Blanch, peel and core tomatoes before chopping. Prepare spice bag using pickling spice and mustard seed tied in a bag. In a large kettle, combine prepared tomatoes, celery, onions, peppers, vinegar, salt and spice bag. Bring contents to a slow boil stirring occasionally. Lower heat and simmer uncovered for 3-1/2 to 4 hours. Continue simmering until desired consistency is reached. When chili sauce has reached the desired thickness, add the brown sugar and cook an additional 30 minutes. Pack in sterile canning jars.