Your Artley would be from around 1984 or 1985. There should be a 2-digit prefix in front of the serial number. Add 50 to that number and that will be the year of manufacture. See:http://www.musictrader.com/artley.html
The 18-0 is a student model Artley flute. It would be plated with either nickel or silver. If it turns brown or black, that is silver tarnish and would be a silver plated model. Be careful using silver polish on the body and keys. I recommend that you leave polishing to your flute technician. If silver polish gets into the key rods, it can contaminate the oil and cause excessive wear to the mechanism.