Real or Fake, by Joe Nickell

Real or Fake provides a great introduction to authenticating signatures, documents, and artifacts. I've always liked Joe Nickell's approach to the paranormal -- he's a senior research fellow for the Committee for Skeptical Inquiry. Though he comes from a skeptical perspective, he always takes a fresh and honest look, and follows the evidence where it leads. The same careful method is obviously also useful in the cases he discusses in this book, which are more in the vein of Antiques Roadshow than Ghost Hunters. Another interesting detail is how useful collaboration is, since you can only be an expert in so many things. He consults paper experts, handwriting experts, printing experts, photography experts, microscopy experts, wood experts, coin experts, paint experts...
One expert may not be enough to make a conclusion, but when you have multiple lines of investigation pointing the same way, it makes it easier. The printing on the 'Stradiuarius' label was made with a 19th century font. The 'ebony' in its construction is some other wood stained black. Madam, your fiddle's a fake.