Volume 34, Issue 6 (November 1989)
Photographically Subtracting Interfering Images from ESDA Print
Documents containing indentations from other written papers may also contain original written material on the reverse side of the page. When such a document is processed on an Electrostatic Detection Apparatus (ESDA), both the subject indentations and the writing on the reverse of the paper are often recorded. It is usually very difficult to decipher the indented writing because of the overlapping images from the reverse of the paper. It is possible, however, to subtract these interfering images by making a positive transparency of the original writing on the reverse of the paper and sandwiching it with a negative of the ESDA. This method provides a clear and accurate record of the subject indentations alone.