"Fresco" is a very good way of painting pictures on walls. It is much easier than painting on dry plaster because paint sinks into dry plaster immediately. Painting on fresh plaster means that the artist can spread the paint much easier. Also, fresco is permanent because the paint joins with the plaster so that the colours will not rub off. Frescoes last for hundreds of years. If they are kept clean and dry, the colours will stay bright for a very long time. Fresco does not use dangerous chemicals. The water, the calcite and the colours do not cause pollution. 