The invention of padlocks dates back to 500 B.C. during the Roman era. Padlocks quickly advanced in technology and function due to their necessity. The basic shape of a padlock consists of the case, the solid part of the lock where the key fits, and the shackle, the U-shaped piece of metal that disconnects from the case on one side. With so many types of antique padlocks, you can choose to collect just one type or have a varied collection that spans the ages.
Learn your stuff before you look for a padlock at antique stores, auctions and flea markets.
Look at the shape. There are many different types of padlocks, ranging from practical shapes to more decorative ones. Rectangular and circular locks are most common; they differ in the size, shape and girth of the shackle. Decorative-shaped locks are often easier to identify because they are rarer.
Identify the metal. Many locks from the past 200 years are steel, brass or a combination, but there are other metals out there, such as iron. Metals can be identified by their color: brass is yellow or reddish; iron is silvery gray; and steel is brownish gray. Bring a magnet with you when looking for padlocks. Copper, brass and aluminum are not magnetic.
Examine the key. Not every padlock collector collects the keys with their locks; the keys often have been lost over the years. If you are lucky enough to find a padlock with authentic, original keys, their shape can be invaluable to figuring out the make and year of the lock.
Look for inscriptions. Many padlocks made in the last hundred years have the company and their manufacture date inscribed on the case. Research the company and make sure the shape and metal of the padlock are authentic.
Research your lock in your book. Using the information you have gleaned by looking at you lock, find a match in "The National Locksmith Guide to Antique Padlocks." This should help you pinpoint the year and, possibly, the make of your padlock.
Just because a lock looks old doesn't mean it isn't a fake or reconstruction, lessening or depleting its value.