Summarize the following:
Deep scratches in leather furniture may be scuffed and dirty, so before you attempt to repair the area, make sure it's clean first. Take a clean cloth and dip it in rubbing alcohol, then lightly buff the scratched area. Rubbing alcohol dries quickly. Let the area sit for about 10 minutes, and it should be dry. This method works most effectively with finished leather. If you have a deep cut in aniline leather, it may be irreparable. Unlike with a minor scratch, if your leather furniture is deeply scratched, the leather may be uneven, scuffed, or torn around the fringe of the scratch. Take a pair of scissors, and clip away any loose threads so that the area around the cut is smooth. Alternately, take a piece of fine-grit sandpaper (around 1200 grit) and sand the area surrounding the cut until it's smooth. Called "filler" for short, this material has the consistency of putty and will fill the gaps or cracks in the scratched section of your furniture. Using your finger or a small spatula, cover the scratch with heavy filler, until the scratched surface is even with the rest of the furniture's surface. Once you have applied the heavy filler, let it dry for about 30 minutes. Once the filler has been applied, take another sheet of 1200 grit sandpaper and smooth the surface of the filler. Leather heavy filler should be available at your local hardware store, or at a leather-goods store. Additionally, the furniture manufacturer may sell bonder or filler, or even send you some for free. Now that the scratch has been sealed and covered with heavy filler, you'll need to color the material to match the rest of the furniture piece. Apply the colorant to a sponge, and dab it evenly across the area covered by the heavy filler. Apply as many coats as necessary to match the color of the furniture, but remember to let each coat dry before applying a new one. To purchase leather colorant, you'll likely need to visit a leather-goods store or a furniture store that specializes in leather. This will seal and protect the dyed heavy filler, and should prevent the same area from being scratched again. Pour a small amount of the finish onto a sponge or clean cloth, and then lightly rub onto the scratched area of your furniture. Apply up to 3 or 4 coats for a consistent finish. As for the leather colorant, you'll probably need to purchase the leather finish at leather-goods store or a furniture store that specializes in leather. You may be able to purchase the heavy filler, colorant, and finish all together in a leather-repair set.

Summary:
Clean the area with rubbing alcohol. Sand or clip loose fibers around the edges of the cut. Apply leather heavy filler to the scratched area. Apply the correct shade of leather colorant. Apply a leather finish to the colored area.