If you collect salt cellars (a.k.a. salts, open salts, salt dips), you will want this book for a reference guide. Salt cellars were in vogue long before salt shakers existed. Your grandparents may not have used them, but your great-grandparents probably did--if they were born in the 1800s or early 1900s.
These small treasures are abundant. I find them in thrift shops, flea markets, and antique stores. Without "5000 Open Salts" (the title says it all), I would not be able to identify the pattern or age of the salt cellar. The book boasts hundreds of photographs of salts as well as reproductions of old catalogs pages that once advertised salts. Most of the salts are clear glass; some are tinted glass and others are ceramic, silver, silver-plated, or pewter.
The book also comes with a price guide, plus you can discover the availability or scarcity of each salt. Companies that made the salts are listed too. I've seen more than one book on salts, but this one is the best, in my opinion.
If you want to collect antiques, salt cellars are a good place to start. They are small (both the individual salts and the master salts) so they take up very little room. Most of them are inexpensive as well.