Since most toning processes either intensify or reduce the original
image, in order to obtain uniform results, _commence toning with
positive film of the correct density_.
Three standards of positive film have been chosen: Thin, Medium and
Normal. (See chart.) The “Thin” and “Medium” standards are obtained
by giving a slight overexposure and a shorter time of development.
The exact degree of intensification which takes place in any
particular case will soon be learned after a few trials.