What fault will produce a dark film during processing?

A dark film during processing is a result of over-development. This occurs when the film is left in the developer solution for too long, or if the developer is excessively concentrated. Over-development can cause the image to become excessively dense, leading to overly dark areas that obscure finer details.

In this context, over-development increases the amount of silver halide crystals that are reduced to metallic silver, creating a film that is darker than intended. It is crucial for dental nurses and radiographers to adhere to precise processing times and solutions to avoid such errors.

The other options, while they can lead to different issues, do not specifically cause a dark film. A too weak developer would typically result in a underexposed or light image, while a developer that is too cold can also lead to insufficient development, causing lighter films due to inadequate chemical reaction. Incorrect processing sequences could contribute to various film quality issues but would not singularly lead to a dark film as over-development does.