The Warnerke Standard Sensitometer consisted of a frame holding an opaque screen with an array of typically 25 numbered, gradually pigmented squares brought into contact with the photographic plate during a timed test exposure under a phosphorescent tablet excited before by the light of a burning Magnesium ribbon. The speed of the emulsion was then expressed in 'degrees' Warnerke (sometimes seen as Warn. or °W.) corresponding with the last number visible on the exposed plate after development and fixation. Each number represented an increase of 1/3 in speed, typical plate speeds were between 10° and 25° Warnerke at the time. COUNT 5
QSN1 What consists of 25 pigmented squares touching a plate below a phosphorescent tablet under the light of a burning Magnesium ribbon? ANS1 The Warnerke Standard Sensitometer QSN2 What do degrees Warnerke measure? ANS2 The speed of the emulsion QSN3 How much speed is associated with each degree Warnerke? ANS3 an increase of 1/3 in speed QSN4 What were usual ranges of Warnerke speeds?  ANS4 between 10° and 25° Warnerke QSN5 What does the last exposed number on the plate represent?  ANS5 'degrees' Warnerke