Couplets typically articulate the aspirations of their owners. Wong says he remembers being attracted to them as a child, when his father used to hang them in their home.

One of his father's favourites was: In the twilight of his life, the great man is yet hale of heart/ The ageing steed lies in his stable, but still longs to gallop a thousand miles.

Those familiar with Chinese literature will know the reference to Cao Xueqin's novel, Dream of the Red Chamber, in which Jia Baoyu is ordered to compose couplets to highlight the grandeur of the new garden inside the family's residence. Without couplets, the place would be considered lacking in taste.

The pleasure of viewing the Lechangzai Xuan Collection is accentuated by their display at the Art Museum. Arranged on different levels to add rhythm to the flow created by the brushstrokes, every line of ink can be appreciated leisurely, in natural light, as you climb the stairs.

'It is a special form of calligraphy,' says Wong. 'The size of the words is much bigger and the spacing is particular. Even those who don't know the meaning of the couplets can share the sense of beauty because they're pictorial. There are different forms of Chinese writings, including archaic ones such as seal [xuan] scripts and clerical [di] scripts. During the Qing Dynasty there was a resurgence of interest in these ancient scripts.'

The former owner of a gallery that specialised in works by new Chinese artists, Wong is now a full-time landscape artist. 'I did very few couplets,' he says. 'Calligraphy requires a lot of discipline. In a way, it's harder than painting. One has to work within strict constraints.'

The Chinese University showed 150 couplets from Wong's collection in 2003 after they'd been shown at the University of Maryland in the US. Of those works, Wong says his favourite is by Yi Bingshou (1754-1815): Glimmer the moon over water of Lake Dongting/ Fragrant the orchid mists across Rivers Xiao and Xiang.

It is an adaptation of a work by Tang dynasty (618-907) poet Li Bai (701-762). Yi was best known for his clerical script and in this couplet - created in 1814, when his style was mature - the solid round strokes against the square create a strange tension.

'The words are usually big, as if they want to go beyond the limit of the scroll,' Wong says. 'It was executed on special paper. As bits of the adhesive material on the paper flaked off, along with the ink, it created a stunning visual effect, like words on weathered stone.'

The paper used for the couplets includes xuan paper, which gives an effect like cracked ice or stone. Others have hand-painted or hand-printed backgrounds with bits of gold, wax or precious pigments.

'Many calligraphers were officials given access to imperial materials,' Wong says. 'Driven by the demand, the master paper-makers did experiments. The ink they used was of exceptionally high quality, with a variety of tones.'

Another highlight is Pu Hua's couplet in running (xing-cao) script: Flipping through antique books and studying masterpiece paintings - there goes a long day/ Admiring ingenious writings and copying model-books - float I among idle clouds.

It was executed with spontaneity - the brush was wet at some points and dry at others, resulting in an elegant, yet casual touch. The running script, unlike the clerical one, allows a freer movement of the brush and requires skilful manipulation of the centre tip. There's a sense of freedom - along with an awkwardness and austerity is a lucidity that comes at a mature stage of a calligrapher's creative life.

Harold Mok of the Chinese University says such couplets are difficult to find - 'unless some collectors put them on the market, but that isn't common'. Mok says Chinese calligraphy is often underestimated. 'In the west, they don't have this form of art. It's only in recent years that people have started to look at calligraphy.'

Double Beauty II - Qing Dynasty Couplets from the Lechangzai Xuan Collection, Art Museum, Institute of Chinese Studies, Chinese University of Hong Kong. Ends May 13