The drums in the copiers originally developed by Xerox Corporation were manufactured with a surface coating of amorphous selenium (more recently ceramic or organic photoconductor or OPC), applied by vacuum deposition. Amorphous selenium will hold an electrostatic charge in darkness and will conduct away such a charge under light. In the 1970s, IBM Corporation sought to avoid Xerox's patents for selenium drums by developing organic photoconductors as an alternative to the selenium drum.