Old Man with His Grandson, Ghirlandaio (c1490)

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Artist: Domenico Ghirlandaio (1449-94) ran one of the most successful painting studios in Renaissance Florence. His speciality was fresco painting, in churches such as Santa Maria Novella and the Ognissanti in Florence, as well as the Palazzo Vecchio. Once, commissioned to paint frescos in an abbey further afield, Domenico, his brother David and their collaborators found to their disgust that they were treated like servants, rather than a famous artist and his crew.

They were fed atrocious scraps "fit only for a hangman", according to Ghirlandaio's 16th-century biographer, Vasari. It was time to assert the status of the artist. David grabbed a hard loaf of bread and beat the steward until he was almost dead; when the abbot came to protest, he told him the talent of his brother Domenico "was worth more than all the pigs of abbots like him that ever lived in that monastery".

Thereupon the abbot treated them with due respect. Through such confrontations the painter was elevated from artisan to genius in 15th-century Florence, though painting was still practised artisan-style in workshops with apprentices. Florentines loved Ghirlandaio's frescos for their lifelike portraits of contemporary faces among the saints and Roman soldiers. It was said he could capture a portrait of a passerby instantly in his sketchbook. Vasari raved over the verisimilitude of his fresco figures, remembering, for example, a bishop wearing spectacles and chanting prayers for the dead; he was so lifelike that the only clue that he was painted was the lack of sound.

Subject: A 15th-century patrician and a boy - his grandson, according to tradition.

Distinguishing features: This immediately touching portrait, on a wooden panel made half a millennium ago, is emotive proof of Leon Battista Alberti's claim in his 1435 treatise De Pictura that painting possesses a truly divine power, making the absent present and representing the dead to the living many centuries later. Painting's capacity to catch a passing moment is acute in this portrait of an unknown wealthy man and a child. It seems valedictory, as we see the old man as if through the eyes of the little boy looking up at the noble ruin of a venerable face.

That face is dominated by the old man's nose, a massive tumult of bulbous growths - perhaps a product of the skin condition rosacea. The little boy, his own face a perfect, harmonious and childishly chubby example of ideal Renaissance beauty, complete with golden, curling locks, appears to be examining the disfigured face of age with clear-eyed curiosity. At the same time, the boy's hand is warm and loving, as is the downward, benevolent gaze of the old man out of heavily lidded, wrinkled, almost tortoise-like eyes.

Youth and age, beauty and the ravages of time contemplate each other; the boy is looking at his future, the proud old man at one who will preserve his memory, as this painting does. The man's fur-lined red robe and the boy's elegant dress and hair indicate that they bear a noble family name, though it is lost to us. Out of the window we see a landscape that combines ruggedness and delicacy, like the portrait's juxtapositions. The gentle, hilly countryside leads to a hard rocky peak, as forbidding as the old man's nose. Like a traveller approaching a natural wonder, the boy looks up in awe at the old man, beloved monster.

Inspirations and influences: Michelangelo was apprenticed to Ghirlandaio, but later denied it in order to emphasise his originality.

Where is it? Louvre, Paris.