Forming
From The Glossary of Digital Photography
A process that is performed on the capacitors of electronic flashes to ensure that they will hold a complete charge. Forming involves gradually charging and discharging the flash to build up insulating deposits in the capacitors and to build the dielectric between the plates. To reform a capacitor, it needs to be fully charged for about fifteen minutes and then discharged by firing the flash about five or six times. If the unit has not been used for several years, the forming process may be more technical because it needs to be done over a longer period of time and more slowly. This involves short applications of current. Guidance in this case should come from the manufacturer.
