You can do it with mercury, or you can do the Becquerel process - the Becquerel process involves no developing chemical, but instead the plate is re-exposed to full-spectrum light through a sheet of rubylith. You have to change your sensitization process if you plan to do Becquerel development. There are a number of books out there that have an extensive description of the process - the Christopher James book and "Coming Into Focus" by John Barnier are both good references.