The washed pulps still contain a certain amount of lignin, which would cause a brownish colour of the paper. To obtain white paper, the pulp must be bleached. Whereas the lignin used to be removed from the pulp with elemental chlorine, today's paper industry uses other bleaching agents such as hydrogen peroxide, oxygen, chlorine dioxide, ozone and others. Chlorine dioxide bleached pulp is also referred to as ECF (elementary chlorine free) pulp. Pulp bleached without chlorine is called TCF (totally chlorine free).