As well as being a design feature, glass bricks can filter light into windowless spaces. In interiors, as in fashion, trends come and go, and come again. Take the chunky glass brick. So very 'now' in art deco buildings of the 1930s and 40s, it enjoyed a revival in the 70s and is cropping up more and more in funky flats around town. New Hong Kong devotees include C.J. and Gloria Wysocki - who installed a 120cm by 120cm glass brick window in their Mid-Levels bathroom, where it 'makes the room explode with light' - and Matthew Marsh, who has installed walls of the stuff in his small Mid-Levels flat. C.J. Wysocki reasons that glass brick is a useful material in Hong Kong, where apartments are often jammed up against each other: warping in the glass means they allow light into your home, but obstruct the view of nosy neighbours, and turn an ordinary space into one with plenty of personality. Designer Barrie Ho of Barrie Ho Architecture Interiors (3/F-4/F, 31 Wyndham Street, Central, tel: 2117 7662; www.barrieho.com ) says interior space should have a relationship with the outdoor environment, and glass bricks 'keep up the dialogue with nature'. Plus, he says, it's an easy design technique to apply. You may need a building permit, depending on where you plan to locate your glass brick feature and whether it will affect your building's structure, so check first with a surveyor, engineer or call the Building Department Enquiry Hotline (tel: 2626 1616) and ask to speak to a technical officer. The most straightforward approach is to replace an existing window with glass bricks. Most building contractors should be able to tackle the task, which involves the erection of scaffolding outside the window, removal of the old window, possible enlargement of the space by knocking out existing clay bricks or masonry and installation of the glass blocks. You will need to decide whether you want them constructed flush with your internal wall, or set back, which will allow you to have a windowsill. The process should be no messier than replacing a window, although it will take longer. And you might need to include a small exhaust fan if installing a glass-brick window in a bathroom. Marsh found glass blocks useful in his 900-square-foot, 1960s ground-floor flat, which had little natural light. His building contractor, Lee Pak-yiu of Hing Wah Decoration Design (tel: 2897 3885), used sledgehammers to demolish sections of column-and-beam masonry, which was 'easy but moderately messy', Marsh recalled. He would recommend moving out while it's being done. He had glass-brick walls installed in the living and dining area, bedroom and bathroom at a cost of about $7,000 a wall, including materials and labour. Lighting effects can be installed behind the bricks to give the appearance of a wall or window that glows, or to change its colour completely. Apart from adding light, glass bricks also provide privacy so there is no need to put up curtains.