Performance art 5 : criteria of choice of material

This artist tried to use glue to cover (or "erase) the symbol of the Hong Kong Police, so as to criticise the over-power of the power force. I have also asked them why they chose to use certain kind of material (say, here is the material of glue, and others include washing powderm water, soil, chalk and etc), they replied that their main concern about the materical used was whether the materical will be easily cleaned and the site can be easily be recovered. For example, when the material glue gets dry, it will become invisible and transparent, and thus the performance itself will not affect the physical appearance of the site after the show, and more importantly, the police then will not have evidence to charge those performance artists.

One more example of the amazing use of material is the use of water. One artist used water to write the Chinese word "拆"("demolish" in English) on the wall of Hong Kong City Hall, in where supposingly it is too grand and too exposing to write sometime on it. However, since he understood the powerful characteristic of water---visible and then invisible, any authority can never catch him regarding to any kind of law. How clever are the artists in the use of materials!!