Hi,

A 'contrast mask positive' is a contact print of the original neg. developed very lightly, 30sec., 1 min., 2 min. depending on how much masking you need. It's usually used with Cibachrome printing but works well with any printing.

Any B&W film can be used and any shutter you can fit to your enlarger. Light meter a gray card and bracket both exposure and developement. Larger formats are easier to do, for 35mm I use a Weiss 'Super Duper' rack, it peg-registers the socket holes making it easy to register the film. Then just print the 'sandwhich' like a regular neg.

Back to back will make it an un-sharp mask which is easier to use. Emulsion to back will also work for printing. Emulsion to emulsion works to make positive slides but it's a bear for printing.

Hope it's a help.