From your description this sounds like how the early platinotype printers used to control contrast. Developer temperature effects development time. By using a cool developer with glycerin on the print and in the developer they could really slow down the development time which allowed them to control local contrast with a brush. It's very effective, although for most purposes it's easier to use a dash of potassium dichromate coupled with some judicious dodging and burning.
Originally Posted by donbga