The negative can be face up or down, just however you want it. A print frame keeps the negative evenly in contact with the paper during exposure. Hinged wood and glass print frames are available commercially, and are convenient to use. Commercial platemakers and blueprint machines have rollers or vacuum systems that keep the negative evenly in contact with the paper. Sunlight, ultraviolet lamp, arc light, commercial platemaker, sunlamp or other ultraviolet light sources may be used.
Exposure varies depending on lighting, negatives, coating techniques and other factors.
Try 10 minutes in bright sun or 75 units in violet arc light to start. The print will turn yellowish brown or brown when exposed. Any of these may give the final results you might want, so experiment and make test prints to find the correct exposure. Image will turn reddish brown or darker brown in water. Fix in fixer with agitation for about 5 minutes.