painting is not authentic

Technique of examinationOften a thorough examination (sometimes referred to as Morellian Analysis.[5]) of the piece is enough to determine authenticity. For example, a sculpture may have been created obviously with modern methods and tools. Some forgers have used artistic methods inconsistent with those of the original artists, such as incorrect characteristic brushwork, perspective, preferred themes or techniques, or have used colors that were not available during the artist’s lifetime to create the painting. Some forgers have dipped pieces in chemicals to "age" them and some have even tried to imitate worm marks by drilling holes into objects (See image, right).
While attempting to authenticate artwork, experts will also determine the piece’s provenance. If the item has no paper trail, it is more likely to be a forgery. Other techniques forgers use which might indicate that a painting is not authentic include:
Frames, either new or old, that have been altered in order to make forged paintings look more genuine. To hide inconsistencies or manipulations, forgers will sometimes glue paper, either new or old, to a painting's back, or cut a forged painting from its original size. Recently added labels or artist listings, onto unsigned works of art, unless these labels are as old as the art itself, suspicion should be aroused. While art restorers legitimately use new stretcher bars when the old bars have worn, new stretcher bars on old canvases might be an indication that a forger is attempting to alter the painting’s identity. Old nail holes or mounting marks on the back of a piece, might indicate that a painting has been removed from its frame, doctored and then replaced into either its original frame or different frame. Signatures, on paintings or graphics, that look inconsistent with the art itself (either fresher, bolder, etc.). Unsigned work that a dealer has “heard” is by a particular artist