordinarily dangerous practice was that the colour of the sparks changed when fire damp was present, so giving a warning.

Hair's paintings of County Durham pits included Hetton, which was among North-East colleries that used George Stephenson's "patent travelling" steam engines to haul coal wagons several miles and sometimes with crude passenger carriages in tow. This was some years before the opening of the Stockton & Darlington Railway in 1825.

l Mr Glendinning's book (Tyne Bridge Publishing; 48 pages) is available from Newcastle libraries and bookshops at £6.99 or by post (£1 extra) from the publishers at City Library, Princess Square, Newcastle NE99 1DX.

The exhibition is at the Hatton Gallery until tomorrow. Admission is free (10am-5.30pm today and until 4.30 tomorrow).

l A chance find in my dictionary: a "Molly Maguire" - a member of a Pennsylvanian secret society formed to resist oppressive conditions in the mines, and crushed in 1877