A Christmas tree is one of the most popular traditions associated with the celebration of Christmas. It is normally an evergreen coniferous tree that is brought into a home or used in the open, and is decorated with Christmas lights and colourful ornaments during the days around Christmas. Tinsel and several types of garland, paper mache or ribbon are commonly used to decorate a Christmas tree. Delicate mould-blown and painted coloured glass Christmas ornaments were a specialty of Czech glass factories from the late 19th century, and have since become a large industry, complete with famous-name designers. Lighting with candles or electric lights (fairy lights) is commonly done, and a tree topper completes the ensemble. Strands of tinsel may be hung in groups from longer branches to simulate icicles, though this trend has gradually fallen off since the late 1970s. Baubles are another extremely common decoration, and usually consist of a fairly small hollow glass or plastic sphere coated with a thin metallic layer to make them reflective, and then with a further coating of a thin pigmented polymer in order to provide colouration.