Cut the rose so that only 2 inches of stem are still attached. Pour vinegar into a small cup. Place the cup in the sink and submerge the rose for about 30 seconds. Pull it out and gently shake off the excess vinegar. Dab the remaining drops with a paper towel. Tie the stem of the rose to the sink faucet so that it can hang freely. Allow it dry over the sink for at least one hour.
Pull off damaged or wilted petals before preparing the rose for pressing. To press the rose on its side, cut it again just below the calyx, which is the green bud just below the petals. For a top press, cut above the calyx at the very base of the petals. Cut out two sheets of cardboard the same size as a sheet of 8x11 paper. Lay three paper towels on top of one piece of cardboard.
Fold a junior-basket-size coffee filter in half. Cut out a circle about the size of a quarter in the filter for the top press method. Position the base of the flower in the center of the cardboard on top of the paper towels. Gently push down the outer petals, slipping the coffee filter over the whole flower. Let the inner petals poke out of the hole in the bottom, and slowly flatten the outer petals. Pin the outer edges of the coffee filter to the cardboard with thumbtacks. Flatten the inner petals gently. Place another uncut junior-basket-size coffee filter over those, pinning the edges with thumbtacks. For a side press, wrap the rose with a coffee filter so the petals won't stick to the paper towels during pressing.
Place three more paper towels over the rose. Top it off with another sheet of cardboard. Push down on the cardboard. Wrap the whole package with rubber bands to keep everything intact. Put the press in a refrigerator. Place a heavy book or two standard-sized 8-inch bricks on top of the cardboard to maintain more constant pressure. Wait two to three weeks for an optimal pressing. Once you are satisfied with the final result, coat the entire rose with a clear coat acrylic sealant spray, to keep it fully preserved and prevent crumbling.