Back in the day, when I did graphic arts with ink and film and stuff, I used to employ a darkroom technique called stretch and shrink, or something like that. What you did was use layers of vellum between litho film to "thicken" the image area or, conversely (using a negative on top), "thin" it out. One application, for example, was making outline type from a solid face. Now I am sure there must be a way to do this with Photoshop, but I can't figure it out. I even have Deke McClelland's books in front of me and I can't see anywhere where this is mentioned. But the method is similar to what must be going on when you make drop shadows (for example). Anyone have any pointers?

You might want to try this: Go to the channels tab and alt-click (or control-click, I am not sure on a pc) on the rgb or greyscale channel, to make a selection of the black and white in your image. In the case of a line drawing you will select the lines, but you will also respect the anti-aliasing, by 'half selecting' areas that are not completely black, nor completely white. When you invertyour selection you have effectively a selection of the black lines or and areas. You can thicken it. When you use the original selection you can thin it out. In the menu you will find 'select' and further below the option to, well, grow or shrink that selection. When you are drawing on a transparent layer, you can do the control-click-thingy on that layer, without searching for that channel tab. Good luck!

Can I have more details on the thickening and thinning? I think that's what I'm looking for.

Once you have the grown or shrinked selection you can fill it with black or use it to cut from the black. (I will be going skiing in Chech Republic for a week, so I hope this helps enough)

spreads and chokes terminology in photoshop is expand & contract with the selections as Hoofd mentioned. You would make a selection & save the selection as a channel, name it whatever you want. Then "expand" the selection & save it to a new channel, named whatever 2. Then deselect your work & reload the first channel & then apply the "contract" to it and save it also as a new channel named whatever 3. Then you have all 3 channels to work with to make your spreads & chokes.

"Expand" and "contract," that's the terminology I was looking for. Thanks.