Sensitometric comparison of unexpired and expired duplicating films used in dentistry

This investigation compared the sensitometric properties of unexpired and expired duplicating films. The characteristic curve derived for a duplicating film is the negative slope of a solarization curve; that is, it is different in direction to that of a regular x-ray film. An expired duplicating film is slower than an unexpired duplicating film. Unlike a negative working film, which gains fog past its expiration date, a positive working film (for example, a duplicating film) gains contrast past its expiration date. An expired duplicating film has a narrower latitude than that of an unexpired duplicating film for a useful density range. Clinically, a duplicating film can be used years after its expiration date even though there is a change in its speed and contrast.