A long, raised worktable and a raised walkway the length of the room will make it a whole lot easier to apply long strips of wallpaper to the ceiling. To create the worktable, place a large piece of plywood or scrap wood on top of two stepladders. Make the walkway with plywood or scrap wood set on milk crates.
Good prep work is the key to beautiful results. Remove any old wall coverings, then sand and clean the surface. Use a commercial cleaning solution or make your own with a mixture of 2 cups bleach to 1 gallon water. The clay-based adhesive used to apply this wall covering won't bond properly unless the application surface is very clean.
To test the surface for loose paint, use a razor blade to cut an X about 1" long into the ceiling paint, put a piece of adhesive tape against the X , and snap it off quickly. If any paint chips come off onto the tape, you need to sand the surface again.
Prime the clean surface with acrylic primer designed for use with clay-based adhesive. Let it dry for 24 hours.
A straight line on the ceiling is necessary for the application of the first run of wallpaper. Wallpaper rolls come in widths of 20 1/2", so a line measured 20" from the edge of the ceiling allows overlap for trimming. Measure 20" from the molding at each end of the ceiling. Pound a nail at one 20" mark (Image 1), attach a chalk line, and run the chalk line the length of the ceiling (Image 2).
Bring the wallpaper sheet out an extra inch against the ceiling molding on the right side, and set in place along the chalk line (Image 1). Hold up only about a foot of wall covering at a time; carefully press in into place (Image 2).
After you've attached about a foot or so of wallpaper, go over it with a wallpaper-smoothing brush. Apply a fair amount of pressure to ensure adhesive bonding. Work down the length of the sheet, keeping the edge of the wallpaper plumb with the chalk line.
Cut the next length of wallpaper from the roll, adding an extra 3" to 6" on each end to allow for pattern matching. Apply the next strip of wallpaper to the ceiling, taking care to match the pattern and to butt the edges of the adjacent length of wallpaper tightly, with no overlapping.
Use a trim guard to make sure the wallpaper fits snugly against the edge of the molding (Image 1). Run a razor knife along the trim guard to cut off the excess wallpaper (Image 2); make overlapping cuts to make sure you cut all the way through. Pull off the strip of excess wallpaper and use a wet sponge to clean any adhesive off the molding at the wallpaper line.
After 24 hours, the wallpaper can be painted. The clay-based adhesive discolors the wallpaper, making painting a necessity. Apply paint with a high-nap roller to ensure good coverage. The historical look of a plaster, tin or leather-embossed ceiling is achieved with the paint finish chosen: flat latex gives a plaster effect, high-gloss latex in a dark color simulates leather, and automobile enamel gives a metallic look.