She wanted to be a farmer, but her father and mother - writer and painter respectively - discouraged that ambition, and sent her to art school instead. From the start she concentrated on engraving, and at the Central School of Arts and Crafts her principal teacher was Gertrude Hermes. Since then she has gone from strength to strength: now in her sixties, winner of many awards, she has held a dozen solo exhibitions and is widely admired as a teacher.
Together with her husband Chris (also an artist), she lives in a long, narrow house hard by the river, surrounded by walls designed to repel flood tides, and in particular the Severn bore. The building is allegedly founded on three sunken trows, or Severn barges, and she has been happy to accept this tradition without exploratory excavation.
She feels that English wood engravers, herself included, are still very much in thrall to Thomas Bewick, the celebrated print-maker and illustrator who flourished in Northumberland at the end of the 18th century, specialising in birds, animals and landscapes. "We have this ghost of Bewick sitting on our shoulders," she says. "I don't know any English engraver who's managed to get away from it completely."
Certainly her own work is strongly pastoral: she takes many of her subjects from nature, and excels at catching - in black and white - the varied textures of leaves and grass and stone walls, of animals' hides and birds' feathers. Indeed, she regards wood engraving as "part of the whole ethic of country living".
She has only to look out of the window beside her work bench to find inspiration. Recently an enormous flock of lapwings began working the tidal estuary, and, after much gloomy talk about lapwing disappearing, she was delighted to see them. "They're magic to watch," she says, "especially when the sun's shining. The black and white flash is almost like silver paper." The result: a beautiful small engraving of two peewits wheeling above a big S-bend of water.
There is a key difference between wood cutting, in which the artist works along the grain, and wood engraving, in which he or she cuts across it. The second is by far the finer, more detailed form, so that engravings tend to be smaller. The best blocks are made of boxwood, which is exceptionally hard, close-grained and heavy. Every block is composed of small cubes glued together to form a square or rectangle, of which one side is planed and sanded, leaving a surface almost as smooth as marble.
Such raw material is far from cheap: boxwood blocks cost from pounds 1 to pounds 1.80 per square inch, so that a medium-sized one, six inches by eight, can come out at the best part of pounds 100. Boxwood does not take kindly to being left in sunlight or on radiators - it buckles - but if properly treated will survive indefinitely, not least because it is poisonous and so impervious to woodworm.
Many engravers, Americans especially, now work on plastic - but that, to Sarah, is an unrewarding medium. "I hate plastic," she says. "It's far too slithery. There's something absolutely wonderful about engraving on wood: the marvellous crunching." Ranged on her work bench is a set of specialised tools like tiny chisels - a scorper, a spitsticker, a tint- tool and a graver or burin. To a layman they all look much the same, with devilishly sharp points, but each has its particular role.
The start of any engraving is a series of drawings. "Because you're working to a set size, you need to re-draw and re-draw and re-draw to get the composition right," she says. "The risk is that this may deaden the picture, so you have to make a conscious effort to keep the drawing lively."
She traces the finished sketch on to the block through transfer paper - and away she goes, obviously cutting with care, but sometimes also at speed. "It's often much better if you do fly at it," she says. "That way you get a bit of spontaneity going." The finished block - the result of at least a week's solid work - goes under a mighty, cast-iron press dating from 1840 - and as many prints can be run off as are needed for an edition.
Every cut an engraver makes lets light into the picture. As one beginner said, "You feel like God: let there be light, and there is light!" The penalty is that you cannot afford to make mistakes. Once an area of the surface has been excised, it cannot be replaced.
Boxwood is too expensive for students to learn on. "You must give them something reasonably cheap," says Sarah. "Otherwise they feel they're cutting into a piece of gold." The best alternative is lemon wood - a collective term for several varieties. On a recent course at Dartington Hall in Devon she was amazed by the lack of inhibition with which her 14 learners pitched in, each finishing two or three engravings in the weekend.
She was also surprised by a snippet of news that one of her own pieces elicited. When she showed a print of chickens foraging under maize, somebody came up with the slightly sinister information that pheasants, which normally love maize, will not go near crops grown from genetically modified seed.
Until recently Sarah was Chairman of the Society of Wood Engravers, which has 70 members and organises an annual touring exhibition. This year, after a "tremendously successful" start at the Victoria Gallery in Bath, the show is now in Canterbury. One of its attractions, she finds, is that it is enlivened by engravings from non-members in Eastern Europe and Russia, where artists have broken away from the Bewick tradition into adventurous new fields.
Yet some of her own work is anything but representational. One enjoyable commission was to illustrate books of the Old Testament for a Reader's Digest edition of the Bible. She left her depiction of Jonah to the last because she felt it would be the most fun - and sure enough, it is a triumph, with the old boy looking incredibly crafty as he scoots along in the belly of the speeding whale.
The Society of Wood Engravers' exhibition is at the Royal Museum and Art Gallery, High Street, Canterbury, until 13 MarchReuse content